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<rfc ipr="pre5378Trust200902" docName="draft-ietf-openpgp-crypto-refresh-13" cat <rfc xmlns:xi="http://www.w3.org/2001/XInclude"
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<front> number="9580"
<title>OpenPGP</title> category="std"
consensus="true"
submissionType="IETF"
obsoletes="4880, 5581, 6637"
updates=""
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<front>
<title abbrev="OpenPGP">OpenPGP</title>
<seriesInfo name="RFC" value="9580"/>
<author initials="P." surname="Wouters" fullname="Paul Wouters" role="editor "> <author initials="P." surname="Wouters" fullname="Paul Wouters" role="editor ">
<organization>Aiven</organization> <organization>Aiven</organization>
<address> <address>
<email>paul.wouters@aiven.io</email> <email>paul.wouters@aiven.io</email>
</address> </address>
</author> </author>
<author initials="D." surname="Huigens" fullname="Daniel Huigens"> <author initials="D." surname="Huigens" fullname="Daniel Huigens">
<organization>Proton AG</organization> <organization>Proton AG</organization>
<address> <address>
<email>d.huigens@protonmail.com</email> <email>d.huigens@protonmail.com</email>
</address> </address>
</author> </author>
<author initials="J." surname="Winter" fullname="Justus Winter"> <author initials="J." surname="Winter" fullname="Justus Winter">
<organization>Sequoia-PGP</organization> <organization>Sequoia PGP</organization>
<address> <address>
<email>justus@sequoia-pgp.org</email> <email>justus@sequoia-pgp.org</email>
</address> </address>
</author> </author>
<author initials="Y." surname="Niibe" fullname="Yutaka Niibe"> <author initials="Y." surname="Niibe" fullname="Yutaka Niibe">
<organization>FSIJ</organization> <organization>FSIJ</organization>
<address> <address>
<email>gniibe@fsij.org</email> <email>gniibe@fsij.org</email>
</address> </address>
</author> </author>
<date year="2024" month="January" day="04"/> <date year="2024" month="May"/>
<area>sec</area> <area>sec</area>
<workgroup>Network Working Group</workgroup> <workgroup>openpgp</workgroup>
<keyword>Internet-Draft</keyword>
<abstract> <abstract>
<t>This document specifies the message formats used in OpenPGP.
OpenPGP provides encryption with public key or symmetric cryptographic algorithm
s, digital signatures, compression, and key management.</t>
<t>This document is maintained in order to publish all necessary information nee
ded to develop interoperable applications based on the OpenPGP format. It is not
a step-by-step cookbook for writing an application. It describes only the forma
t and methods needed to read, check, generate, and write conforming packets cros
sing any network. It does not deal with storage and implementation questions. It
does, however, discuss implementation issues necessary to avoid security flaws.
</t>
<t>This document specifies the message formats used in OpenPGP. <t>This document obsoletes RFCs 4880 ("OpenPGP Message Format"), 5581 ("Th
OpenPGP provides encryption with public-key or symmetric cryptographic algorithm e Camellia Cipher in OpenPGP"), and 6637 ("Elliptic Curve Cryptography (ECC) in
s, digital signatures, compression and key management.</t> OpenPGP").</t>
<t>This document is maintained in order to publish all necessary information nee
ded to develop interoperable applications based on the OpenPGP format.
It is not a step-by-step cookbook for writing an application.
It describes only the format and methods needed to read, check, generate, and wr
ite conforming packets crossing any network.
It does not deal with storage and implementation questions.
It does, however, discuss implementation issues necessary to avoid security flaw
s.</t>
<t>This document obsoletes: RFC 4880 (OpenPGP), RFC 5581 (Camellia in OpenPGP) a
nd RFC 6637 (Elliptic Curves in OpenPGP).</t>
</abstract> </abstract>
<note title="About This Document" removeInRFC="true">
<t>
The latest revision of this draft can be found at <eref target="https://
openpgp-wg.gitlab.io/rfc4880bis/"/>.
Status information for this document may be found at <eref target="https
://datatracker.ietf.org/doc/draft-ietf-openpgp-crypto-refresh/"/>.
</t>
<t>
Discussion of this document takes place on the
OpenPGP Working Group mailing list (<eref target="mailto:openpgp@ietf.or
g"/>),
which is archived at <eref target="https://mailarchive.ietf.org/arch/bro
wse/openpgp/"/>.
Subscribe at <eref target="https://www.ietf.org/mailman/listinfo/openpgp
/"/>.
</t>
<t>Source for this draft and an issue tracker can be found at
<eref target="https://gitlab.com/openpgp-wg/rfc4880bis"/>.</t>
</note>
</front> </front>
<middle> <middle>
<section anchor="introduction">
<section anchor="introduction"><name>Introduction</name> <name>Introduction</name>
<t>This document provides information on the message-exchange packet forma
<t>This document provides information on the message-exchange packet formats use ts used by OpenPGP to provide encryption, decryption, signing, and key managemen
d by OpenPGP to provide encryption, decryption, signing, and key management func t functions.
tions. It is a revision of <xref target="RFC4880"/> ("OpenPGP Message Format"), w
It is a revision of RFC 4880, "OpenPGP Message Format", which is a revision of R hich is a revision of <xref target="RFC2440"/>, which itself replaces <xref targ
FC 2440, which itself replaces RFC 1991, "PGP Message Exchange Formats" <xref ta et="RFC1991"/> ("PGP Message Exchange Formats").</t>
rget="RFC1991"/> <xref target="RFC2440"/> <xref target="RFC4880"/>.</t> <t>This document obsoletes <xref target="RFC4880"/> (OpenPGP), <xref targe
t="RFC5581"/> (Camellia in OpenPGP), and <xref target="RFC6637"/> (Elliptic Curv
<t>This document obsoletes: <xref target="RFC4880"/> (OpenPGP), <xref target="RF es in OpenPGP). At the time of writing, this document incorporates all outstandi
C5581"/> (Camellia in OpenPGP) and <xref target="RFC6637"/> (Elliptic Curves in ng verified errata, which are listed in <xref target="errata-listing"/>.</t>
OpenPGP). <t>Software that has already implemented those previous specifications may
This document incorporates all - at the time of writing - outstanding verified e want to review <xref target="upgrade-guidance"/> for pointers to what has chang
rrata which are listed in <xref target="errata-listing"/>.</t> ed.</t>
<section anchor="terms">
<t>Software that has already implemented those previous standards may want to re <name>Terms</name>
view <xref target="upgrade-guidance"/> for pointers to what has changed.</t> <t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp
14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
<section anchor="terms"><name>Terms</name>
<t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUI
RED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECO MMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>", NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECO MMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to be i nterpreted as "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to be i nterpreted as
described in BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they described in BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they
appear in all capitals, as shown here.</t> appear in all capitals, as shown here.</t>
<t>The key words "Private Use", "Specification Required", and "RFC Requi
<t>The key words "PRIVATE USE", "SPECIFICATION <bcp14>REQUIRED</bcp14>", and "RF red" that appear in this document when used to describe namespace allocation are
C <bcp14>REQUIRED</bcp14>" that appear in this document when used to describe na to be interpreted as described in <xref target="RFC8126"/>.</t>
mespace allocation are to be interpreted as described in <xref target="RFC8126"/ <t>Some terminology used in this document has been improved from previou
>.</t> s versions of the OpenPGP specification.
<t>Some terminology used in this document has been improved from previous versio
ns of the OpenPGP specification.
See <xref target="terminology-changes"/> for more details.</t> See <xref target="terminology-changes"/> for more details.</t>
</section>
</section> </section>
</section> <section anchor="general-functions">
<section anchor="general-functions"><name>General functions</name> <name>General Functions</name>
<t>OpenPGP provides data confidentiality and integrity for messages and da
<t>OpenPGP provides data confidentiality and integrity for messages and data fil ta files by using public key and/or symmetric encryption and digital signatures.
es by using public-key and/or symmetric encryption, and digital signatures.
It provides formats for encoding and transferring encrypted and/or signed messag es. It provides formats for encoding and transferring encrypted and/or signed messag es.
In addition, OpenPGP provides functionality for encoding and transferring keys a In addition, OpenPGP provides functionality for encoding and transferring keys a
nd certificates, though key storage and management is beyond the scope of this d nd certificates, though key storage and management are beyond the scope of this
ocument.</t> document.</t>
<section anchor="confidentiality-via-encryption">
<section anchor="confidentiality-via-encryption"><name>Confidentiality via Encry <name>Confidentiality via Encryption</name>
ption</name> <t>OpenPGP combines symmetric key encryption and (optionally) public key
encryption to provide confidentiality.
<t>OpenPGP combines symmetric-key encryption and (optionally) public-key encrypt When using public keys, first the object is encrypted using a symmetric key encr
ion to provide confidentiality. yption algorithm.
When using public keys, first the object is encrypted using a symmetric encrypti
on algorithm.
Each symmetric key is used only once, for a single object. Each symmetric key is used only once, for a single object.
A new "session key" is generated as a random number for each object (sometimes r eferred to as a session). A new "session key" is generated as a random number for each object (sometimes r eferred to as a "session").
Since it is used only once, the session key is bound to the message and transmit ted with it. Since it is used only once, the session key is bound to the message and transmit ted with it.
To protect the key, it is encrypted with the receiver's public key. To protect the key, it is encrypted with the receiver's public key.
The sequence is as follows:</t> The sequence is as follows:</t>
<ol spacing="normal" type="1"><li>
<t><list style="numbers"> The sender creates a message.
<t>The sender creates a message.</t> </li>
<t>The sending OpenPGP implementation generates a random session key for this <li>The sending OpenPGP implementation generates a random session key
message.</t> for this message.
<t>The session key is encrypted using each recipient's public key. </li>
These "encrypted session keys" start the message.</t> <li>The session key is encrypted using each recipient's public key.
<t>The sending OpenPGP implementation optionally compresses the message, and t These "encrypted session keys" start the message.
hen encrypts it using a message key derived from the session key. </li>
The encrypted message forms the remainder of the OpenPGP message.</t> <li>The sending OpenPGP implementation optionally compresses the messa
<t>The receiving OpenPGP implementation decrypts the session key using the rec ge and then encrypts it using a message key derived from the session key.
ipient's private key.</t> The encrypted message forms the remainder of the OpenPGP Message.
<t>The receiving OpenPGP implementation decrypts the message using the message </li>
key derived from the session key. <li>The receiving OpenPGP implementation decrypts the session key usin
If the message was compressed, it will be decompressed.</t> g the recipient's private key.
</list></t> </li>
<li>The receiving OpenPGP implementation decrypts the message using th
<t>When using symmetric-key encryption, a similar process as described above is e message key derived from the session key.
used, but the session key is encrypted with a symmetric algorithm derived from a If the message was compressed, it will be decompressed.
shared secret.</t> </li>
</ol>
<t>Both digital signature and confidentiality services may be applied to the sam <t>When using symmetric key encryption, a similar process as described a
e message. bove is used, but the session key is encrypted with a symmetric algorithm derive
d from a shared secret.</t>
<t>Both digital signature and confidentiality services may be applied to
the same message.
First, a signature is generated for the message and attached to the message. First, a signature is generated for the message and attached to the message.
Then the message plus signature is encrypted using a symmetric message key deriv Then, the message plus signature is encrypted using a symmetric message key deri
ed from the session key. ved from the session key.
Finally, the session key is encrypted using public-key encryption and prefixed t Finally, the session key is encrypted using public key encryption and prefixed t
o the encrypted block.</t> o the encrypted block.</t>
</section>
</section> <section anchor="authentication-via-digital-signature">
<section anchor="authentication-via-digital-signature"><name>Authentication via <name>Authentication via Digital Signature</name>
Digital Signature</name> <t>The digital signature uses a cryptographic hash function and a public
key algorithm capable of signing.
<t>The digital signature uses a cryptographic hash function and a public-key sig
nature algorithm.
The sequence is as follows:</t> The sequence is as follows:</t>
<ol spacing="normal" type="1"><li>
<t><list style="numbers"> The sender creates a message.
<t>The sender creates a message.</t> </li>
<t>The sending implementation generates a hash digest of the message.</t> <li>The sending implementation generates a hash digest of the message.
<t>The sending implementation generates a signature from the hash digest using </li>
the sender's private key.</t> <li>The sending implementation generates a signature from the hash dig
<t>The signature is attached to or transmitted alongside the message.</t> est using the sender's private key.
<t>The receiving implementation obtains a copy of the message and the message </li>
signature.</t> <li>The signature is attached to or transmitted alongside the message.
<t>The receiving implementation generates a new hash digest for the received m </li>
essage and verifies it using the message's signature. <li>The receiving implementation obtains a copy of the message and the
If the verification is successful, the message is accepted as authentic.</t> message signature.
</list></t> </li>
<li>The receiving implementation generates a new hash digest for the r
</section> eceived message and verifies it using the message's signature.
<section anchor="compression"><name>Compression</name> If the verification is successful, the message is accepted as authentic.
</li>
<t>An OpenPGP implementation <bcp14>MAY</bcp14> support the compression of data. </ol>
Many existing OpenPGP messages are compressed. </section>
<section anchor="compression">
<name>Compression</name>
<t>An OpenPGP implementation <bcp14>MAY</bcp14> support the compression
of data.
Many existing OpenPGP Messages are compressed.
Implementers, such as those working on constrained implementations that do not w ant to support compression, might want to consider at least implementing decompr ession.</t> Implementers, such as those working on constrained implementations that do not w ant to support compression, might want to consider at least implementing decompr ession.</t>
</section>
</section> <section anchor="conversion-to-base64">
<section anchor="conversion-to-base64"><name>Conversion to Base64</name> <name>Conversion to Base64</name>
<t>OpenPGP's underlying representation for encrypted messages, signature
<t>OpenPGP's underlying native representation for encrypted messages, signatures s, keys, and certificates is a stream of arbitrary octets.
, keys, and certificates is a stream of arbitrary octets. Some systems only permit the use of blocks consisting of 7-bit, printable text.
Some systems only permit the use of blocks consisting of seven-bit, printable te For transporting OpenPGP's raw binary octets through channels that are not safe
xt. to transport raw binary data, a printable encoding of these binary octets is def
For transporting OpenPGP's native raw binary octets through channels that are no ined. The raw 8-bit binary octet stream can be converted to a stream of printabl
t safe to transport raw binary data, a printable encoding of these binary octets e ASCII characters using base64 encoding in a format called "ASCII Armor" (see <
is defined. xref target="base64"/>).</t>
The raw 8-bit binary octet stream can be converted to a stream of printable ASCI <t>Implementations <bcp14>SHOULD</bcp14> support base64 conversions.</t>
I characters using base64 encoding, in a format called ASCII Armor (see <xref ta </section>
rget="base64"/>).</t> <section anchor="signature-only-applications">
<name>Signature-Only Applications</name>
<t>Implementations <bcp14>SHOULD</bcp14> support base64 conversions.</t> <t>OpenPGP is designed for applications that use both encryption and sig
natures, but there are a number of use cases that only require a signature-only
</section> implementation.
<section anchor="signature-only-applications"><name>Signature-Only Applications<
/name>
<t>OpenPGP is designed for applications that use both encryption and signatures,
but there are a number of use cases that only require a signature-only implemen
tation.
Although this specification requires both encryption and signatures, it is reaso nable for there to be subset implementations that are non-conformant only in tha t they omit encryption support.</t> Although this specification requires both encryption and signatures, it is reaso nable for there to be subset implementations that are non-conformant only in tha t they omit encryption support.</t>
</section>
</section>
<section anchor="data-element-formats">
<name>Data Element Formats</name>
<t>This section describes the data elements used by OpenPGP.</t>
<section anchor="scalar-numbers">
<name>Scalar Numbers</name>
<t>Scalar numbers are unsigned and always stored in big-endian format.
Using n[k] to refer to the kth octet being interpreted, the value of a 2-octet s
calar is ((n[0] &lt;&lt; 8) + n[1]).
The value of a 4-octet scalar is ((n[0] &lt;&lt; 24) + (n[1] &lt;&lt; 16) + (n[2
] &lt;&lt; 8) + n[3]).</t>
</section>
<section anchor="mpi">
<name>Multiprecision Integers</name>
<t>Multiprecision Integers (MPIs) are unsigned integers used to hold lar
ge integers such as the ones used in cryptographic calculations.</t>
<t>An MPI consists of two pieces: a 2-octet scalar that is the length of
the MPI in bits, followed by a string of octets that contain the actual integer
.</t>
<t>These octets form a big-endian number; a big-endian number can be mad
e into an MPI by prefixing it with the appropriate length.</t>
<t>Examples:</t>
<t>(Note that all numbers in the octet strings identified by square brac
kets are in hexadecimal.)</t>
</section> <ul empty="true">
</section> <li>The string of octets [00 00] forms an MPI with the value 0.</li>
<section anchor="data-element-formats"><name>Data Element Formats</name> <li>The string of octets [00 01 01] forms an MPI with the value 1.</li>
<li>The string [00 09 01 FF] forms an MPI with the value 511.</li>
<t>This section describes the data elements used by OpenPGP.</t> </ul>
<t>Additional rules:</t>
<section anchor="scalar-numbers"><name>Scalar Numbers</name> <ul>
<li>The size of an MPI is ((MPI.length + 7) / 8) + 2 octets.</li>
<t>Scalar numbers are unsigned and are always stored in big-endian format. <li>The length field of an MPI describes the length starting from its mo
Using n[k] to refer to the kth octet being interpreted, the value of a two-octet st significant non-zero bit. Thus, the MPI [00 02 01] is not formed correctly.
scalar is ((n[0] &lt;&lt; 8) + n[1]). It should be [00 01 01]. When parsing an MPI in a version 6 Key, Signature, or P
The value of a four-octet scalar is ((n[0] &lt;&lt; 24) + (n[1] &lt;&lt; 16) + ( ublic Key Encrypted Session Key (PKESK) packet, the implementation <bcp14>MUST</
n[2] &lt;&lt; 8) + n[3]).</t> bcp14> check that the encoded length matches the length starting from the most s
ignificant non-zero bit; if it doesn't match, reject the packet as malformed.</l
</section> i>
<section anchor="mpi"><name>Multiprecision Integers</name> <li>Unused bits of an MPI <bcp14>MUST</bcp14> be zero.</li>
</ul>
<t>Multiprecision integers (also called MPIs) are unsigned integers used to hold <section anchor="using-mpis-to-encode-other-data">
large integers such as the ones used in cryptographic calculations.</t> <name>Using MPIs to Encode Other Data</name>
<t>Note that in some places, MPIs are used to encode non-integer data,
<t>An MPI consists of two pieces: a two-octet scalar that is the length of the M such as an elliptic curve (EC) point (see <xref target="ec-point-wire-formats"/
PI in bits followed by a string of octets that contain the actual integer.</t> >) or an octet string of known, fixed length (see <xref target="ec-scalar-wire-f
ormats"/>). The wire representation is the same: 2 octets of length in bits coun
<t>These octets form a big-endian number; a big-endian number can be made into a ted from the first non-zero bit, followed by the smallest series of octets that
n MPI by prefixing it with the appropriate length.</t> can represent the value while stripping off any leading zero octets.</t>
</section>
<t>Examples:</t> </section>
<section anchor="key-ids-and-fingerprints">
<t>(all numbers in the octet strings identified by square brackets are in hexade <name>Key IDs and Fingerprints</name>
cimal)</t> <t>A Key ID is an 8-octet scalar that identifies a key.
<t>The string of octets [00 00] forms an MPI with the value 0.
The string of octets [00 01 01] forms an MPI with the value 1.
The string [00 09 01 FF] forms an MPI with the value of 511.</t>
<t>Additional rules:</t>
<t>The size of an MPI is ((MPI.length + 7) / 8) + 2 octets.</t>
<t>The length field of an MPI describes the length starting from its most signif
icant non-zero bit.
Thus, the MPI [00 02 01] is not formed correctly.
It should be [00 01 01].
When parsing an MPI in a v6 Key, Signature, or Public-Key Encrypted Session Key
packet, the implementation <bcp14>MUST</bcp14> check that the encoded length mat
ches the length starting from the most significant non-zero bit, and reject the
packet as malformed if not.</t>
<t>Unused bits of an MPI <bcp14>MUST</bcp14> be zero.</t>
<section anchor="using-mpis-to-encode-other-data"><name>Using MPIs to encode oth
er data</name>
<t>Note that MPIs are in some places used to encode non-integer data, such as an
elliptic curve point (see <xref target="ec-point-wire-formats"/>), or an octet
string of known, fixed length (see <xref target="ec-scalar-wire-formats"/>).
The wire representation is the same: two octets of length in bits counted from t
he first non-zero bit, followed by the smallest series of octets that can repres
ent the value while stripping off any leading zero octets.</t>
</section>
</section>
<section anchor="key-ids-and-fingerprints"><name>Key IDs and Fingerprints</name>
<t>A Key ID is an eight-octet scalar that identifies a key.
Implementations <bcp14>SHOULD NOT</bcp14> assume that Key IDs are unique. Implementations <bcp14>SHOULD NOT</bcp14> assume that Key IDs are unique.
A fingerprint is more likely to be unique than a key ID. A fingerprint is more likely to be unique than a Key ID.
The fingerprint and key ID of a key are calculated differently according to the The fingerprint and Key ID of a key are calculated differently according to the
version of the key.</t> version of the key.</t>
<t><xref target="key-ids-fingerprints"/> describes how Key IDs and Finge
<t><xref target="key-ids-fingerprints"/> describes how Key IDs and Fingerprints rprints are formed.</t>
are formed.</t> </section>
<section anchor="text">
</section> <name>Text</name>
<section anchor="text"><name>Text</name> <t>Unless otherwise specified, the character set for text is the UTF-8 <
xref target="RFC3629"/> encoding of Unicode <xref target="ISO10646"/>.</t>
<t>Unless otherwise specified, the character set for text is the UTF-8 <xref tar </section>
get="RFC3629"/> encoding of Unicode <xref target="ISO10646"/>.</t> <section anchor="time-fields">
<name>Time Fields</name>
</section> <t>A time field is an unsigned 4-octet number containing the number of s
<section anchor="time-fields"><name>Time Fields</name> econds elapsed since midnight, 1 January 1970 UTC.</t>
</section>
<t>A time field is an unsigned four-octet number containing the number of second <section anchor="keyrings">
s elapsed since midnight, 1 January 1970 UTC.</t> <name>Keyrings</name>
<t>A keyring is a collection of one or more keys in a file or database.
</section> Typically, a keyring is simply a sequential list of keys, but it may be any suit
<section anchor="keyrings"><name>Keyrings</name> able database.
It is beyond the scope of this specification to discuss the details of keyrings
<t>A keyring is a collection of one or more keys in a file or database. or other databases.</t>
Traditionally, a keyring is simply a sequential list of keys, but may be any sui </section>
table database. <section anchor="string-to-key-s2k-specifier">
It is beyond the scope of this standard to discuss the details of keyrings or ot <name>String-to-Key (S2K) Specifier</name>
her databases.</t> <t>A string-to-key (S2K) Specifier is used to convert a passphrase strin
g into a symmetric key encryption/decryption key. Passphrases requiring use of S
</section> 2K conversion are currently used in two places: to encrypt the secret part of pr
<section anchor="string-to-key-s2k-specifier"><name>String-to-Key (S2K) Specifie ivate keys and for symmetrically encrypted messages.</t>
r</name> <section anchor="s2k-types">
<name>S2K Specifier Types</name>
<t>A string-to-key (S2K) specifier type is used to convert a passphrase string i <t>There are four types of S2K Specifiers currently specified and some
nto a symmetric-key encryption/decryption key. reserved values:</t>
Passphrases requiring use of S2K conversion are currently used in two places: to <table anchor="s2k-types-registry">
encrypt the secret part of private keys, and for symmetrically encrypted messag <name>OpenPGP String-to-Key (S2K) Types Registry</name>
es.</t> <thead>
<tr>
<section anchor="s2k-types"><name>String-to-Key (S2K) Specifier Types</name> <th align="right">ID</th>
<th align="left">S2K Type</th>
<t>There are four types of S2K Specifier Types currently specified, and some res <th align="left">S2K Field Size (Octets)</th>
erved values:</t> <th align="left">Generate?</th>
<th align="left">Reference</th>
<texttable title="OpenPGP String-to-Key (S2K) Types registry" anchor="s2k-types- </tr>
registry"> </thead>
<ttcol align='right'>ID</ttcol> <tbody>
<ttcol align='left'>S2K Type</ttcol> <tr>
<ttcol align='left'>S2K field size (octets)</ttcol> <td align="right">0</td>
<ttcol align='left'>Reference</ttcol> <td align="left">Simple S2K</td>
<ttcol align='left'>Generate?</ttcol> <td align="left">2</td>
<c>0</c> <td align="left">No</td>
<c>Simple S2K</c> <td align="left"><xref target="s2k-simple"/></td>
<c>2</c> </tr>
<c><xref target="s2k-simple"/></c> <tr>
<c>No</c> <td align="right">1</td>
<c>1</c> <td align="left">Salted S2K</td>
<c>Salted S2K</c> <td align="left">10</td>
<c>10</c> <td align="left">Only when string is high entropy</td>
<c><xref target="s2k-salted"/></c> <td align="left"><xref target="s2k-salted"/></td>
<c>Only when string is high entropy</c> </tr>
<c>2</c> <tr>
<c>Reserved value</c> <td align="right">2</td>
<c>-</c> <td align="left">Reserved value</td>
<c>-</c> <td align="left">-</td>
<c>No</c> <td align="left">No</td>
<c>3</c> <td align="left"></td>
<c>Iterated and Salted S2K</c> </tr>
<c>11</c> <tr>
<c><xref target="s2k-iter-salted"/></c> <td align="right">3</td>
<c>Yes</c> <td align="left">Iterated and Salted S2K</td>
<c>4</c> <td align="left">11</td>
<c>Argon2</c> <td align="left">Yes</td>
<c>20</c> <td align="left"><xref target="s2k-iter-salted"/></td>
<c><xref target="s2k-argon2"/></c> </tr>
<c>Yes</c> <tr>
<c>100 to 110</c> <td align="right">4</td>
<c>Private/Experimental S2K</c> <td align="left">Argon2</td>
<c>-</c> <td align="left">20</td>
<c>-</c> <td align="left">Yes</td>
<c>As appropriate</c> <td align="left"><xref target="s2k-argon2"/></td>
</texttable> </tr>
<tr>
<t>These are described in the subsections below. <td align="right">100-110</td>
If the "Generate?" column is not "Yes", the S2K entry is used only for reading i <td align="left">Private or Experimental Use</td>
n backwards compatibility mode and <bcp14>SHOULD NOT</bcp14> be used to generate <td align="left">-</td>
new output.</t> <td align="left">As appropriate</td>
<td align="left"></td>
<section anchor="s2k-simple"><name>Simple S2K</name> </tr>
</tbody>
<t>This directly hashes the string to produce the key data. </table>
See below for how this hashing is done.</t> <t>The S2K Specifier Types are described in the subsections below.
If "Yes" is not present in the "Generate?" column, the S2K entry is used only fo
<figure><artwork><![CDATA[ r reading in backward-compatibility mode and <bcp14>SHOULD NOT</bcp14> be used t
o generate new output.</t>
<section anchor="s2k-simple">
<name>Simple S2K</name>
<t>Simple S2K directly hashes the string to produce the key data. Th
is hashing is done as shown below.</t>
<artwork><![CDATA[
Octet 0: 0x00 Octet 0: 0x00
Octet 1: hash algorithm Octet 1: hash algorithm
]]></artwork></figure> ]]></artwork>
<t>Simple S2K hashes the passphrase to produce the session key.
<t>Simple S2K hashes the passphrase to produce the session key.
The manner in which this is done depends on the size of the session key (which d epends on the cipher the session key will be used with) and the size of the hash algorithm's output. The manner in which this is done depends on the size of the session key (which d epends on the cipher the session key will be used with) and the size of the hash algorithm's output.
If the hash size is greater than the session key size, the high-order (leftmost) octets of the hash are used as the key.</t> If the hash size is greater than the session key size, the high-order (leftmost) octets of the hash are used as the key.</t>
<t>If the hash size is less than the key size, multiple instances of
<t>If the hash size is less than the key size, multiple instances of the hash co the hash context are created -- enough to produce the required key data. These
ntext are created --- enough to produce the required key data. instances are preloaded with 0, 1, 2, ...
These instances are preloaded with 0, 1, 2, ... octets of zeros (that is, the first instance has no preloading, the second gets
octets of zeros (that is to say, the first instance has no preloading, the secon preloaded with 1 octet of zero, the third is preloaded with 2 octets of zeros, a
d gets preloaded with 1 octet of zero, the third is preloaded with two octets of nd so forth).</t>
zeros, and so forth).</t> <t>As the data is hashed, it is given independently to each hash con
text. Since the contexts have been initialized differently, they will each produ
<t>As the data is hashed, it is given independently to each hash context. ce a different hash output. Once the passphrase is hashed, the output data from
Since the contexts have been initialized differently, they will each produce dif the multiple hashes is concatenated, first hash leftmost, to produce the key dat
ferent hash output. a, and any excess octets on the right are discarded.</t>
Once the passphrase is hashed, the output data from the multiple hashes is conca </section>
tenated, first hash leftmost, to produce the key data, with any excess octets on <section anchor="s2k-salted">
the right discarded.</t> <name>Salted S2K</name>
<t>Salted S2K includes a "salt" value in the S2K Specifier -- some a
</section> rbitrary data -- that gets hashed along with the passphrase string to help preve
<section anchor="s2k-salted"><name>Salted S2K</name> nt dictionary attacks.</t>
<artwork><![CDATA[
<t>This includes a "salt" value in the S2K specifier --- some arbitrary data ---
that gets hashed along with the passphrase string, to help prevent dictionary a
ttacks.</t>
<figure><artwork><![CDATA[
Octet 0: 0x01 Octet 0: 0x01
Octet 1: hash algorithm Octet 1: hash algorithm
Octets 2-9: 8-octet salt value Octets 2-9: 8-octet salt value
]]></artwork></figure> ]]></artwork>
<t>Salted S2K is exactly like Simple S2K, except that the input to t
<t>Salted S2K is exactly like Simple S2K, except that the input to the hash func he hash function(s) consists of the 8 octets of salt from the S2K Specifier, fol
tion(s) consists of the 8 octets of salt from the S2K specifier, followed by the lowed by the passphrase.</t>
passphrase.</t> </section>
<section anchor="s2k-iter-salted">
</section> <name>Iterated and Salted S2K</name>
<section anchor="s2k-iter-salted"><name>Iterated and Salted S2K</name> <t>Iterated and Salted S2K includes both a salt and an octet count.
The salt is combined with the passphrase, and the resulting value is repeated an
<t>This includes both a salt and an octet count. d then hashed.
The salt is combined with the passphrase and the resulting value is repeated and
then hashed.
This further increases the amount of work an attacker must do to try dictionary attacks.</t> This further increases the amount of work an attacker must do to try dictionary attacks.</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
Octet 0: 0x03 Octet 0: 0x03
Octet 1: hash algorithm Octet 1: hash algorithm
Octets 2-9: 8-octet salt value Octets 2-9: 8-octet salt value
Octet 10: count, a one-octet, coded value Octet 10: count; a 1-octet coded value
]]></artwork></figure> ]]></artwork>
<t>The count is coded into a 1-octet number using the following form
<t>The count is coded into a one-octet number using the following formula:</t> ula:</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
#define EXPBIAS 6 #define EXPBIAS 6
count = ((Int32)16 + (c & 15)) << ((c >> 4) + EXPBIAS); count = ((Int32)16 + (c & 15)) << ((c >> 4) + EXPBIAS);
]]></artwork></figure> ]]></artwork>
<t>The above formula is described in <xref target="C99"/>, where "In
<t>The above formula is in <xref target="C99"/>, where "Int32" is a type for a 3 t32" is a type for a 32-bit integer, and the variable "c" is the coded count, oc
2-bit integer, and the variable "c" is the coded count, Octet 10.</t> tet 10.</t>
<t>Iterated and Salted S2K hashes the passphrase and salt data multi
<t>Iterated-Salted S2K hashes the passphrase and salt data multiple times. ple times.
The total number of octets to be hashed is specified in the encoded count in the The total number of octets to be hashed is specified in the encoded count in the
S2K specifier. S2K Specifier.
Note that the resulting count value is an octet count of how many octets will be Note that the resulting count value is an octet count of how many oct
hashed, not an iteration count.</t> ets will be hashed, not an iteration count.</t>
<t>Initially, one or more hash contexts are set up as with the other S2K algorit
hms, depending on how many octets of key data are needed.
Then the salt, followed by the passphrase data, is repeatedly processed as input
to each hash context until the number of octets specified by the octet count ha
s been hashed.
The input is truncated to the octet count, except if the octet count is less tha
n the initial isize of the salt plus passphrase.
That is, at least one copy of the full salt plus passphrase will be provided as
input to each hash context regardless of the octet count.
After the hashing is done, the key data is produced from the hash digest(s) as w
ith the other S2K algorithms.</t>
</section>
<section anchor="s2k-argon2"><name>Argon2</name>
<t>This S2K method hashes the passphrase using Argon2, specified in <xref target <t>Initially, one or more hash contexts are set up the same as the o
="RFC9106"/>. ther S2K algorithms, depending on how many octets of key data are needed. Then t
This provides memory-hardness, further protecting the passphrase against brute-f he salt, followed by the passphrase data, is repeatedly processed as input to ea
orce attacks.</t> ch hash context until the number of octets specified by the octet count has been
hashed. The input is truncated to the octet count, except if the octet count is
less than the initial size of the salt plus passphrase. That is, at least one c
opy of the full salt plus passphrase will be provided as input to each hash cont
ext regardless of the octet count. After the hashing is done, the key data is pr
oduced from the hash digest(s), which is the same way it is produced for the oth
er S2K algorithms.</t>
</section>
<section anchor="s2k-argon2">
<name>Argon2</name>
<t>This S2K method hashes the passphrase using Argon2, as specified
in <xref target="RFC9106"/>.
This provides memory hardness, further protecting the passphrase agai
nst brute-force attacks.</t>
<figure><artwork><![CDATA[ <artwork><![CDATA[
Octet 0: 0x04 Octet 0: 0x04
Octets 1-16: 16-octet salt value Octets 1-16: 16-octet salt value
Octet 17: one-octet number of passes t Octet 17: 1-octet number of passes t
Octet 18: one-octet degree of parallelism p Octet 18: 1-octet degree of parallelism p
Octet 19: one-octet encoded_m, specifying the exponent of the memory si Octet 19: 1-octet encoded_m, specifying the exponent of
ze the memory size
]]></artwork></figure> ]]></artwork>
<t>The salt <bcp14>SHOULD</bcp14> be unique for each passphrase.</t>
<t>The salt <bcp14>SHOULD</bcp14> be unique for each passphrase.</t> <t>The number of passes t and the degree of parallelism p <bcp14>MUS
T</bcp14> be non-zero.</t>
<t>The number of passes t and the degree of parallelism p <bcp14>MUST</bcp14> be <t>The memory size m is 2<sup><tt>encoded_m</tt></sup> kibibytes (Ki
non-zero.</t> B) of RAM.
The encoded memory size <bcp14>MUST</bcp14> be a value from 3+ceil(log<sub>2</su
<t>The memory size m is 2**encoded_m kibibytes of RAM. b>(p)) to 31, such that the decoded memory size m is a value from 8*p to 2<sup>3
The encoded memory size <bcp14>MUST</bcp14> be a value from 3+ceil(log_2(p)) to 1</sup>. Note that memory-hardness size is indicated in KiB, not octets.</t>
31, such that the decoded memory size m is a value from 8*p to 2**31. <t>Argon2 is invoked with the passphrase as P, the salt as S, the va
Note that memory-hardness size is indicated in kibibytes (KiB), not octets.</t> lues of t, p, and m as described above, the required key size as the tag length
T, 0x13 as the version v, and Argon2id as the type.</t>
<t>Argon2 is invoked with the passphrase as P, the salt as S, the values of t, p <t>For the recommended values of t, p, and m, see <xref section="4"
and m as described above, the required key size as the tag length T, 0x13 as th sectionFormat="of" target="RFC9106"/>.
e version v, and Argon2id as the type.</t> If the recommended value of m for a given application is not a power of 2, it is
<bcp14>RECOMMENDED</bcp14> to round up to the next power of 2 if the resulting
<t>For the recommended values of t, p and m, see <xref section="4" sectionFormat performance would be acceptable; otherwise, round down (keeping in mind that m m
="of" target="RFC9106"/>. ust be at least 8*p).</t>
If the recommended value of m for a given application is not a power of 2, it is <t>As an example, with the first recommended option (t=1, p=4, m=2<s
<bcp14>RECOMMENDED</bcp14> to round up to the next power of 2 if the resulting up>21</sup>), the full S2K Specifier would be:</t>
performance would be acceptable, and round down otherwise (keeping in mind that <artwork><![CDATA[
m must be at least 8*p).</t>
<t>As an example, with the first recommended option (t=1, p=4, m=2**21), the ful
l S2K specifier would be:</t>
<figure><artwork><![CDATA[
04 XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX 04 XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
XX 01 04 15 XX 01 04 15
]]></artwork></figure> ]]></artwork>
<t>where XX represents a random octet of salt.</t>
<t>(where XX represents a random octet of salt).</t> </section>
</section>
</section> <section anchor="s2k-usage-octet">
</section> <name>S2K Usage</name>
<section anchor="s2k-usage-octet"><name>String-to-Key Usage</name> <t>Simple S2K and Salted S2K Specifiers can be brute-forced when used
with a low-entropy string, such as those typically provided by users.
<t>Simple S2K and Salted S2K specifiers can be brute-forced when used with a low In addition, the usage of Simple S2K can lead to key and initialization vector (
-entropy string, such as those typically provided by users. IV) reuse (see <xref target="skesk"/>).
In addition, the usage of Simple S2K can lead to key and IV reuse (see <xref tar Therefore, when generating an S2K Specifier, an implementation <bcp14>MUST NOT</
get="skesk"/>). bcp14> use Simple S2K.
Therefore, when generating an S2K specifier, an implementation <bcp14>MUST NOT</ Furthermore, an implementation <bcp14>SHOULD NOT</bcp14> generate a Salted S2K u
bcp14> use Simple S2K. nless the implementation knows that the input string is high entropy (for exampl
Furthermore, an implementation <bcp14>SHOULD NOT</bcp14> generate a Salted S2K u e, it generated the string itself using a known good source of randomness).</t>
nless the implementation knows that the input string is high-entropy (for exampl <t>It is <bcp14>RECOMMENDED</bcp14> that implementations use Argon2.
e, it generated the string itself using a known-good source of randomness).</t>
<t>It is <bcp14>RECOMMENDED</bcp14> that implementations use Argon2.
If Argon2 is not available, Iterated and Salted S2K <bcp14>MAY</bcp14> be used i f care is taken to use a high octet count and a strong passphrase. If Argon2 is not available, Iterated and Salted S2K <bcp14>MAY</bcp14> be used i f care is taken to use a high octet count and a strong passphrase.
However, this method does not provide memory-hardness, unlike Argon2.</t> However, this method does not provide memory hardness, unlike Argon2.</t>
<section anchor="secret-key-encryption">
<section anchor="secret-key-encryption"><name>Secret-Key Encryption</name> <name>Secret Key Encryption</name>
<t>The first octet following the public key material in a Secret Key
<t>The first octet following the public key material in a secret key packet (<xr packet (<xref target="secret-key-packet-formats"/>) indicates whether and how t
ef target="secret-key-packet-formats"/>) indicates whether and how the secret ke he secret key material is passphrase protected.
y material is passphrase-protected.
This first octet is known as the "S2K usage octet".</t> This first octet is known as the "S2K usage octet".</t>
<t>If the S2K usage octet is zero, the secret key data is unprotecte
<t>If S2K usage octet is zero, the secret key data is unprotected. d.
If it is non-zero, it describes how to use a passphrase to unlock the secret key .</t> If it is non-zero, it describes how to use a passphrase to unlock the secret key .</t>
<t>Implementations predating <xref target="RFC2440"/> indicated a pr
<t>Implementations predating <xref target="RFC2440"/> indicated a protected key otected key by storing a Symmetric Cipher Algorithm ID (see <xref target="symmet
by storing a symmetric cipher algorithm ID (see <xref target="symmetric-algos"/> ric-algos"/>) in the S2K usage octet.
) in the S2K usage octet.
In this case, the MD5 hash function was always used to convert the passphrase to a key for the specified cipher algorithm.</t> In this case, the MD5 hash function was always used to convert the passphrase to a key for the specified cipher algorithm.</t>
<t>Later implementations indicate a protected secret key by storing
one of the special values 253 (AEAD), 254 (CFB), or 255 (MalleableCFB) in the S2
K usage octet. The S2K usage octet is then followed immediately by a set of fiel
ds that describe how to convert a passphrase to a symmetric key that can unlock
the secret material, plus other parameters relevant to the type of encryption us
ed.</t>
<t>The wire format fields also differ based on the version of the en
closing OpenPGP packet.
The table below, indexed by the S2K usage octet, summarizes the speci
fics described in <xref target="secret-key-packet-formats"/>.</t>
<t>Later implementations indicate a protected secret key by storing a special va <t>In the table below, <tt>check(x)</tt> means the "2-octet checksum
lue 253 (AEAD), 254 (CFB), or 255 (MalleableCFB) in the S2K usage octet. ", which is the sum of all octets in x mod 65536. The <tt>info</tt> and <tt>pack
The S2K usage octet is then followed immediately by a set of fields that describ etprefix</tt> parameters are described in detail in <xref target="secret-key-pac
e how to convert a passphrase to a symmetric key that can unlock the secret mate ket-formats"/>. Note that the "Generate?" column header has been shortened to "
rial, plus other parameters relevant to the type of encryption used.</t> Gen?" here.</t>
<table anchor="secret-key-protection-registry">
<t>The wire format fields also differ based on the version of the enclosing Open <name>OpenPGP Secret Key Encryption (S2K Usage Octet) Registry</na
PGP packet. me>
The table below, indexed by S2K usage octet, summarizes the specifics described <thead>
in <xref target="secret-key-packet-formats"/>.</t> <tr>
<th align="left">S2K Usage Octet</th>
<t>In the table below, <spanx style="verb">check(x)</spanx> means the "2-octet c <th align="left">Shorthand</th>
hecksum" meaning the sum of all octets in x mod 65536. <th align="left">Encryption Parameter Fields</th>
The <spanx style="verb">info</spanx> and <spanx style="verb">packetprefix</spanx <th align="left">Encryption</th>
> parameters are described in detail in <xref target="secret-key-packet-formats" <th align="left">Gen?</th>
/>.</t> </tr>
</thead>
<texttable title="OpenPGP Secret Key Encryption (S2K Usage Octet) registry" anch <tbody>
or="secret-key-protection-registry"> <tr>
<ttcol align='left'>S2K usage octet</ttcol> <td align="left">0</td>
<ttcol align='left'>Shorthand</ttcol> <td align="left">Unprotected</td>
<ttcol align='left'>Encryption parameter fields</ttcol> <td align="left">-</td>
<ttcol align='left'>Encryption</ttcol> <td align="left"> <strong>v3 or v4 keys:</strong> [cleartext s
<ttcol align='left'>Generate?</ttcol> ecrets || check(secrets)] <br/>
<c>0</c> <strong>v6 keys:</strong> [cleartext secrets]
<c>Unprotected</c> </td>
<c>-</c> <td align="left">Yes</td>
<c><strong>v3 or v4 keys:</strong> [cleartext secrets || check(secrets)] < </tr>
br /> <strong>v6 keys:</strong> [cleartext secrets]</c> <tr>
<c>Yes</c> <td align="left">Known symmetric cipher algo ID (see <xref tar
<c>Known symmetric cipher algo ID (see <xref target="symmetric-algos"/>)</ get="symmetric-algos"/>)</td>
c> <td align="left">LegacyCFB</td>
<c>LegacyCFB</c> <td align="left">IV</td>
<c>IV</c> <td align="left">CFB(MD5(passphrase), secrets || check(secrets
<c>CFB(MD5(passphrase), secrets || check(secrets))</c> ))</td>
<c>No</c> <td align="left">No</td>
<c>253</c> </tr>
<c>AEAD</c> <tr>
<c>params-length (<strong>v6-only</strong>), cipher-algo, AEAD-mode, S2K-s <td align="left">253</td>
pecifier-length (<strong>v6-only</strong>), S2K-specifier, nonce</c> <td align="left">AEAD</td>
<c>AEAD(HKDF(S2K(passphrase), info), secrets, packetprefix)</c> <td align="left">params-length (<strong>v6-only</strong>), cip
<c>Yes</c> her-algo, AEAD-mode, S2K-specifier-length (<strong>v6-only</strong>), S2K-specif
<c>254</c> ier, nonce
<c>CFB</c> </td>
<c>params-length (<strong>v6-only</strong>), cipher-algo, S2K-specifier-le <td align="left">AEAD(HKDF(S2K(passphrase), info), secrets, pa
ngth (<strong>v6-only</strong>), S2K-specifier, IV</c> cketprefix)</td>
<c>CFB(S2K(passphrase), secrets || SHA1(secrets))</c> <td align="left">Yes</td>
<c>Yes</c> </tr>
<c>255</c> <tr>
<c>MalleableCFB</c> <td align="left">254</td>
<c>cipher-algo, S2K-specifier, IV</c> <td align="left">CFB</td>
<c>CFB(S2K(passphrase), secrets || check(secrets))</c> <td align="left">params-length (<strong>v6-only</strong>), cip
<c>No</c> her-algo, S2K-specifier-length (<strong>v6-only</strong>), S2K-specifier, IV</td
</texttable> >
<td align="left">CFB(S2K(passphrase), secrets || SHA1(secrets)
<t>When emitting a secret key (with or without passphrase-protection) an impleme )</td>
ntation <bcp14>MUST</bcp14> only produce data from a row with "Generate?" marked <td align="left">Yes</td>
as "Yes". </tr>
Each row with "Generate?" marked as "No" is described for backward compatibility <tr>
(for reading v4 and earlier keys only), and <bcp14>MUST NOT</bcp14> be used to <td align="left">255</td>
generate new output. <td align="left">MalleableCFB</td>
<td align="left">cipher-algo, S2K-specifier, IV</td>
<td align="left">CFB(S2K(passphrase), secrets || check(secrets
))</td>
<td align="left">No</td>
</tr>
</tbody>
</table>
<t>When emitting a secret key (with or without passphrase protection
), an implementation <bcp14>MUST</bcp14> only produce data from a row with "Gene
rate?" marked as "Yes".
Each row with "Generate?" marked as "No" is described for backward compatibility
(for reading version 4 and earlier keys only) and <bcp14>MUST NOT</bcp14> be us
ed to generate new output.
Version 6 secret keys using these formats <bcp14>MUST</bcp14> be rejected.</t> Version 6 secret keys using these formats <bcp14>MUST</bcp14> be rejected.</t>
<t>Note that compared to a version 4 secret key, the parameters of a
<t>Note that compared to a version 4 secret key, the parameters of a passphrase- passphrase-protected version 6 secret key are stored with an additional pair of
protected version 6 secret key are stored with an additional pair of length coun length counts, each of which is 1 octet wide.</t>
ts, each of which is one octet wide.</t> <t>Argon2 is only used with Authenticated Encryption with Associated
Data (AEAD) (S2K usage octet 253).
<t>Argon2 is only used with AEAD (S2K usage octet 253). An implementation <bcp14>MUST NOT</bcp14> create and <bcp14>MUST</bcp14> reject
An implementation <bcp14>MUST NOT</bcp14> create and <bcp14>MUST</bcp14> reject as malformed any Secret Key packet where the S2K usage octet is not AEAD (253) a
as malformed any secret key packet where the S2K usage octet is not AEAD (253) a nd the S2K Specifier Type is Argon2.</t>
nd the S2K specifier type is Argon2.</t> </section>
<section anchor="symmetric-key-message-encryption">
</section> <name>Symmetric Key Message Encryption</name>
<section anchor="symmetric-key-message-encryption"><name>Symmetric-Key Message E <t>OpenPGP can create a Symmetric Key Encrypted Session Key (SKESK)
ncryption</name> packet at the front of a message.
This is used to allow S2K Specifiers to be used for the passphrase co
<t>OpenPGP can create a Symmetric-key Encrypted Session Key (ESK) packet at the nversion or to create messages with a mix of SKESK packets and PKESK packets. Th
front of a message. is allows a message to be decrypted with either a passphrase or a public key pai
This is used to allow S2K specifiers to be used for the passphrase conversion or r.</t>
to create messages with a mix of symmetric-key ESKs and public-key ESKs. <t>Implementations predating <xref target="RFC2440"/> always used th
This allows a message to be decrypted either with a passphrase or a public-key p e International Data Encryption Algorithm (IDEA) with Simple S2K conversion when
air.</t> encrypting a message with a symmetric algorithm;
see <xref target="sed"/>. IDEA <bcp14>MUST NOT</bcp14> be generated but <bcp14>M
<t>Implementations predating <xref target="RFC2440"/> always used IDEA with Simp AY</bcp14> be consumed for backward compatibility.</t>
le string-to-key conversion when encrypting a message with a symmetric algorithm </section>
. </section>
See <xref target="sed"/>. </section>
This <bcp14>MUST NOT</bcp14> be generated, but <bcp14>MAY</bcp14> be consumed fo </section>
r backward-compatibility.</t> <section anchor="packet-syntax">
<name>Packet Syntax</name>
</section> <t>This section describes the packets used by OpenPGP.</t>
</section> <section anchor="overview">
</section> <name>Overview</name>
</section> <t>An OpenPGP Message is constructed from a number of records that are t
<section anchor="packet-syntax"><name>Packet Syntax</name> ypically called packets.
A packet is a chunk of data that has a Type ID specifying its meaning.
<t>This section describes the packets used by OpenPGP.</t> An OpenPGP Message, keyring, certificate, detached signature, and so forth consi
sts of a number of packets.
<section anchor="overview"><name>Overview</name>
<t>An OpenPGP message is constructed from a number of records that are tradition
ally called packets.
A packet is a chunk of data that has a type ID specifying its meaning.
An OpenPGP message, keyring, certificate, detached signature, and so forth consi
sts of a number of packets.
Some of those packets may contain other OpenPGP packets (for example, a compress ed data packet, when uncompressed, contains OpenPGP packets).</t> Some of those packets may contain other OpenPGP packets (for example, a compress ed data packet, when uncompressed, contains OpenPGP packets).</t>
<t>Each packet consists of a packet header, followed by the packet body.
<t>Each packet consists of a packet header, followed by the packet body.
The packet header is of variable length.</t> The packet header is of variable length.</t>
<t>When handling a stream of packets, the length information in each pac
<t>When handling a stream of packets, the length information in each packet head ket header is the canonical source of packet boundaries.
er is the canonical source of packet boundaries.
An implementation handling a packet stream that wants to find the next packet <b cp14>MUST</bcp14> look for it at the precise offset indicated in the previous pa cket header.</t> An implementation handling a packet stream that wants to find the next packet <b cp14>MUST</bcp14> look for it at the precise offset indicated in the previous pa cket header.</t>
<t>Additionally, some packets contain internal length indicators (for ex
<t>Additionally, some packets contain internal length indicators (for example, a ample, a subfield within the packet).
subfield within the packet).
In the event that a subfield length indicator within a packet implies inclusion of octets outside the range indicated in the packet header, a parser <bcp14>MUST </bcp14> abort without writing outside the indicated range and <bcp14>MUST</bcp1 4> treat the packet as malformed and unusable.</t> In the event that a subfield length indicator within a packet implies inclusion of octets outside the range indicated in the packet header, a parser <bcp14>MUST </bcp14> abort without writing outside the indicated range and <bcp14>MUST</bcp1 4> treat the packet as malformed and unusable.</t>
<t>An implementation <bcp14>MUST NOT</bcp14> interpret octets outside th
<t>An implementation <bcp14>MUST NOT</bcp14> interpret octets outside the range e range indicated in the packet header as part of the contents of the packet.</t
indicated in the packet header as part of the contents of the packet.</t> >
</section>
</section> <section anchor="packet-headers">
<section anchor="packet-headers"><name>Packet Headers</name> <name>Packet Headers</name>
<t>The first octet of the packet denotes the format of the rest of the h
<t>The first octet of the packet denotes the format of the rest of the header, a eader, and it encodes the Packet Type ID, indicating the type of the packet (see
nd encodes the Packet Type ID, indicating the type of the packet (see <xref targ <xref target="packet-types"/>). The remainder of the packet header is the lengt
et="packet-types"/>). h of the packet.</t>
The remainder of the packet header is the length of the packet.</t> <t>There are two packet formats: 1) the (current) OpenPGP packet format
specified by this document and its predecessors <xref target="RFC4880"/> and <xr
<t>There are two packet formats, the (current) OpenPGP packet format specified b ef target="RFC2440"/> and 2) the Legacy packet format as used by implementations
y this document and its predecessors <xref target="RFC4880"/> and <xref target=" predating any IETF specification of OpenPGP.</t>
RFC2440"/>, and the Legacy packet format as used by implementations predating an <t>Note that the most significant bit is the leftmost bit, called "bit 7
y IETF specification of the protocol.</t> ".
<t>Note that the most significant bit is the leftmost bit, called bit 7.
A mask for this bit is 0x80 in hexadecimal.</t> A mask for this bit is 0x80 in hexadecimal.</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[ +---------------+
┌───────────────┐ Encoded Packet Type ID: |7 6 5 4 3 2 1 0|
Encoded Packet Type ID: │7 6 5 4 3 2 1 0│ +---------------+
└───────────────┘
OpenPGP format: OpenPGP format:
Bit 7 -- always one Bit 7 -- always one
Bit 6 -- always one Bit 6 -- always one
Bits 5 to 0 -- packet type ID Bits 5 to 0 -- Packet Type ID
Legacy format: Legacy format:
Bit 7 -- always one Bit 7 -- always one
Bit 6 -- always zero Bit 6 -- always zero
Bits 5 to 2 -- packet type ID Bits 5 to 2 -- Packet Type ID
Bits 1 to 0 -- length-type Bits 1 to 0 -- length-type
]]></artwork></figure> ]]></artwork>
<t>Bit 6 of the first octet of the packet header indicates whether the p
<t>Bit 6 of the first octet of the packet header indicates whether the packet is acket is encoded in the OpenPGP or Legacy packet format.
encoded in the OpenPGP or Legacy packet format.
The Legacy packet format <bcp14>MAY</bcp14> be used when consuming packets to fa cilitate interoperability and accessing archived data. The Legacy packet format <bcp14>MAY</bcp14> be used when consuming packets to fa cilitate interoperability and accessing archived data.
The Legacy packet format <bcp14>SHOULD NOT</bcp14> be used to generate new data, The Legacy packet format <bcp14>SHOULD NOT</bcp14> be used to generate new data,
unless the recipient is known to only support the Legacy packet format. unless the recipient is known to only support the Legacy packet format. This la
This latter case is extremely unlikely, as the Legacy packet format was obsolete tter case is extremely unlikely, as the Legacy packet format was obsoleted by <x
d by <xref target="RFC2440"/> in 1998.</t> ref target="RFC2440"/> in 1998.</t>
<t>An implementation that consumes and redistributes pre-existing OpenPG
<t>An implementation that consumes and re-distributes pre-existing OpenPGP data P data (such as Transferable Public Keys) may encounter packets framed with the
(such as Transferable Public Keys) may encounter packets framed with the Legacy Legacy packet format. Such an implementation <bcp14>MAY</bcp14> either redistrib
packet format. ute these packets in their Legacy format or transform them to the current OpenPG
Such an implementation <bcp14>MAY</bcp14> either re-distribute these packets in P packet format before redistribution.</t>
their Legacy format, or transform them to the current OpenPGP packet format befo <t>Note that Legacy format headers only have 4 bits for the Packet Type
re re-distribution.</t> ID and hence can only encode Packet Type IDs less than 16, whereas the OpenPGP f
ormat headers can encode IDs as great as 63.</t>
<t>Note that Legacy format headers only have 4 bits for the packet type ID, and <section anchor="openpgp-packet-format">
hence can only encode packet type IDs less than 16, whereas the OpenPGP format h <name>OpenPGP Format Packet Lengths</name>
eaders can encode IDs as great as 63.</t> <t>OpenPGP format packets have four possible ways of encoding length:<
/t>
<section anchor="openpgp-packet-format"><name>OpenPGP Format Packet Lengths</nam <ol spacing="normal" type="1"><li>
e> <t>A 1-octet Body Length header encodes packet lengths of up to 19
1 octets.</t>
<t>OpenPGP format packets have four possible ways of encoding length:</t> </li>
<li>
<t><list style="numbers"> <t>A 2-octet Body Length header encodes packet lengths of 192 to 8
<t>A one-octet Body Length header encodes packet lengths of up to 191 octets.< 383 octets.</t>
/t> </li>
<t>A two-octet Body Length header encodes packet lengths of 192 to 8383 octets <li>
.</t> <t>A 5-octet Body Length header encodes packet lengths of up to 4,
<t>A five-octet Body Length header encodes packet lengths of up to 4,294,967,2 294,967,295 (0xFFFFFFFF) octets in length.
95 (0xFFFFFFFF) octets in length. (This actually encodes a 4-octet scalar number.)</t>
(This actually encodes a four-octet scalar number.)</t> </li>
<t>When the length of the packet body is not known in advance by the issuer, P <li>
artial Body Length headers encode a packet of indeterminate length, effectively <t>When the length of the packet body is not known in advance by t
making it a stream.</t> he issuer, Partial Body Length headers encode a packet of indeterminate length,
</list></t> effectively making it a stream.</t>
</li>
<section anchor="one-octet-lengths"><name>One-Octet Lengths</name> </ol>
<section anchor="one-octet-lengths">
<t>A one-octet Body Length header encodes a length of 0 to 191 octets. <name>1-Octet Lengths</name>
This type of length header is recognized because the one octet value is less tha <t>A 1-octet Body Length header encodes a length of 0 to 191 octets.
n 192. This type of length header is recognized because the 1-octet value is less than
192.
The body length is equal to:</t> The body length is equal to:</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
bodyLen = 1st_octet; bodyLen = 1st_octet;
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="two-octet-lengths">
<section anchor="two-octet-lengths"><name>Two-Octet Lengths</name> <name>2-Octet Lengths</name>
<t>A 2-octet Body Length header encodes a length of 192 to 8383 octe
<t>A two-octet Body Length header encodes a length of 192 to 8383 octets. ts.
It is recognized because its first octet is in the range 192 to 223. It is recognized because its first octet is in the range 192 to 223.
The body length is equal to:</t> The body length is equal to:</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
bodyLen = ((1st_octet - 192) << 8) + (2nd_octet) + 192 bodyLen = ((1st_octet - 192) << 8) + (2nd_octet) + 192
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="five-octet-lengths">
<section anchor="five-octet-lengths"><name>Five-Octet Lengths</name> <name>5-Octet Lengths</name>
<t>A 5-octet Body Length header consists of a single octet holding t
<t>A five-octet Body Length header consists of a single octet holding the value he value 255, followed by a 4-octet scalar. The body length is equal to:</t>
255, followed by a four-octet scalar. <artwork><![CDATA[
The body length is equal to:</t>
<figure><artwork><![CDATA[
bodyLen = (2nd_octet << 24) | (3rd_octet << 16) | bodyLen = (2nd_octet << 24) | (3rd_octet << 16) |
(4th_octet << 8) | 5th_octet (4th_octet << 8) | 5th_octet
]]></artwork></figure> ]]></artwork>
<t>This basic set of 1-octet, 2-octet, and 5-octet lengths is also u
<t>This basic set of one, two, and five-octet lengths is also used internally to sed internally to some packets.</t>
some packets.</t> </section>
<section anchor="partial-body-lengths">
</section> <name>Partial Body Lengths</name>
<section anchor="partial-body-lengths"><name>Partial Body Lengths</name> <t>A Partial Body Length header is 1 octet long and encodes the leng
th of only part of the data packet.
<t>A Partial Body Length header is one octet long and encodes the length of only
part of the data packet.
This length is a power of 2, from 1 to 1,073,741,824 (2 to the 30th power). This length is a power of 2, from 1 to 1,073,741,824 (2 to the 30th power).
It is recognized by its one octet value that is greater than or equal to 224, an d less than 255. It is recognized by its 1-octet value that is greater than or equal to 224, and less than 255.
The Partial Body Length is equal to:</t> The Partial Body Length is equal to:</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
partialBodyLen = 1 << (1st_octet & 0x1F); partialBodyLen = 1 << (1st_octet & 0x1F);
]]></artwork></figure> ]]></artwork>
<t>Each Partial Body Length header is followed by a portion of the p
<t>Each Partial Body Length header is followed by a portion of the packet body d acket body data;
ata. the Partial Body Length header specifies this portion's length.
The Partial Body Length header specifies this portion's length. Another length header (1-octet, 2-octet, 5-octet, or partial) follows that porti
Another length header (one octet, two-octet, five-octet, or partial) follows tha on.
t portion.
The last length header in the packet <bcp14>MUST NOT</bcp14> be a Partial Body L ength header. The last length header in the packet <bcp14>MUST NOT</bcp14> be a Partial Body L ength header.
Partial Body Length headers may only be used for the non-final parts of the pack et.</t> Partial Body Length headers may only be used for the non-final parts of the pack et.</t>
<t>Note also that the last Body Length header can be a zero-length h
<t>Note also that the last Body Length header can be a zero-length header.</t> eader.</t>
<t>An implementation <bcp14>MAY</bcp14> use Partial Body Lengths for
<t>An implementation <bcp14>MAY</bcp14> use Partial Body Lengths for data packet data packets, whether they are literal, compressed, or encrypted. The first par
s, be they literal, compressed, or encrypted. tial length <bcp14>MUST</bcp14> be at least 512 octets long.
The first partial length <bcp14>MUST</bcp14> be at least 512 octets long.
Partial Body Lengths <bcp14>MUST NOT</bcp14> be used for any other packet types. </t> Partial Body Lengths <bcp14>MUST NOT</bcp14> be used for any other packet types. </t>
</section>
</section> </section>
</section> <section anchor="legacy-packet-format">
<section anchor="legacy-packet-format"><name>Legacy Format Packet Lengths</name> <name>Legacy Format Packet Lengths</name>
<t>A zero in bit 6 of the first octet of the packet indicates a Legacy
<t>A zero in bit 6 of the first octet of the packet indicates a Legacy packet fo packet format.
rmat.
Bits 1 and 0 of the first octet of a Legacy packet are the "length-type" field. Bits 1 and 0 of the first octet of a Legacy packet are the "length-type" field.
The meaning of the length-type in Legacy format packets is:</t> The meaning of length-type in Legacy format packets is as follows:</t>
<dl>
<dl> <dt>0</dt>
<dt>0</dt> <dd>The packet has a 1-octet length. The header is 2 octets long.
<dd> </dd>
<t>The packet has a one-octet length. <dt>1</dt>
The header is 2 octets long.</t> <dd>The packet has a 2-octet length. The header is 3 octets long.
</dd> </dd>
<dt>1</dt> <dt>2</dt>
<dd> <dd>The packet has a 4-octet length. The header is 5 octets long.
<t>The packet has a two-octet length. </dd>
The header is 3 octets long.</t> <dt>3</dt>
</dd> <dd>The packet is of indeterminate length.
<dt>2</dt>
<dd>
<t>The packet has a four-octet length.
The header is 5 octets long.</t>
</dd>
<dt>3</dt>
<dd>
<t>The packet is of indeterminate length.
The header is 1 octet long, and the implementation must determine how long the p acket is. The header is 1 octet long, and the implementation must determine how long the p acket is.
If the packet is in a file, this means that the packet extends until the end of the file. If the packet is in a file, it means that the packet extends until the end of th e file.
The OpenPGP format headers have a mechanism for precisely encoding data of indet erminate length. The OpenPGP format headers have a mechanism for precisely encoding data of indet erminate length.
An implementation <bcp14>MUST NOT</bcp14> generate a Legacy format packet with i ndeterminate length. An implementation <bcp14>MUST NOT</bcp14> generate a Legacy format packet with i ndeterminate length.
An implementation <bcp14>MAY</bcp14> interpret an indeterminate length Legacy fo An implementation <bcp14>MAY</bcp14> interpret an indeterminate length Legacy fo
rmat packet in order to deal with historic data, or data generated by a legacy s rmat packet in order to deal with historic data or data generated by a legacy sy
ystem that predates support for <xref target="RFC2440"/>.</t> stem that predates support for <xref target="RFC2440"/>.
</dd> </dd>
</dl> </dl>
</section>
</section> <section anchor="packet-length-examples">
<section anchor="packet-length-examples"><name>Packet Length Examples</name> <name>Packet Length Examples</name>
<t>These examples show ways that OpenPGP format packets might encode t
<t>These examples show ways that OpenPGP format packets might encode the packet he packet body lengths.</t>
body lengths.</t> <ul>
<li>A packet body with length 100 may have its length encoded in one o
<t>A packet body with length 100 may have its length encoded in one octet: 0x64. ctet: 0x64.
This is followed by 100 octets of data.</t> This is followed by 100 octets of data.</li>
<li>A packet body with length 1723 may have its length encoded in two
<t>A packet body with length 1723 may have its length encoded in two octets: 0xC octets: 0xC5, 0xFB.
5, 0xFB. This header is followed by the 1723 octets of data.</li>
This header is followed by the 1723 octets of data.</t> <li>A packet body with length 100000 may have its length encoded in five octets:
0xFF, 0x00, 0x01, 0x86, 0xA0.</li>
<t>A packet body with length 100000 may have its length encoded in five octets: </ul>
0xFF, 0x00, 0x01, 0x86, 0xA0.</t> <t>It might also be encoded in the following octet stream:</t>
<ul>
<t>It might also be encoded in the following octet stream: 0xEF, first 32768 oct <li>0xEF, first 32768 octets of data;</li>
ets of data; 0xE1, next two octets of data; 0xE0, next one octet of data; 0xF0, <li>0xE1, next 2 octets of data;</li>
next 65536 octets of data; 0xC5, 0xDD, last 1693 octets of data. <li>0xE0, next 1 octet of data;</li>
This is just one possible encoding, and many variations are possible on the size <li>0xF0, next 65536 octets of data; and </li>
of the Partial Body Length headers, as long as a regular Body Length header enc <li>0xC5, 0xDD, last 1693 octets of data.</li>
odes the last portion of the data.</t> </ul>
<t>This is just one possible encoding, and many variations are possible on the s
<t>Please note that in all of these explanations, the total length of the packet ize of the Partial Body Length headers, as long as a regular Body Length header
is the length of the header(s) plus the length of the body.</t> encodes the last portion of the data.</t>
<t>Please note that in all of these explanations, the total length of
</section> the packet is the length of the header(s) plus the length of the body.</t>
</section> </section>
<section anchor="packet-criticality"><name>Packet Criticality</name> </section>
<section anchor="packet-criticality">
<t>The Packet Type ID space is partitioned into critical packets and non-critica <name>Packet Criticality</name>
l packets. <t>The Packet Type ID space is partitioned into critical packets and non
-critical packets.
If an implementation encounters a critical packet where the packet type is unkno wn in a packet sequence, it <bcp14>MUST</bcp14> reject the whole packet sequence (see <xref target="packet-sequence-composition"/>). If an implementation encounters a critical packet where the packet type is unkno wn in a packet sequence, it <bcp14>MUST</bcp14> reject the whole packet sequence (see <xref target="packet-sequence-composition"/>).
On the other hand, an unknown non-critical packet <bcp14>MUST</bcp14> be ignored .</t> On the other hand, an unknown non-critical packet <bcp14>MUST</bcp14> be ignored .</t>
<t>Packets with Type IDs from 0 to 39 are critical.
<t>Packets with Type IDs from 0 to 39 are critical.
Packets with Type IDs from 40 to 63 are non-critical.</t> Packets with Type IDs from 40 to 63 are non-critical.</t>
</section>
</section> </section>
</section> <section anchor="packet-types">
<section anchor="packet-types"><name>Packet Types</name> <name>Packet Types</name>
<t>The defined packet types are as follows:</t>
<t>The defined packet types are as follows:</t> <table anchor="packet-types-registry">
<name>OpenPGP Packet Types Registry</name>
<texttable title="OpenPGP Packet Types registry" anchor="packet-types-registry"> <thead>
<ttcol align='right'>ID</ttcol> <tr>
<ttcol align='left'>Critical</ttcol> <th align="right">ID</th>
<ttcol align='left'>Packet Type Description</ttcol> <th align="left">Critical</th>
<ttcol align='left'>Reference</ttcol> <th align="left">Packet Type Description</th>
<ttcol align='left'>Shorthand</ttcol> <th align="left">Shorthand</th>
<c>0</c> <th align="left">Reference</th>
<c>yes</c> </tr>
<c>Reserved - a packet <bcp14>MUST NOT</bcp14> have this packet type ID</c </thead>
> <tbody>
<c>&#160;</c> <tr>
<c>&#160;</c> <td align="right">0</td>
<c>1</c> <td align="left">Yes</td>
<c>yes</c> <td align="left">Reserved - this Packet Type ID <bcp14>MUST NOT</bcp
<c>Public-Key Encrypted Session Key Packet</c> 14> be used</td>
<c><xref target="pkesk"/></c> <td align="left"> </td>
<c>PKESK</c> <td align="left"></td>
<c>2</c> </tr>
<c>yes</c> <tr>
<c>Signature Packet</c> <td align="right">1</td>
<c><xref target="signature-packet"/></c> <td align="left">Yes</td>
<c>SIG</c> <td align="left">Public Key Encrypted Session Key Packet</td>
<c>3</c> <td align="left">PKESK</td>
<c>yes</c> <td align="left"><xref target="pkesk"/></td>
<c>Symmetric-Key Encrypted Session Key Packet</c> </tr>
<c><xref target="skesk"/></c> <tr>
<c>SKESK</c> <td align="right">2</td>
<c>4</c> <td align="left">Yes</td>
<c>yes</c> <td align="left">Signature Packet</td>
<c>One-Pass Signature Packet</c> <td align="left">SIG</td>
<c><xref target="one-pass-sig"/></c> <td align="left"><xref target="signature-packet"/></td>
<c>OPS</c> </tr>
<c>5</c> <tr>
<c>yes</c> <td align="right">3</td>
<c>Secret-Key Packet</c> <td align="left">Yes</td>
<c><xref target="seckey"/></c> <td align="left">Symmetric Key Encrypted Session Key Packet</td>
<c>SECKEY</c> <td align="left">SKESK</td>
<c>6</c> <td align="left"><xref target="skesk"/></td>
<c>yes</c> </tr>
<c>Public-Key Packet</c> <tr>
<c><xref target="pubkey"/></c> <td align="right">4</td>
<c>PUBKEY</c> <td align="left">Yes</td>
<c>7</c> <td align="left">One-Pass Signature Packet</td>
<c>yes</c> <td align="left">OPS</td>
<c>Secret-Subkey Packet</c> <td align="left"><xref target="one-pass-sig"/></td>
<c><xref target="secsubkey"/></c> </tr>
<c>SECSUBKEY</c> <tr>
<c>8</c> <td align="right">5</td>
<c>yes</c> <td align="left">Yes</td>
<c>Compressed Data Packet</c> <td align="left">Secret Key Packet</td>
<c><xref target="compressed-data"/></c> <td align="left">SECKEY</td>
<c>COMP</c> <td align="left"><xref target="seckey"/></td>
<c>9</c> </tr>
<c>yes</c> <tr>
<c>Symmetrically Encrypted Data Packet</c> <td align="right">6</td>
<c><xref target="sed"/></c> <td align="left">Yes</td>
<c>SED</c> <td align="left">Public Key Packet</td>
<c>10</c> <td align="left">PUBKEY</td>
<c>yes</c> <td align="left"><xref target="pubkey"/></td>
<c>Marker Packet</c> </tr>
<c><xref target="marker-packet"/></c> <tr>
<c>MARKER</c> <td align="right">7</td>
<c>11</c> <td align="left">Yes</td>
<c>yes</c> <td align="left">Secret Subkey Packet</td>
<c>Literal Data Packet</c> <td align="left">SECSUBKEY</td>
<c><xref target="lit"/></c> <td align="left"><xref target="secsubkey"/></td>
<c>LIT</c> </tr>
<c>12</c> <tr>
<c>yes</c> <td align="right">8</td>
<c>Trust Packet</c> <td align="left">Yes</td>
<c><xref target="trust"/></c> <td align="left">Compressed Data Packet</td>
<c>TRUST</c> <td align="left">COMP</td>
<c>13</c> <td align="left"><xref target="compressed-data"/></td>
<c>yes</c> </tr>
<c>User ID Packet</c> <tr>
<c><xref target="uid"/></c> <td align="right">9</td>
<c>UID</c> <td align="left">Yes</td>
<c>14</c> <td align="left">Symmetrically Encrypted Data Packet</td>
<c>yes</c> <td align="left">SED</td>
<c>Public-Subkey Packet</c> <td align="left"><xref target="sed"/></td>
<c><xref target="pubsubkey"/></c> </tr>
<c>PUBSUBKEY</c> <tr>
<c>17</c> <td align="right">10</td>
<c>yes</c> <td align="left">Yes</td>
<c>User Attribute Packet</c> <td align="left">Marker Packet</td>
<c><xref target="user-attribute-packet"/></c> <td align="left">MARKER</td>
<c>UAT</c> <td align="left"><xref target="marker-packet"/></td>
<c>18</c> </tr>
<c>yes</c> <tr>
<c>Symmetrically Encrypted and Integrity Protected Data Packet</c> <td align="right">11</td>
<c><xref target="seipd"/></c> <td align="left">Yes</td>
<c>SEIPD</c> <td align="left">Literal Data Packet</td>
<c>19</c> <td align="left">LIT</td>
<c>yes</c> <td align="left"><xref target="lit"/></td>
<c>Reserved (formerly Modification Detection Code Packet)</c> </tr>
<c>(see <xref target="version-one-seipd"/>)</c> <tr>
<c>&#160;</c> <td align="right">12</td>
<c>20</c> <td align="left">Yes</td>
<c>yes</c> <td align="left">Trust Packet</td>
<c>Reserved</c> <td align="left">TRUST</td>
<c>&#160;</c> <td align="left"><xref target="trust"/></td>
<c>&#160;</c> </tr>
<c>21</c> <tr>
<c>yes</c> <td align="right">13</td>
<c>Padding Packet</c> <td align="left">Yes</td>
<c><xref target="padding-packet"/></c> <td align="left">User ID Packet</td>
<c>PADDING</c> <td align="left">UID</td>
<c>22 to 39</c> <td align="left"><xref target="uid"/></td>
<c>yes</c> </tr>
<c>Unassigned Critical Packet</c> <tr>
<c>&#160;</c> <td align="right">14</td>
<c>&#160;</c> <td align="left">Yes</td>
<c>40 to 59</c> <td align="left">Public Subkey Packet</td>
<c>no</c> <td align="left">PUBSUBKEY</td>
<c>Unassigned Non-Critical Packet</c> <td align="left"><xref target="pubsubkey"/></td>
<c>&#160;</c> </tr>
<c>&#160;</c> <tr>
<c>60 to 63</c> <td align="right">17</td>
<c>no</c> <td align="left">Yes</td>
<c>Private or Experimental Values</c> <td align="left">User Attribute Packet</td>
<c>&#160;</c> <td align="left">UAT</td>
<c>&#160;</c> <td align="left"><xref target="user-attribute-packet"/></td>
</texttable> </tr>
<tr>
<t>The labels in the "Shorthand" column are used for compact reference elsewhere <td align="right">18</td>
in this draft, and may also be used by implementations that provide debugging o <td align="left">Yes</td>
r inspection affordances for streams of OpenPGP packets.</t> <td align="left">Symmetrically Encrypted and Integrity Protected Dat
a Packet</td>
<section anchor="pkesk"><name>Public-Key Encrypted Session Key Packet (Type ID 1 <td align="left">SEIPD</td>
)</name> <td align="left"><xref target="seipd"/></td>
</tr>
<t>Zero or more Public-Key Encrypted Session Key (PKESK) packets and/or Symmetri <tr>
c-Key Encrypted Session Key packets (<xref target="skesk"/>) precede an encrypti <td align="right">19</td>
on container (that is, a Symmetrically Encrypted Integrity Protected Data packet <td align="left">Yes</td>
or --- for historic data --- a Symmetrically Encrypted Data packet), which hold <td align="left">Reserved (formerly Modification Detection Code Pack
s an encrypted message. et)</td>
The message is encrypted with the session key, and the session key is itself enc <td align="left"> </td>
rypted and stored in the Encrypted Session Key packet(s). <td align="left"><xref target="version-one-seipd"/></td>
The encryption container is preceded by one Public-Key Encrypted Session Key pac </tr>
ket for each OpenPGP key to which the message is encrypted. <tr>
The recipient of the message finds a session key that is encrypted to their publ <td align="right">20</td>
ic key, decrypts the session key, and then uses the session key to decrypt the m <td align="left">Yes</td>
essage.</t> <td align="left">Reserved</td>
<td align="left"> </td>
<t>The body of this packet starts with a one-octet number giving the version num <td align="left"></td>
ber of the packet type. </tr>
The currently defined versions are 3 and 6. <tr>
The remainder of the packet depends on the version.</t> <td align="right">21</td>
<td align="left">Yes</td>
<t>The versions differ in how they identify the recipient key, and in what they <td align="left">Padding Packet</td>
encode. <td align="left">PADDING</td>
<td align="left"><xref target="padding-packet"/></td>
</tr>
<tr>
<td align="right">22-39</td>
<td align="left">Yes</td>
<td align="left">Unassigned Critical Packets</td>
<td align="left"> </td>
<td align="left"> </td>
</tr>
<tr>
<td align="right">40-59</td>
<td align="left">No</td>
<td align="left">Unassigned Non-Critical Packets</td>
<td align="left"> </td>
<td align="left"> </td>
</tr>
<tr>
<td align="right">60-63</td>
<td align="left">No</td>
<td align="left">Private or Experimental Use</td>
<td align="left"> </td>
<td align="left"></td>
</tr>
</tbody>
</table>
<t>The labels in the "Shorthand" column are used for compact reference els
ewhere in this document, and they may also be used by implementations that provi
de debugging or inspection affordances for streams of OpenPGP packets.</t>
<section anchor="pkesk">
<name>Public Key Encrypted Session Key Packet (Type ID 1)</name>
<t>Zero or more PKESK packets and/or SKESK packets (<xref target="skesk"
/>) precede an encryption container (that is, a Symmetrically Encrypted and Inte
grity Protected Data (SEIPD) packet or -- for historic data -- a Symmetrically E
ncrypted Data (SED) packet), which holds an Encrypted Message.
The message is encrypted with the session key, and the session key is itself enc
rypted and stored in the Encrypted Session Key packet(s). The encryption contain
er is preceded by one Public Key Encrypted Session Key packet for each OpenPGP K
ey to which the message is encrypted. The recipient of the message finds a sessi
on key that is encrypted to their public key, decrypts the session key, and then
uses the session key to decrypt the message.</t>
<t>The body of this packet starts with a 1-octet number giving the versi
on number of the packet type. The currently defined versions are 3 and 6. The re
mainder of the packet depends on the version.</t>
<t>The versions differ in how they identify the recipient key and in wha
t they encode.
The version of the PKESK packet must align with the version of the SEIPD packet (see <xref target="encrypted-message-versions"/>). The version of the PKESK packet must align with the version of the SEIPD packet (see <xref target="encrypted-message-versions"/>).
Any new version of the PKESK packet should be registered in the registry establi shed in <xref target="encrypted-message-versions"/>.</t> Any new version of the PKESK packet should be registered in the registry establi shed in <xref target="encrypted-message-versions"/>.</t>
<section anchor="v3-pkesk">
<section anchor="v3-pkesk"><name>Version 3 Public-Key Encrypted Session Key Pack <name>Version 3 Public Key Encrypted Session Key Packet Format</name>
et Format</name> <t>A version 3 PKESK packet precedes a v1 SEIPD packet (see <xref targ
et="version-one-seipd"/>).
<t>A version 3 Public-Key Encrypted Session Key (PKESK) packet precedes a versio In historic data, it is sometimes found preceding a deprecated SED packet; see <
n 1 Symmetrically Encrypted Integrity Protected Data (v1 SEIPD, see <xref target xref target="sed"/>.
="version-one-seipd"/>) packet.
In historic data, it is sometimes found preceding a deprecated Symmetrically Enc
rypted Data packet (SED, see <xref target="sed"/>).
A v3 PKESK packet <bcp14>MUST NOT</bcp14> precede a v2 SEIPD packet (see <xref t arget="encrypted-message-versions"/>).</t> A v3 PKESK packet <bcp14>MUST NOT</bcp14> precede a v2 SEIPD packet (see <xref t arget="encrypted-message-versions"/>).</t>
<t>The v3 PKESK packet consists of:</t>
<t>The v3 PKESK packet consists of:</t> <ul spacing="normal">
<li>A 1-octet version number with value 3.
<t><list style="symbols"> </li>
<t>A one-octet version number with value 3.</t> <li>An 8-octet number that gives the Key ID of the public key to whi
<t>An eight-octet number that gives the Key ID of the public key to which the ch the session key is encrypted.
session key is encrypted.
If the session key is encrypted to a subkey, then the Key ID of this subkey is u sed here instead of the Key ID of the primary key. If the session key is encrypted to a subkey, then the Key ID of this subkey is u sed here instead of the Key ID of the primary key.
The Key ID may also be all zeros, for an "anonymous recipient" (see <xref target The Key ID may also be all zeros, for an "anonymous recipient" (see <xref target
="pkesk-notes"/>).</t> ="pkesk-notes"/>).
<t>A one-octet number giving the public-key algorithm used.</t> </li>
<t>A series of values comprising the encrypted session key. <li>A 1-octet number giving the public key algorithm used.
This is algorithm-specific and described below.</t> </li>
</list></t> <li>A series of values comprising the encrypted session key.
This is algorithm specific and described below.
<t>The public-key encryption algorithm (described in subsequent sections) is pas </li>
sed two values:</t> </ul>
<t>The public key encryption algorithm (described in subsequent sectio
<t><list style="symbols"> ns) is passed two values:</t>
<t>The session key.</t> <ul spacing="normal">
<t>The one-octet algorithm identifier that specifies the symmetric encryption <li>The session key.
algorithm used to encrypt the following v1 SEIPD packet.</t> </li>
</list></t> <li>
<t>The 1-octet algorithm identifier that specifies the symmetric k
</section> ey encryption algorithm used to encrypt the v1 SEIPD packet described in the fol
<section anchor="v6-pkesk"><name>Version 6 Public-Key Encrypted Session Key Pack lowing section.</t>
et Format</name> </li>
</ul>
<t>A version 6 Public-Key Encrypted Session Key (PKESK) packet precedes a versio </section>
n 2 Symmetrically Encrypted Integrity Protected Data (v2 SEIPD, see <xref target <section anchor="v6-pkesk">
="version-two-seipd"/>) packet. <name>Version 6 Public Key Encrypted Session Key Packet Format</name>
A v6 PKESK packet <bcp14>MUST NOT</bcp14> precede a v1 SEIPD packet or a depreca <t>A v6 PKESK packet precedes a v2 SEIPD packet (see <xref target="ver
ted Symmetrically Encrypted Data packet (see <xref target="encrypted-message-ver sion-two-seipd"/>).
sions"/>).</t> A v6 PKESK packet <bcp14>MUST NOT</bcp14> precede a v1 SEIPD packet or a depreca
ted SED packet (see <xref target="encrypted-message-versions"/>).</t>
<t>The v6 PKESK packet consists of the following fields:</t> <t>The v6 PKESK packet consists of the following fields:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>A 1-octet version number with value 6.
<t>A one-octet version number with value 6.</t> </li>
<t>A one-octet size of the following two fields. <li>A 1-octet size of the following two fields.
This size may be zero, if the key version number field and the fingerprint field This size may be zero, if the key version number field and the fingerprint field
are omitted for an "anonymous recipient" (see <xref target="pkesk-notes"/>).</t are omitted for an "anonymous recipient" (see <xref target="pkesk-notes"/>).
> </li>
<t>A one octet key version number.</t> <li>A 1-octet key version number.
<t>The fingerprint of the public key or subkey to which the session key is enc </li>
rypted. <li>The fingerprint of the public key or subkey to which the session
Note that the length N of the fingerprint for a version 4 key is 20 octets; for key is encrypted.
a version 6 key N is 32.</t> Note that the length N of the fingerprint for a version 4 key is 20 octets; for
<t>A one-octet number giving the public-key algorithm used.</t> a version 6 key, N is 32.
<t>A series of values comprising the encrypted session key. </li>
This is algorithm-specific and described below.</t> <li>A 1-octet number giving the public key algorithm used.
</list></t> </li>
<li>A series of values comprising the encrypted session key.
<t>The session key is encrypted according to the public-key algorithm used, as d This is algorithm specific and described below.
escribed below. </li>
No symmetric encryption algorithm identifier is passed to the public-key algorit </ul>
hm for a v6 PKESK packet, as it is included in the v2 SEIPD packet.</t> <t>The session key is encrypted according to the public key algorithm
used, as described below.
</section> No symmetric key encryption algorithm identifier is passed to the public key alg
<section anchor="pkesk-rsa"><name>Algorithm-Specific Fields for RSA encryption</ orithm for a v6 PKESK packet, as it is included in the v2 SEIPD packet.</t>
name> </section>
<section anchor="pkesk-rsa">
<t><list style="symbols"> <name>Algorithm-Specific Fields for RSA Encryption</name>
<t>Multiprecision integer (MPI) of RSA-encrypted value m**e mod n.</t> <ul spacing="normal">
</list></t> <li>MPI of RSA-encrypted value m<sup>e</sup> mod n.
</li>
<t>To produce the value "m" in the above formula, first concatenate the followin </ul>
g values:</t> <t>To produce the value "m" in the above formula, first concatenate th
e following values:</t>
<t><list style="symbols"> <ul spacing="normal">
<t>The one-octet algorithm identifier, if it was passed (in the case of a v3 P <li>The 1-octet algorithm identifier, if it was passed (in the case
KESK packet).</t> of a v3 PKESK packet).
<t>The session key.</t> </li>
<t>A two-octet checksum of the session key, equal to the sum of the session ke <li>The session key.
y octets, modulo 65536.</t> </li>
</list></t> <li>A 2-octet checksum of the session key, equal to the sum of the s
ession key octets, modulo 65536.
<t>Then, the above values are encoded using the PKCS#1 block encoding EME-PKCS1- </li>
v1_5 described in step 2 of <xref section="7.2.1" sectionFormat="of" target="RFC </ul>
8017"/> (see also <xref target="eme-pkcs1-v1-5-encode"/>). <t>Then, the above values are encoded using the PKCS#1 block encoding
When decoding "m" during decryption, an implementation should follow step 3 of < EME-PKCS1-v1_5, as described in Step 2 in <xref section="7.2.1" sectionFormat="o
xref section="7.2.2" sectionFormat="of" target="RFC8017"/> (see also <xref targe f" target="RFC8017"/> (see also <xref target="eme-pkcs1-v1-5-encode"/>).
t="eme-pkcs1-v1-5-decode"/>).</t> When decoding "m" during decryption, an implementation should follow St
ep 3 in <xref section="7.2.2" sectionFormat="of" target="RFC8017"/> (see also <x
<t>Note that when an implementation forms several PKESKs with one session key, f ref target="eme-pkcs1-v1-5-decode"/>).</t>
orming a message that can be decrypted by several keys, the implementation <bcp1 <t>Note that when an implementation forms several PKESK packets with o
4>MUST</bcp14> make a new PKCS#1 encoding for each key. ne session key, forming a message that can be decrypted by several keys, the imp
This defends against attacks such as those discussed in <xref target="HASTAD"/>. lementation <bcp14>MUST</bcp14> make a new PKCS#1 encoding for each key. This de
</t> fends against attacks such as those discussed in <xref target="HASTAD"/>.</t>
</section>
</section> <section anchor="pkesk-elgamal">
<section anchor="pkesk-elgamal"><name>Algorithm-Specific Fields for Elgamal encr <name>Algorithm-Specific Fields for Elgamal Encryption</name>
yption</name> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>MPI of Elgamal (Diffie-Hellman) value g<sup>k</sup> mod p.</t>
<t>MPI of Elgamal (Diffie-Hellman) value g**k mod p.</t> </li>
<t>MPI of Elgamal (Diffie-Hellman) value m * y**k mod p.</t> <li>
</list></t> <t>MPI of Elgamal (Diffie-Hellman) value m * y<sup>k</sup> mod p.<
/t>
<t>To produce the value "m" in the above formula, first concatenate the followin </li>
g values:</t> </ul>
<t>To produce the value "m" in the above formula, first concatenate th
<t><list style="symbols"> e following values:</t>
<t>The one-octet algorithm identifier, if it was passed (in the case of a v3 P <ul spacing="normal">
KESK packet).</t> <li>
<t>The session key.</t> <t>The 1-octet algorithm identifier, if it was passed (in the case
<t>A two-octet checksum of the session key, equal to the sum of the session ke of a v3 PKESK packet).</t>
y octets, modulo 65536.</t> </li>
</list></t> <li>
<t>The session key.</t>
<t>Then, the above values are encoded using the PKCS#1 block encoding EME-PKCS1- </li>
v1_5 described in step 2 of <xref section="7.2.1" sectionFormat="of" target="RFC <li>
8017"/> (see also <xref target="eme-pkcs1-v1-5-encode"/>). <t>A 2-octet checksum of the session key, equal to the sum of the
When decoding "m" during decryption, an implementation should follow step 3 of < session key octets, modulo 65536.</t>
xref section="7.2.2" sectionFormat="of" target="RFC8017"/> (see also <xref targe </li>
t="eme-pkcs1-v1-5-decode"/>).</t> </ul>
<t>Then, the above values are encoded using the PKCS#1 block encoding
<t>Note that when an implementation forms several PKESKs with one session key, f EME-PKCS1-v1_5, as described in Step 2 in <xref section="7.2.1" sectionFormat="o
orming a message that can be decrypted by several keys, the implementation <bcp1 f" target="RFC8017"/> (see also <xref target="eme-pkcs1-v1-5-encode"/>).
4>MUST</bcp14> make a new PKCS#1 encoding for each key. When decoding "m" during decryption, an implementation should follow Step 3 in <
xref section="7.2.2" sectionFormat="of" target="RFC8017"/> (see also <xref targe
t="eme-pkcs1-v1-5-decode"/>).</t>
<t>Note that when an implementation forms several PKESK packets with o
ne session key, forming a message that can be decrypted by several keys, the imp
lementation <bcp14>MUST</bcp14> make a new PKCS#1 encoding for each key.
This defends against attacks such as those discussed in <xref target="HASTAD"/>. </t> This defends against attacks such as those discussed in <xref target="HASTAD"/>. </t>
<t>An implementation <bcp14>MUST NOT</bcp14> generate ElGamal v6 PKESK
packets.</t>
</section>
<section anchor="pkesk-ecdh">
<name>Algorithm-Specific Fields for ECDH Encryption</name>
<ul spacing="normal">
<li>MPI of an EC point representing an ephemeral public key in the p
oint format associated with the curve as specified in <xref target="ec-curves"/>
.
</li>
<li>A 1-octet size, followed by a symmetric key encoded using the me
thod described in <xref target="ecdh"/>.
</li>
</ul>
</section>
<section anchor="pkesk-x25519">
<name>Algorithm-Specific Fields for X25519 Encryption</name>
<t>An implementation <bcp14>MUST NOT</bcp14> generate ElGamal v6 PKESKs.</t> <ul spacing="normal">
<li>32 octets representing an ephemeral X25519 public key.
</section> </li>
<section anchor="pkesk-ecdh"><name>Algorithm-Specific Fields for ECDH encryption <li>A 1-octet size of the following fields.
</name> </li>
<li>The 1-octet algorithm identifier, if it was passed (in the case
<t><list style="symbols"> of a v3 PKESK packet).
<t>MPI of an EC point representing an ephemeral public key, in the point forma </li>
t associated with the curve as specified in <xref target="ec-curves"/>.</t> <li>The encrypted session key.
<t>A one-octet size, followed by a symmetric key encoded using the method desc </li>
ribed in <xref target="ecdh"/>.</t> </ul>
</list></t> <t>See <xref section="6.1" sectionFormat="of" target="RFC7748"/> for m
ore details on the computation of the ephemeral public key and the shared secret
</section> . The HMAC-based Key Derivation Function (HKDF) <xref target="RFC5869"/> is then
<section anchor="pkesk-x25519"><name>Algorithm-Specific Fields for X25519 encryp used with SHA256 <xref target="RFC6234"/> and an info parameter of "OpenPGP X25
tion</name> 519" and no salt.
<t><list style="symbols">
<t>32 octets representing an ephemeral X25519 public key.</t>
<t>A one-octet size of the following fields.</t>
<t>The one-octet algorithm identifier, if it was passed (in the case of a v3 P
KESK packet).</t>
<t>The encrypted session key.</t>
</list></t>
<t>See <xref section="6.1" sectionFormat="of" target="RFC7748"/> for more detail
s on the computation of the ephemeral public key and the shared secret.
HKDF (<xref target="RFC5869"/>) is then used with SHA256 <xref target="RFC6234"/
> and an info parameter of "OpenPGP X25519" and no salt.
The input of HKDF is the concatenation of the following three values:</t>
<t><list style="symbols">
<t>32 octets of the ephemeral X25519 public key from this packet.</t>
<t>32 octets of the recipient public key material.</t>
<t>32 octets of the shared secret.</t>
</list></t>
<t>The key produced from HKDF is used to encrypt the session key with AES-128 ke
y wrap, as defined in <xref target="RFC3394"/>.</t>
<t>Note that unlike ECDH, no checksum or padding are appended to the session key
before key wrapping.
Finally, note that unlike the other public-key algorithms, in the case of a v3 P
KESK packet, the symmetric algorithm ID is not encrypted.
Instead, it is prepended to the encrypted session key in plaintext.
In this case, the symmetric algorithm used <bcp14>MUST</bcp14> be AES-128, AES-1
92 or AES-256 (algorithm ID 7, 8 or 9).</t>
</section>
<section anchor="pkesk-x448"><name>Algorithm-Specific Fields for X448 encryption
</name>
<t><list style="symbols">
<t>56 octets representing an ephemeral X448 public key.</t>
<t>A one-octet size of the following fields.</t>
<t>The one-octet algorithm identifier, if it was passed (in the case of a v3 P
KESK packet).</t>
<t>The encrypted session key.</t>
</list></t>
<t>See <xref section="6.2" sectionFormat="of" target="RFC7748"/> for more detail
s on the computation of the ephemeral public key and the shared secret.
HKDF (<xref target="RFC5869"/>) is then used with SHA512 (<xref target="RFC6234"
/>) and an info parameter of "OpenPGP X448" and no salt.
The input of HKDF is the concatenation of the following three values:</t> The input of HKDF is the concatenation of the following three values:</t>
<ul spacing="normal">
<li>
<t>32 octets of the ephemeral X25519 public key from this packet.<
/t>
</li>
<li>
<t>32 octets of the recipient public key material.</t>
</li>
<li>
<t>32 octets of the shared secret.</t>
</li>
</ul>
<t>The key produced from HKDF is used to encrypt the session key with
AES-128 key wrap, as defined in <xref target="RFC3394"/>.</t>
<t><list style="symbols"> <t>Note that unlike Elliptic Curve Diffie-Hellman (ECDH), no checksum
<t>56 octets of the ephemeral X448 public key from this packet.</t> or padding are appended to the session key before key wrapping. Finally, note th
<t>56 octets of the recipient public key material.</t> at unlike the other public key algorithms, in the case of a v3 PKESK packet, the
<t>56 octets of the shared secret.</t> symmetric algorithm ID is not encrypted. Instead, it is prepended to the encryp
</list></t> ted session key in plaintext.
In this case, the symmetric algorithm used <bcp14>MUST</bcp14> be AES-128, AES-1
<t>The key produced from HKDF is used to encrypt the session key with AES-256 ke 92, or AES-256 (algorithm IDs 7, 8, or 9, respectively).</t>
y wrap, as defined in <xref target="RFC3394"/>.</t> </section>
<section anchor="pkesk-x448">
<t>Note that unlike ECDH, no checksum or padding are appended to the session key <name>Algorithm-Specific Fields for X448 Encryption</name>
before key wrapping. <ul spacing="normal">
Finally, note that unlike the other public-key algorithms, in the case of a v3 P <li>
KESK packet, the symmetric algorithm ID is not encrypted. <t>56 octets representing an ephemeral X448 public key.</t>
</li>
<li>
<t>A 1-octet size of the following fields.</t>
</li>
<li>
<t>The 1-octet algorithm identifier, if it was passed (in the case
of a v3 PKESK packet).</t>
</li>
<li>
<t>The encrypted session key.</t>
</li>
</ul>
<t>See <xref section="6.2" sectionFormat="of" target="RFC7748"/> for m
ore details on the computation of the ephemeral public key and the shared secret
.
HKDF <xref target="RFC5869"/> is then used with SHA512 <xref target="RFC6234"/>
and an info parameter of "OpenPGP X448" and no salt. The input of HKDF is the co
ncatenation of the following three values:</t>
<ul spacing="normal">
<li>
<t>56 octets of the ephemeral X448 public key from this packet.</t
>
</li>
<li>
<t>56 octets of the recipient public key material.</t>
</li>
<li>
<t>56 octets of the shared secret.</t>
</li>
</ul>
<t>The key produced from HKDF is used to encrypt the session key with
AES-256 key wrap, as defined in <xref target="RFC3394"/>.</t>
<t>Note that unlike ECDH, no checksum or padding are appended to the s
ession key before key wrapping.
Finally, note that unlike the other public key algorithms, in the case of a v3 P
KESK packet, the symmetric algorithm ID is not encrypted.
Instead, it is prepended to the encrypted session key in plaintext. Instead, it is prepended to the encrypted session key in plaintext.
In this case, the symmetric algorithm used <bcp14>MUST</bcp14> be AES-128, AES-1 In this case, the symmetric algorithm used <bcp14>MUST</bcp14> be AES-128, AES-1
92 or AES-256 (algorithm ID 7, 8 or 9).</t> 92, or AES-256 (algorithm ID 7, 8, or 9).</t>
</section>
</section> <section anchor="pkesk-notes">
<section anchor="pkesk-notes"><name>Notes on PKESK</name> <name>Notes on PKESK</name>
<t>An implementation <bcp14>MAY</bcp14> accept or use a Key ID of all
<t>An implementation <bcp14>MAY</bcp14> accept or use a Key ID of all zeros, or zeros, or an omitted key fingerprint, to hide the intended decryption key.
an omitted key fingerprint, to hide the intended decryption key.
In this case, the receiving implementation would try all available private keys, checking for a valid decrypted session key. In this case, the receiving implementation would try all available private keys, checking for a valid decrypted session key.
This format helps reduce traffic analysis of messages.</t> This format helps reduce traffic analysis of messages.</t>
</section>
</section> </section>
</section> <section anchor="signature-packet">
<section anchor="signature-packet"><name>Signature Packet (Type ID 2)</name> <name>Signature Packet (Type ID 2)</name>
<t>A Signature packet describes a binding between some public key and so
<t>A Signature packet describes a binding between some public key and some data. me data.
The most common signatures are a signature of a file or a block of text, and a s The most common signatures are a signature of a file or a block of text and a si
ignature that is a certification of a User ID.</t> gnature that is a certification of a User ID.</t>
<t>Three versions of Signature packets are defined.
<t>Three versions of Signature packets are defined.
Version 3 provides basic signature information, while versions 4 and 6 provide a n expandable format with subpackets that can specify more information about the signature.</t> Version 3 provides basic signature information, while versions 4 and 6 provide a n expandable format with subpackets that can specify more information about the signature.</t>
<t>For historical reasons, versions 1, 2, and 5 of the Signature packet
<t>For historical reasons, versions 1, 2, and 5 of the Signature packet are unsp are unspecified.
ecified.
Any new Signature packet version should be registered in the registry establishe d in <xref target="signed-message-versions"/>.</t> Any new Signature packet version should be registered in the registry establishe d in <xref target="signed-message-versions"/>.</t>
<t>An implementation <bcp14>MUST</bcp14> generate a version 6 signature
<t>An implementation <bcp14>MUST</bcp14> generate a version 6 signature when sig when signing with a version 6 key.
ning with a version 6 key.
An implementation <bcp14>MUST</bcp14> generate a version 4 signature when signin g with a version 4 key. An implementation <bcp14>MUST</bcp14> generate a version 4 signature when signin g with a version 4 key.
Implementations <bcp14>MUST NOT</bcp14> create version 3 signatures; they <bcp14 >MAY</bcp14> accept version 3 signatures. Implementations <bcp14>MUST NOT</bcp14> create version 3 signatures; they <bcp14 >MAY</bcp14> accept version 3 signatures.
See <xref target="signed-message-versions"/> for more details about packet versi on correspondence between keys and signatures.</t> See <xref target="signed-message-versions"/> for more details about packet versi on correspondence between keys and signatures.</t>
<section anchor="signature-types">
<section anchor="signature-types"><name>Signature Types</name> <name>Signature Types</name>
<t>There are a number of possible meanings for a signature, which are
<t>There are a number of possible meanings for a signature, which are indicated indicated by the Signature Type ID in any given signature. Please note that the
by the signature type ID in any given signature. vagueness of these meanings is not a flaw but rather a feature of the system.
Please note that the vagueness of these meanings is not a flaw, but a feature of
the system.
Because OpenPGP places final authority for validity upon the receiver of a signa ture, it may be that one signer's casual act might be more rigorous than some ot her authority's positive act. Because OpenPGP places final authority for validity upon the receiver of a signa ture, it may be that one signer's casual act might be more rigorous than some ot her authority's positive act.
See <xref target="computing-signatures"/> for detailed information on how to com pute and verify signatures of each type.</t> See <xref target="computing-signatures"/> for detailed information on how to com pute and verify signatures of each type.</t>
<table anchor="signature-types-registry">
<name>OpenPGP Signature Types Registry</name>
<thead>
<tr>
<th align="left">ID</th>
<th align="left">Name</th>
<th align="left">Reference</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">0x00</td>
<td align="left">Binary Signature</td>
<td align="left">
<xref target="sigtype-binary"/></td>
</tr>
<tr>
<td align="left">0x01</td>
<td align="left">Text Signature</td>
<td align="left">
<xref target="sigtype-text"/></td>
</tr>
<tr>
<td align="left">0x02</td>
<td align="left">Standalone Signature</td>
<td align="left">
<xref target="sigtype-standalone"/></td>
</tr>
<tr>
<td align="left">0x10</td>
<td align="left">Generic Certification Signature</td>
<td align="left">
<xref target="sigtype-generic-cert"/></td>
</tr>
<tr>
<td align="left">0x11</td>
<td align="left">Persona Certification Signature</td>
<td align="left">
<xref target="sigtype-persona-cert"/></td>
</tr>
<tr>
<td align="left">0x12</td>
<td align="left">Casual Certification Signature</td>
<td align="left">
<xref target="sigtype-casual-cert"/></td>
</tr>
<tr>
<td align="left">0x13</td>
<td align="left">Positive Certification Signature</td>
<td align="left">
<xref target="sigtype-positive-cert"/></td>
</tr>
<tr>
<td align="left">0x18</td>
<td align="left">Subkey Binding Signature</td>
<td align="left">
<xref target="sigtype-subkey-binding"/></td>
</tr>
<tr>
<td align="left">0x19</td>
<td align="left">Primary Key Binding Signature</td>
<td align="left">
<xref target="sigtype-primary-binding"/></td>
</tr>
<tr>
<td align="left">0x1F</td>
<td align="left">Direct Key Signature</td>
<td align="left">
<xref target="sigtype-direct-key"/></td>
</tr>
<tr>
<td align="left">0x20</td>
<td align="left">Key Revocation Signature</td>
<td align="left">
<xref target="sigtype-key-revocation"/></td>
</tr>
<tr>
<td align="left">0x28</td>
<td align="left">Subkey Revocation Signature</td>
<td align="left">
<xref target="sigtype-subkey-revocation"/></td>
</tr>
<tr>
<td align="left">0x30</td>
<td align="left">Certification Revocation Signature</td>
<td align="left">
<xref target="sigtype-certification-revocation"/></td>
</tr>
<tr>
<td align="left">0x40</td>
<td align="left">Timestamp Signature</td>
<td align="left">
<xref target="sigtype-timestamp"/></td>
</tr>
<tr>
<td align="left">0x50</td>
<td align="left">Third-Party Confirmation Signature</td>
<td align="left">
<xref target="sigtype-third-party-confirmation"/></td>
</tr>
<tr>
<td align="left">0xFF</td>
<td align="left">Reserved</td>
<td align="left"><xref target="sigtype-reserved"/>
</td>
</tr>
</tbody>
</table>
<t>The meanings of each signature type are described in the subsection
s below.</t>
<texttable title="OpenPGP Signature Types registry" anchor="signature-types-regi <section anchor="sigtype-binary">
stry"> <name>Binary Signature (Type ID 0x00) of a Document</name>
<ttcol align='left'>ID</ttcol> <t>This means the signer owns it, created it, or certifies that it h
<ttcol align='left'>Name</ttcol> as not been modified.</t>
<ttcol align='left'>Reference</ttcol> </section>
<c>0x00</c> <section anchor="sigtype-text">
<c>Binary Signature</c> <name>Text Signature (Type ID 0x01) of a Canonical Document</name>
<c><xref target="sigtype-binary"/></c> <t>This means the signer owns it, created it, or certifies that it h
<c>0x01</c> as not been modified.
<c>Text Signature</c>
<c><xref target="sigtype-text"/></c>
<c>0x02</c>
<c>Standalone Signature</c>
<c><xref target="sigtype-standalone"/></c>
<c>0x10</c>
<c>Generic Certification</c>
<c><xref target="sigtype-generic-cert"/></c>
<c>0x11</c>
<c>Persona Certification</c>
<c><xref target="sigtype-persona-cert"/></c>
<c>0x12</c>
<c>Casual Certification</c>
<c><xref target="sigtype-casual-cert"/></c>
<c>0x13</c>
<c>Positive Certification</c>
<c><xref target="sigtype-positive-cert"/></c>
<c>0x18</c>
<c>Subkey Binding Signature</c>
<c><xref target="sigtype-subkey-binding"/></c>
<c>0x19</c>
<c>Primary Key Binding Signature</c>
<c><xref target="sigtype-primary-binding"/></c>
<c>0x1F</c>
<c>Direct Key Signature</c>
<c><xref target="sigtype-direct-key"/></c>
<c>0x20</c>
<c>Key Revocation</c>
<c><xref target="sigtype-key-revocation"/></c>
<c>0x28</c>
<c>Subkey Revocation</c>
<c><xref target="sigtype-subkey-revocation"/></c>
<c>0x30</c>
<c>Certification Revocation</c>
<c><xref target="sigtype-certification-revocation"/></c>
<c>0x40</c>
<c>Timestamp Signature</c>
<c><xref target="sigtype-timestamp"/></c>
<c>0x50</c>
<c>Third-Party Confirmation</c>
<c><xref target="sigtype-third-party-confirmation"/></c>
<c>0xFF</c>
<c>Reserved</c>
<c><xref target="sigtype-reserved"/></c>
</texttable>
<t>These meanings of each signature type are described in the subsections below.
</t>
<section anchor="sigtype-binary"><name>Signature of a binary document (type ID 0
x00)</name>
<t>This means the signer owns it, created it, or certifies that it has not been
modified.</t>
</section>
<section anchor="sigtype-text"><name>Signature of a canonical text document (typ
e ID 0x01)</name>
<t>This means the signer owns it, created it, or certifies that it has not been
modified.
The signature is calculated over the text data with its line endings converted t o &lt;CR&gt;&lt;LF&gt;.</t> The signature is calculated over the text data with its line endings converted t o &lt;CR&gt;&lt;LF&gt;.</t>
</section>
</section> <section anchor="sigtype-standalone">
<section anchor="sigtype-standalone"><name>Standalone signature (type ID 0x02)</ <name>Standalone Signature (Type ID 0x02)</name>
name> <t>This signature is a signature of only its own subpacket contents.
<t>This signature is a signature of only its own subpacket contents.
It is calculated identically to a signature over a zero-length binary document. It is calculated identically to a signature over a zero-length binary document.
V3 standalone signatures <bcp14>MUST NOT</bcp14> be generated and <bcp14>MUST</ Version 3 Standalone signatures <bcp14>MUST NOT</bcp14> be generated and <bcp14
bcp14> be ignored.</t> >MUST</bcp14> be ignored.</t>
</section>
</section> <section anchor="sigtype-generic-cert">
<section anchor="sigtype-generic-cert"><name>Generic certification of a User ID <name>Generic Certification Signature (Type ID 0x10) of a User ID an
and Public-Key packet (type ID 0x10)</name> d Public Key Packet</name>
<t>The issuer of this certification does not make any particular ass
<t>The issuer of this certification does not make any particular assertion as to ertion as to how well the certifier has checked that the owner of the key is in
how well the certifier has checked that the owner of the key is in fact the per fact the person described by the User ID.</t>
son described by the User ID.</t> </section>
<section anchor="sigtype-persona-cert">
</section> <name>Persona Certification Signature (Type ID 0x11) of a User ID an
<section anchor="sigtype-persona-cert"><name>Persona certification of a User ID d Public Key Packet</name>
and Public-Key packet (type ID 0x11)</name> <t>The issuer of this certification has not done any verification of
the claim that the owner of this key is the User ID specified.</t>
<t>The issuer of this certification has not done any verification of the claim t </section>
hat the owner of this key is the User ID specified.</t> <section anchor="sigtype-casual-cert">
<name>Casual Certification Signature (Type ID 0x12) of a User ID and
</section> Public Key Packet</name>
<section anchor="sigtype-casual-cert"><name>Casual certification of a User ID an <t>The issuer of this certification has done some casual verificatio
d Public-Key packet (type ID 0x12)</name> n of the claim of identity.</t>
</section>
<t>The issuer of this certification has done some casual verification of the cla <section anchor="sigtype-positive-cert">
im of identity.</t> <name>Positive Certification Signature (Type ID 0x13) of a User ID a
nd Public Key Packet</name>
</section> <t>The issuer of this certification has done substantial verificatio
<section anchor="sigtype-positive-cert"><name>Positive certification of a User I n of the claim of identity.</t>
D and Public-Key packet (type ID 0x13)</name> <t>Most OpenPGP implementations make their "key signatures" as gener
ic (Type ID 0x10) certifications. Some implementations can issue 0x11-0x13 certi
<t>The issuer of this certification has done substantial verification of the cla fications, but few differentiate between the types.</t>
im of identity.</t> </section>
<section anchor="sigtype-subkey-binding">
<t>Most OpenPGP implementations make their "key signatures" as generic (type ID <name>Subkey Binding Signature (Type ID 0x18)</name>
0x10) certifications. <t>This signature is a statement by the top-level signing key, indic
Some implementations can issue 0x11-0x13 certifications, but few differentiate b ating that it owns the subkey. This signature is calculated directly on the prim
etween the types.</t> ary key and subkey, and not on any User ID or other packets. A signature that bi
nds a signing subkey <bcp14>MUST</bcp14> have an Embedded Signature subpacket in
</section> this binding signature that contains a 0x19 signature made by the signing subke
<section anchor="sigtype-subkey-binding"><name>Subkey Binding Signature (type ID y on the primary key and subkey.</t>
0x18)</name> </section>
<section anchor="sigtype-primary-binding">
<t>This signature is a statement by the top-level signing key that indicates tha <name>Primary Key Binding Signature (Type ID 0x19)</name>
t it owns the subkey. <t>This signature is a statement by a signing subkey, indicating tha
This signature is calculated directly on the primary key and subkey, and not on t it is owned by the primary key.
any User ID or other packets. This signature is calculated the same way as a Subkey Binding signature (Type ID
A signature that binds a signing subkey <bcp14>MUST</bcp14> have an Embedded Sig 0x18): directly on the primary key and subkey, and not on any User ID or other
nature subpacket in this binding signature that contains a 0x19 signature made b packets.</t>
y the signing subkey on the primary key and subkey.</t> </section>
<section anchor="sigtype-direct-key">
</section> <name>Direct Key Signature (Type ID 0x1F)</name>
<section anchor="sigtype-primary-binding"><name>Primary Key Binding Signature (t <t>This signature is calculated directly on a key.
ype ID 0x19)</name> It binds the information in the Signature subpackets to the key and is appropria
te to be used for subpackets that provide information about the key, such as the
<t>This signature is a statement by a signing subkey, indicating that it is owne Key Flags subpacket or the (deprecated) Revocation Key subpacket.
d by the primary key. It is also appropriate for statements that non-self certifiers want to make abou
This signature is calculated the same way as a subkey binding signature (0x18): t the key itself rather than the binding between a key and a name.</t>
directly on the primary key and subkey, and not on any User ID or other packets. </section>
</t> <section anchor="sigtype-key-revocation">
<name>Key Revocation Signature (Type ID 0x20)</name>
</section> <t>This signature is calculated directly on the key being revoked.
<section anchor="sigtype-direct-key"><name>Direct Key Signature (type ID 0x1F)</ A revoked key is not to be used. Only Revocation Signatures by the key being rev
name> oked, or by a (deprecated) Revocation Key, should be considered valid Revocation
Signatures.</t>
<t>This signature is calculated directly on a key. </section>
It binds the information in the Signature subpackets to the key, and is appropri <section anchor="sigtype-subkey-revocation">
ate to be used for subpackets that provide information about the key, such as th <name>Subkey Revocation Signature (Type ID 0x28)</name>
e Key Flags subpacket or (deprecated) Revocation Key. <t>This signature is calculated directly on the primary key and the
It is also appropriate for statements that non-self certifiers want to make abou subkey being revoked.
t the key itself, rather than the binding between a key and a name.</t>
</section>
<section anchor="sigtype-key-revocation"><name>Key revocation signature (type ID
0x20)</name>
<t>The signature is calculated directly on the key being revoked.
A revoked key is not to be used.
Only revocation signatures by the key being revoked, or by a (deprecated) Revoca
tion Key, should be considered valid revocation signatures.</t>
</section>
<section anchor="sigtype-subkey-revocation"><name>Subkey revocation signature (t
ype ID 0x28)</name>
<t>The signature is calculated directly on the primary key and the subkey being
revoked.
A revoked subkey is not to be used. A revoked subkey is not to be used.
Only revocation signatures by the top-level signature key that is bound to this Only Revocation Signatures by the top-level signature key that is bound to this
subkey, or by a (deprecated) Revocation Key, should be considered valid revocati subkey, or by a (deprecated) Revocation Key, should be considered valid Revocati
on signatures.</t> on Signatures.</t>
</section>
</section> <section anchor="sigtype-certification-revocation">
<section anchor="sigtype-certification-revocation"><name>Certification revocatio <name>Certification Revocation Signature (Type ID 0x30)</name>
n signature (type ID 0x30)</name> <t>This signature revokes an earlier User ID certification signature
(Type IDs 0x10 through 0x13) or Direct Key signature (Type ID 0x1F).
<t>This signature revokes an earlier User ID certification signature (signature
class 0x10 through 0x13) or direct key signature (0x1F).
It should be issued by the same key that issued the revoked signature or by a (d eprecated) Revocation Key. It should be issued by the same key that issued the revoked signature or by a (d eprecated) Revocation Key.
The signature is computed over the same data as the certification that it revoke The signature is computed over the same data as the certification that it revoke
s, and should have a later creation date than that certification.</t> s, and it should have a later creation date than that certification.</t>
</section>
</section> <section anchor="sigtype-timestamp">
<section anchor="sigtype-timestamp"><name>Timestamp signature (type ID 0x40)</na <name>Timestamp Signature (Type ID 0x40)</name>
me> <t>This signature is only meaningful for the timestamp contained in
it.</t>
<t>This signature is only meaningful for the timestamp contained in it.</t> </section>
<section anchor="sigtype-third-party-confirmation">
</section> <name>Third-Party Confirmation Signature (Type ID 0x50)</name>
<section anchor="sigtype-third-party-confirmation"><name>Third-Party Confirmatio <t>This signature is a signature over another OpenPGP Signature pack
n signature (type ID 0x50)</name> et.
It is analogous to a notary seal on the signed data. A Third-Party Confirmatio
<t>This signature is a signature over some other OpenPGP Signature packet(s). n signature <bcp14>SHOULD</bcp14> include a Signature Target subpacket that iden
It is analogous to a notary seal on the signed data. tifies the confirmed signature. <!--Note that we really do mean <bcp14>SHOULD</b
A third-party signature <bcp14>SHOULD</bcp14> include Signature Target subpacket cp14>.
(s) to give easy identification. There are plausible uses for this (such as a blind party that only sees the sign
Note that we really do mean <bcp14>SHOULD</bcp14>. ature, not the key or source document) that cannot include a target subpacket.--
There are plausible uses for this (such as a blind party that only sees the sign ></t>
ature, not the key or source document) that cannot include a target subpacket.</ </section>
t> <section anchor="sigtype-reserved">
<name>Reserved (Type ID 0xFF)</name>
</section> <t>An implementation <bcp14>MUST NOT</bcp14> create any signature wi
<section anchor="sigtype-reserved"><name>Reserved (type ID 0xFF)</name> th this type and <bcp14>MUST NOT</bcp14> validate any signature made with this t
ype.
<t>An implementation <bcp14>MUST NOT</bcp14> create any signature with this type
, and <bcp14>MUST NOT</bcp14> validate any signature made with this type.
See <xref target="sig-computation-notes"/> for more details.</t> See <xref target="sig-computation-notes"/> for more details.</t>
</section>
</section> </section>
</section> <section anchor="version-three-sig">
<section anchor="version-three-sig"><name>Version 3 Signature Packet Format</nam <name>Version 3 Signature Packet Format</name>
e> <t>The body of a version 3 Signature packet contains:</t>
<ul spacing="normal">
<t>The body of a version 3 Signature packet contains:</t> <li>
<t>A 1-octet version number with value 3.</t>
<t><list style="symbols"> </li>
<t>One-octet version number (3).</t> <li>
<t>One-octet length of following hashed material. <t>A 1-octet length of the following hashed material; it
<bcp14>MUST</bcp14> be 5. <list style="symbols"> <bcp14>MUST</bcp14> be 5: </t>
<t>One-octet signature type ID.</t> <ul spacing="normal">
<t>Four-octet creation time.</t> <li>
</list></t> <t>A 1-octet Signature Type ID.</t>
<t>Eight-octet Key ID of signer.</t> </li>
<t>One-octet public-key algorithm.</t> <li>
<t>One-octet hash algorithm.</t> <t>A 4-octet creation time.</t>
<t>Two-octet field holding left 16 bits of signed hash value.</t> </li>
<t>One or more multiprecision integers comprising the signature. </ul>
This portion is algorithm-specific, as described below.</t> </li>
</list></t> <li>
<t>An 8-octet Key ID of the signer.</t>
<t>The concatenation of the data to be signed, the signature type, and creation </li>
time from the Signature packet (5 additional octets) is hashed. <li>
<t>A 1-octet public key algorithm.</t>
</li>
<li>
<t>A 1-octet hash algorithm.</t>
</li>
<li>
<t>A 2-octet field holding left 16 bits of the signed hash value.<
/t>
</li>
<li>
<t>One or more MPIs comprising the signature. This portion is algo
rithm specific, as described below.</t>
</li>
</ul>
<t>The concatenation of the data to be signed, the signature type, and
the creation time from the Signature packet (5 additional octets) is hashed.
The resulting hash value is used in the signature algorithm. The resulting hash value is used in the signature algorithm.
The high 16 bits (first two octets) of the hash are included in the Signature pa cket to provide a way to reject some invalid signatures without performing a sig nature verification.</t> The high 16 bits (first two octets) of the hash are included in the Signature pa cket to provide a way to reject some invalid signatures without performing a sig nature verification.</t>
<t>Algorithm-specific fields for RSA signatures:</t>
<t>Algorithm-Specific Fields for RSA signatures:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>MPI of RSA signature value m<sup>d</sup> mod n.</t>
<t>Multiprecision integer (MPI) of RSA signature value m**d mod n.</t> </li>
</list></t> </ul>
<t>Algorithm-specific fields for DSA signatures:</t>
<t>Algorithm-Specific Fields for DSA signatures:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>MPI of DSA value r.</t>
<t>MPI of DSA value r.</t> </li>
<t>MPI of DSA value s.</t> <li>
</list></t> <t>MPI of DSA value s.</t>
</li>
<t>The signature calculation is based on a hash of the signed data, as described </ul>
above. <t>The signature calculation is based on a hash of the signed data, as
The details of the calculation are different for DSA signatures than for RSA sig described above.
natures, see <xref target="sig-rsa"/> and <xref target="sig-dsa"/>.</t> The details of the calculation are different for DSA signatures than for RSA sig
natures; see Sections <xref target="sig-rsa" format="counter"/> and <xref target
</section> ="sig-dsa" format="counter"/>.</t>
<section anchor="version-four-and-six-sig"><name>Version 4 and 6 Signature Packe </section>
t Formats</name> <section anchor="version-four-and-six-sig">
<name>Versions 4 and 6 Signature Packet Formats</name>
<t>The body of a v4 or v6 Signature packet contains:</t> <t>The body of a version 4 or version 6 Signature packet contains:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>One-octet version number. <t>A 1-octet version number.
This is 4 for v4 signatures and 6 for v6 signatures.</t> This is 4 for version 4 signatures and 6 for version 6 signatures.</t>
<t>One-octet signature type ID.</t> </li>
<t>One-octet public-key algorithm.</t> <li>
<t>One-octet hash algorithm.</t> <t>A 1-octet Signature Type ID.</t>
<t>A scalar octet count for the hashed subpacket data that follows this field. </li>
For a v4 signature, this is a two-octet field. <li>
For a v6 signature, this is a four-octet field. <t>A 1-octet public key algorithm.</t>
</li>
<li>
<t>A 1-octet hash algorithm.</t>
</li>
<li>
<t>A scalar octet count for the hashed subpacket data that follows
this field. For a version 4 signature, this is a 2-octet field.
For a version 6 signature, this is a 4-octet field.
Note that this is the length in octets of all of the hashed subpackets; an imple mentation's pointer incremented by this number will skip over the hashed subpack ets.</t> Note that this is the length in octets of all of the hashed subpackets; an imple mentation's pointer incremented by this number will skip over the hashed subpack ets.</t>
<t>Hashed subpacket data set (zero or more subpackets).</t> </li>
<t>A scalar octet count for the unhashed subpacket data that follows this fiel <li>
d. <t>A hashed subpacket data set (zero or more subpackets).</t>
For a v4 signature, this is a two-octet field. </li>
For a v6 signature, this is a four-octet field. <li>
<t>A scalar octet count for the unhashed subpacket data that follo
ws this field.
For a version 4 signature, this is a 2-octet field.
For a version 6 signature, this is a 4-octet field.
Note that this is the length in octets of all of the unhashed subpackets; an imp lementation's pointer incremented by this number will skip over the unhashed sub packets.</t> Note that this is the length in octets of all of the unhashed subpackets; an imp lementation's pointer incremented by this number will skip over the unhashed sub packets.</t>
<t>Unhashed subpacket data set (zero or more subpackets).</t> </li>
<t>Two-octet field holding the left 16 bits of the signed hash value.</t> <li>
<t>Only for v6 signatures, a variable-length field containing: <list style="s <t>An unhashed subpacket data set (zero or more subpackets).</t>
ymbols"> </li>
<t>A one-octet salt size. The value <bcp14>MUST</bcp14> match the value de <li>
fined for the hash algorithm as specified in <xref target="hash-algorithms-regis <t>A 2-octet field holding the left 16 bits of the signed hash val
try"/>.</t> ue.</t>
<t>The salt; a random value of the specified size.</t> </li>
</list></t> <li>
<t>One or more multiprecision integers comprising the signature. <t>Only for version 6 signatures, a variable-length field containi
This portion is algorithm-specific:</t> ng: </t>
</list></t> <ul spacing="normal">
<li>
<section anchor="sig-rsa"><name>Algorithm-Specific Fields for RSA signatures</na <t>A 1-octet salt size. The value <bcp14>MUST</bcp14> match th
me> e value defined for the hash algorithm as specified in <xref target="hash-algori
thms-registry"/>.</t>
<t><list style="symbols"> </li>
<t>Multiprecision integer (MPI) of RSA signature value m**d mod n.</t> <li>
</list></t> <t>The salt, which is a random value of the specified size.</t
>
<t>With RSA signatures, the hash value is encoded using PKCS#1 encoding type EMS </li>
A-PKCS1-v1_5 as described in <xref section="9.2" sectionFormat="of" target="RFC8 </ul>
017"/> (see also <xref target="emsa-pkcs1-v1-5"/>). </li>
<li>
<t>One or more MPIs comprising the signature.
This portion is algorithm specific.</t>
</li>
</ul>
<section anchor="sig-rsa">
<name>Algorithm-Specific Fields for RSA Signatures</name>
<ul spacing="normal">
<li>
<t>MPI of RSA signature value m<sup>d</sup> mod n.</t>
</li>
</ul>
<t>With RSA signatures, the hash value is encoded using PKCS#1 encod
ing type EMSA-PKCS1-v1_5, as described in <xref section="9.2" sectionFormat="of"
target="RFC8017"/> (see also <xref target="emsa-pkcs1-v1-5"/>).
This requires inserting the hash value as an octet string into an ASN.1 structur e. This requires inserting the hash value as an octet string into an ASN.1 structur e.
The object identifier (OID) for the hash algorithm itself is also included in th The object identifier (OID) for the hash algorithm itself is also included in th
e structure, see the OIDs in <xref target="emsa-hash-oids-registry"/>.</t> e structure; see the OIDs in <xref target="emsa-hash-oids-registry"/>.</t>
</section>
</section> <section anchor="sig-dsa">
<section anchor="sig-dsa"><name>Algorithm-Specific Fields for DSA or ECDSA signa <name>Algorithm-Specific Fields for DSA or ECDSA Signatures</name>
tures</name> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>MPI of DSA or ECDSA value r.</t>
<t>MPI of DSA or ECDSA value r.</t> </li>
<t>MPI of DSA or ECDSA value s.</t> <li>
</list></t> <t>MPI of DSA or ECDSA value s.</t>
</li>
<t>A version 3 signature <bcp14>MUST NOT</bcp14> be created and <bcp14>MUST NOT< </ul>
/bcp14> be used with ECDSA.</t> <t>A version 3 signature <bcp14>MUST NOT</bcp14> be created and <bcp
14>MUST NOT</bcp14> be used with the Elliptic Curve Digital Signature Algorithm
<t>A DSA signature <bcp14>MUST</bcp14> use a hash algorithm with a digest size o (ECDSA).</t>
f at least the number of bits of q, the group generated by the DSA key's generat <t>A DSA signature <bcp14>MUST</bcp14> use a hash algorithm with a d
or value.</t> igest size of at least the number of bits of q, the group generated by the DSA k
ey's generator value.</t>
<t>If the output size of the chosen hash is larger than the number of bits of q, <t>If the output size of the chosen hash is larger than the number o
the hash result is truncated to fit by taking the number of leftmost bits equal f bits of q, the hash result is truncated to fit by taking the number of leftmos
to the number of bits of q. t bits equal to the number of bits of q.
This (possibly truncated) hash function result is treated as a number and used d irectly in the DSA signature algorithm.</t> This (possibly truncated) hash function result is treated as a number and used d irectly in the DSA signature algorithm.</t>
<t>An ECDSA signature <bcp14>MUST</bcp14> use a hash algorithm with
<t>An ECDSA signature <bcp14>MUST</bcp14> use a hash algorithm with a digest siz a digest size of at least the curve's "fsize" value (see <xref target="ec-curves
e of at least the curve's "fsize" value (see <xref target="ec-curves"/>), except "/>), except in the case of NIST P-521, for which at least a 512-bit hash algori
in the case of NIST P-521, for which at least a 512-bit hash algorithm <bcp14>M thm <bcp14>MUST</bcp14> be used.</t>
UST</bcp14> be used.</t> </section>
<section anchor="sig-eddsa-legacy">
</section> <name>Algorithm-Specific Fields for EdDSALegacy Signatures (Deprecat
<section anchor="sig-eddsa-legacy"><name>Algorithm-Specific Fields for EdDSALega ed)</name>
cy signatures (deprecated)</name> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>Two MPI-encoded values, whose contents and formatting depend
<t>Two MPI-encoded values, whose contents and formatting depend on the choice on the choice of curve used (see <xref target="curve-specific-formats"/>).</t>
of curve used (see <xref target="curve-specific-formats"/>).</t> </li>
</list></t> </ul>
<t>A version 3 signature <bcp14>MUST NOT</bcp14> be created and <bcp
<t>A version 3 signature <bcp14>MUST NOT</bcp14> be created and <bcp14>MUST NOT< 14>MUST NOT</bcp14> be used with EdDSALegacy.</t>
/bcp14> be used with EdDSALegacy.</t> <t>An EdDSALegacy signature <bcp14>MUST</bcp14> use a hash algorithm
with a digest size of at least the curve's "fsize" value (see <xref target="ec-
<t>An EdDSALegacy signature <bcp14>MUST</bcp14> use a hash algorithm with a dige curves"/>).
st size of at least the curve's "fsize" value (see <xref target="ec-curves"/>).
A verifying implementation <bcp14>MUST</bcp14> reject any EdDSALegacy signature that uses a hash algorithm with a smaller digest size.</t> A verifying implementation <bcp14>MUST</bcp14> reject any EdDSALegacy signature that uses a hash algorithm with a smaller digest size.</t>
<section anchor="algorithm-specific-fields-for-ed25519legacy-signatu
<section anchor="algorithm-specific-fields-for-ed25519legacy-signatures-deprecat res-deprecated">
ed"><name>Algorithm-Specific Fields for Ed25519Legacy signatures (deprecated)</n <name>Algorithm-Specific Fields for Ed25519Legacy Signatures (Depr
ame> ecated)</name>
<t>The two MPIs for Ed25519Legacy represent the octet strings R an
<t>The two MPIs for Ed25519Legacy use octet strings R and S as described in <xre d S of the Edwards-curve Digital Signature Algorithm (EdDSA) described in <xref
f target="RFC8032"/>. target="RFC8032"/>.
Ed25519Legacy <bcp14>MUST NOT</bcp14> be used in signature packets version 6 or </t>
above.</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>MPI of an EC point R, represented as a (non-prefixed) nativ
<t>MPI of an EC point R, represented as a (non-prefixed) native (little-endian e (little-endian) octet string up to 32 octets.</t>
) octet string up to 32 octets.</t> </li>
<t>MPI of EdDSA value S, also in (non-prefixed) native (little-endian) format <li>
with a length up to 32 octets.</t> <t>MPI of EdDSA value S, also in (non-prefixed) native (little
</list></t> -endian) format with a length up to 32 octets.</t>
</li>
</section> </ul>
</section> <t>
<section anchor="sig-ed25519"><name>Algorithm-Specific Fields for Ed25519 signat Ed25519Legacy <bcp14>MUST NOT</bcp14> be used in Signature packets version 6 or
ures</name> above.
</t>
<t><list style="symbols"> </section>
<t>64 octets of the native signature.</t> </section>
</list></t> <section anchor="sig-ed25519">
<name>Algorithm-Specific Fields for Ed25519 Signatures</name>
<t>For more details, see <xref target="eddsa-notes"/>.</t> <ul spacing="normal">
<li>
<t>A version 3 signature <bcp14>MUST NOT</bcp14> be created and <bcp14>MUST NOT< <t>64 octets of the native signature.</t>
/bcp14> be used with Ed25519.</t> </li>
</ul>
<t>An Ed25519 signature <bcp14>MUST</bcp14> use a hash algorithm with a digest s <t>For more details, see <xref target="eddsa-notes"/>.</t>
ize of at least 256 bits. <t>A version 3 signature <bcp14>MUST NOT</bcp14> be created and <bcp
14>MUST NOT</bcp14> be used with Ed25519.</t>
<t>An Ed25519 signature <bcp14>MUST</bcp14> use a hash algorithm wit
h a digest size of at least 256 bits.
A verifying implementation <bcp14>MUST</bcp14> reject any Ed25519 signature that uses a hash algorithm with a smaller digest size.</t> A verifying implementation <bcp14>MUST</bcp14> reject any Ed25519 signature that uses a hash algorithm with a smaller digest size.</t>
</section>
</section> <section anchor="sig-ed448">
<section anchor="sig-ed448"><name>Algorithm-Specific Fields for Ed448 signatures <name>Algorithm-Specific Fields for Ed448 Signatures</name>
</name> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>114 octets of the native signature.</t>
<t>114 octets of the native signature.</t> </li>
</list></t> </ul>
<t>For more details, see <xref target="eddsa-notes"/>.</t>
<t>For more details, see <xref target="eddsa-notes"/>.</t> <t>A version 3 signature <bcp14>MUST NOT</bcp14> be created and <bcp
14>MUST NOT</bcp14> be used with Ed448.</t>
<t>A version 3 signature <bcp14>MUST NOT</bcp14> be created and <bcp14>MUST NOT< <t>An Ed448 signature <bcp14>MUST</bcp14> use a hash algorithm with
/bcp14> be used with Ed448.</t> a digest size of at least 512 bits.
<t>An Ed448 signature <bcp14>MUST</bcp14> use a hash algorithm with a digest siz
e of at least 512 bits.
A verifying implementation <bcp14>MUST</bcp14> reject any Ed448 signature that u ses a hash algorithm with a smaller digest size.</t> A verifying implementation <bcp14>MUST</bcp14> reject any Ed448 signature that u ses a hash algorithm with a smaller digest size.</t>
</section>
</section> <section anchor="notes-on-signatures">
<section anchor="notes-on-signatures"><name>Notes on Signatures</name> <name>Notes on Signatures</name>
<t>The concatenation of the data being signed, the signature data fr
<t>The concatenation of the data being signed, the signature data from the versi om the version number through the hashed subpacket data (inclusive), and (for si
on number through the hashed subpacket data (inclusive), and (for signature vers gnature versions later than 3) a 6-octet trailer (see <xref target="computing-si
ions later than 3) a six-octet trailer (see <xref target="computing-signatures"/ gnatures"/>) is hashed. The resulting hash value is what is signed. The high 16
>) is hashed. bits (first two octets) of the hash are included in the Signature packet to prov
The resulting hash value is what is signed. ide a way to reject some invalid signatures without performing a signature verif
The high 16 bits (first two octets) of the hash are included in the Signature pa ication. When verifying a version 6 signature, an implementation <bcp14>MUST</bc
cket to provide a way to reject some invalid signatures without performing a sig p14> reject the signature if these octets do not match the first two octets of t
nature verification. he computed hash.</t>
When verifying a v6 signature, an implementation <bcp14>MUST</bcp14> reject the <t>There are two fields consisting of Signature subpackets.
signature if these octets don't match the first two octets of the computed hash. The first field is hashed with the rest of the signature data, while the second
</t> is not hashed into the signature. The second set of subpackets (the "unhashed se
ction") is not cryptographically protected by the signature and should include o
<t>There are two fields consisting of Signature subpackets. nly advisory information. See <xref target="subpacket-section-guidance"/> for mo
The first field is hashed with the rest of the signature data, while the second re information.</t>
is not hashed into the signature. <t>The differences between a version 4 and version 6 signature are t
The second set of subpackets (the "unhashed section") is not cryptographically p wo-fold: first, a version 6 signature increases the width of the fields that ind
rotected by the signature and should include only advisory information. icate the size of the hashed and unhashed subpackets, making it possible to incl
See <xref target="subpacket-section-guidance"/> for more information.</t> ude significantly more data in subpackets.
<t>The differences between a v4 and v6 signature are two-fold: first, a v6 signa
ture increases the width of the fields that indicate the size of the hashed and
unhashed subpackets, making it possible to include significantly more data in su
bpackets.
Second, the hash is salted with random data (see <xref target="signature-salt-ra tionale"/>).</t> Second, the hash is salted with random data (see <xref target="signature-salt-ra tionale"/>).</t>
<t>The algorithms for converting the hash function result to a signa
<t>The algorithms for converting the hash function result to a signature are des ture are described in <xref target="computing-signatures"/>.</t>
cribed in <xref target="computing-signatures"/>.</t> </section>
<section anchor="signature-subpacket">
</section> <name>Signature Subpacket Specification</name>
<section anchor="signature-subpacket"><name>Signature Subpacket Specification</n <t>A subpacket data set consists of zero or more Signature subpacket
ame> s.
In Signature packets, the subpacket data set is preceded by a 2-octet (for versi
<t>A subpacket data set consists of zero or more Signature subpackets. on 4 signatures) or 4-octet (for version 6 signatures) scalar count of the lengt
In Signature packets, the subpacket data set is preceded by a two-octet (for v4 h in octets of all the subpackets.
signatures) or four-octet (for v6 signatures) scalar count of the length in octe
ts of all the subpackets.
A pointer incremented by this number will skip over the subpacket data set.</t> A pointer incremented by this number will skip over the subpacket data set.</t>
<t>Each subpacket consists of a subpacket header and a body.
<t>Each subpacket consists of a subpacket header and a body.
The header consists of:</t> The header consists of:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>The encoded subpacket length (1, 2, or 5 octets).
<t>The subpacket length (1, 2, or 5 octets),</t> </li>
<t>The encoded subpacket type ID (1 octet),</t> <li>The encoded Subpacket Type ID (1 octet).
</list></t> </li>
<li>The subpacket-specific data.
<t>and is followed by the subpacket-specific data.</t> </li>
</ul>
<t>The length includes the encoded subpacket type ID octet but not this length. <t>The subpacket length field covers the encoded Subpacket Type ID a
Its format is similar to the OpenPGP format packet header lengths, but cannot ha nd the subpacket-specific data, and it does not include the subpacket length fie
ve Partial Body Lengths. ld itself. It is encoded similarly to a 1-octet, 2-octet, or 5-octet OpenPGP for
That is:</t> mat packet header. The encoded subpacket length can be decoded as follows:</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
if the 1st octet < 192, then if the 1st octet < 192, then
lengthOfLength = 1 lengthOfLength = 1
subpacketLen = 1st_octet subpacketLen = 1st_octet
if the 1st octet >= 192 and < 255, then if the 1st octet >= 192 and < 255, then
lengthOfLength = 2 lengthOfLength = 2
subpacketLen = ((1st_octet - 192) << 8) + (2nd_octet) + 192 subpacketLen = ((1st_octet - 192) << 8) + (2nd_octet) + 192
if the 1st octet = 255, then if the 1st octet = 255, then
lengthOfLength = 5 lengthOfLength = 5
subpacket length = [four-octet scalar starting at 2nd_octet] subpacket length = [4-octet scalar starting at 2nd_octet]
]]></artwork></figure> ]]></artwork>
<t>Bit 7 of the encoded Subpacket Type ID is the "critical" bit.
<t>Bit 7 of the encoded subpacket type ID is the "critical" bit. If set, it denotes that the subpacket is one that is critical for the evaluator
If set, it denotes that the subpacket is one that is critical for the evaluator of the signature to recognize. If a subpacket is encountered that is marked crit
of the signature to recognize. ical but is unknown to the evaluating implementation, the evaluator <bcp14>SHOUL
If a subpacket is encountered that is marked critical but is unknown to the eval D</bcp14> consider the signature to be in error.</t>
uating implementation, the evaluator <bcp14>SHOULD</bcp14> consider the signatur <t>An implementation <bcp14>SHOULD</bcp14> ignore any non-critical s
e to be in error.</t> ubpacket of a type that it does not recognize.</t>
<t>An evaluator may "recognize" a subpacket but not implement it.
<t>An implementation <bcp14>SHOULD</bcp14> ignore any non-critical subpacket of
a type that it does not recognize.</t>
<t>An evaluator may "recognize" a subpacket, but not implement it.
The purpose of the critical bit is to allow the signer to tell an evaluator that it would prefer a new, unknown feature to generate an error rather than being i gnored.</t> The purpose of the critical bit is to allow the signer to tell an evaluator that it would prefer a new, unknown feature to generate an error rather than being i gnored.</t>
<t>The other bits of the encoded Subpacket Type ID (i.e., bits 6-0)
contain the Subpacket Type ID.</t>
<t>The following signature subpackets are defined:</t>
<table anchor="signature-subpacket-types-registry">
<name>OpenPGP Signature Subpacket Types Registry</name>
<thead>
<tr>
<th align="right">ID</th>
<th align="left">Description</th>
<th align="left">Reference</th>
</tr>
</thead>
<tbody>
<tr>
<td align="right">0</td>
<td align="left">Reserved</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">1</td>
<td align="left">Reserved</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">2</td>
<td align="left">Signature Creation Time</td>
<td align="left"><xref target="signature-creation-subpacket"/>
</td>
</tr>
<tr>
<td align="right">3</td>
<td align="left">Signature Expiration Time</td>
<td align="left"><xref target="signature-expiration-subpacket"
/></td>
</tr>
<tr>
<td align="right">4</td>
<td align="left">Exportable Certification</td>
<td align="left"> <xref target="exportable-certification-subpa
cket"/></td>
</tr>
<tr>
<td align="right">5</td>
<td align="left">Trust Signature</td>
<td align="left"><xref target="trust-signature-subpacket"/></t
d>
</tr>
<tr>
<td align="right">6</td>
<td align="left">Regular Expression</td>
<td align="left"><xref target="regex-subpacket"/></td>
</tr>
<tr>
<td align="right">7</td>
<td align="left">Revocable</td>
<td align="left"><xref target="revocable-subpacket"/></td>
</tr>
<tr>
<td align="right">8</td>
<td align="left">Reserved</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">9</td>
<td align="left">Key Expiration Time</td>
<td align="left"><xref target="key-expiration-subpacket"/></td
>
</tr>
<tr>
<td align="right">10</td>
<td align="left">Placeholder for backward compatibility</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">11</td>
<td align="left">Preferred Symmetric Ciphers for v1 SEIPD</td>
<td align="left"><xref target="preferred-v1-seipd"/></td>
</tr>
<tr>
<td align="right">12</td>
<td align="left">Revocation Key (deprecated)</td>
<td align="left"><xref target="revocation-key"/></td>
</tr>
<tr>
<td align="right">13-15</td>
<td align="left">Reserved</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">16</td>
<td align="left">Issuer Key ID</td>
<td align="left"><xref target="issuer-keyid-subpacket"/></td>
</tr>
<tr>
<td align="right">17-19</td>
<td align="left">Reserved</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">20</td>
<td align="left">Notation Data</td>
<td align="left"><xref target="notation-data"/></td>
</tr>
<tr>
<td align="right">21</td>
<td align="left">Preferred Hash Algorithms</td>
<td align="left"><xref target="preferred-hashes-subpacket"/></
td>
</tr>
<tr>
<td align="right">22</td>
<td align="left">Preferred Compression Algorithms</td>
<td align="left"><xref target="preferred-compression-subpacket
"/></td>
</tr>
<tr>
<td align="right">23</td>
<td align="left">Key Server Preferences</td>
<td align="left"><xref target="key-server-preferences"/></td>
</tr>
<tr>
<td align="right">24</td>
<td align="left">Preferred Key Server</td>
<td align="left"><xref target="preferred-key-server-subpacket"
/></td>
</tr>
<tr>
<td align="right">25</td>
<td align="left">Primary User ID</td>
<td align="left"><xref target="primary-user-id-subpacket"/></t
d>
</tr>
<tr>
<td align="right">26</td>
<td align="left">Policy URI</td>
<td align="left"><xref target="policy-uri-subpacket"/></td>
</tr>
<tr>
<td align="right">27</td>
<td align="left">Key Flags</td>
<td align="left"><xref target="key-flags"/></td>
</tr>
<tr>
<td align="right">28</td>
<td align="left">Signer's User ID</td>
<td align="left"><xref target="signers-user-id-subpacket"/></t
d>
</tr>
<tr>
<td align="right">29</td>
<td align="left">Reason for Revocation</td>
<td align="left"><xref target="reason-for-revocation"/></td>
</tr>
<tr>
<td align="right">30</td>
<td align="left">Features</td>
<td align="left"><xref target="features-subpacket"/></td>
</tr>
<tr>
<td align="right">31</td>
<td align="left">Signature Target</td>
<td align="left"><xref target="signature-target-subpacket"/></
td>
</tr>
<tr>
<td align="right">32</td>
<td align="left">Embedded Signature</td>
<td align="left"><xref target="embedded-signature-subpacket"/>
</td>
</tr>
<tr>
<td align="right">33</td>
<td align="left">Issuer Fingerprint</td>
<td align="left"><xref target="issuer-fingerprint-subpacket"/>
</td>
</tr>
<tr>
<td align="right">34</td>
<td align="left">Reserved</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">35</td>
<td align="left">Intended Recipient Fingerprint</td>
<td align="left"><xref target="intended-recipient-fingerprint"
/></td>
</tr>
<tr>
<td align="right">37</td>
<td align="left">Reserved (Attested Certifications)</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">38</td>
<td align="left">Reserved (Key Block)</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">39</td>
<td align="left">Preferred AEAD Ciphersuites</td>
<td align="left"><xref target="preferred-v2-seipd"/></td>
</tr>
<tr>
<td align="right">100-110</td>
<td align="left">Private or Experimental Use</td>
<td align="left"></td>
</tr>
</tbody>
</table>
<t>The other bits of the encoded subpacket type ID (i.e. bits 6-0) contain the s <t>Implementations <bcp14>SHOULD</bcp14> implement the four preferre
ubpacket type ID.</t> d algorithm subpackets (11, 21, 22, and 39), as well as the "Features" (30) and
"Reason for Revocation" (29) subpackets.
<t>The following signature subpackets are defined:</t> To avoid surreptitious forwarding (see <xref target="surreptitious-forwarding"/>
), implementations <bcp14>SHOULD</bcp14> also implement the "Intended Recipients
<texttable title="OpenPGP Signature Subpacket Types registry" anchor="signature- Fingerprint" (35) subpacket.
subpacket-types-registry">
<ttcol align='right'>ID</ttcol>
<ttcol align='left'>Description</ttcol>
<ttcol align='left'>Reference</ttcol>
<c>0</c>
<c>Reserved</c>
<c>&#160;</c>
<c>1</c>
<c>Reserved</c>
<c>&#160;</c>
<c>2</c>
<c>Signature Creation Time</c>
<c><xref target="signature-creation-subpacket"/></c>
<c>3</c>
<c>Signature Expiration Time</c>
<c><xref target="signature-expiration-subpacket"/></c>
<c>4</c>
<c>Exportable Certification</c>
<c><xref target="exportable-certification-subpacket"/></c>
<c>5</c>
<c>Trust Signature</c>
<c><xref target="trust-signature-subpacket"/></c>
<c>6</c>
<c>Regular Expression</c>
<c><xref target="regex-subpacket"/></c>
<c>7</c>
<c>Revocable</c>
<c><xref target="revocable-subpacket"/></c>
<c>8</c>
<c>Reserved</c>
<c>&#160;</c>
<c>9</c>
<c>Key Expiration Time</c>
<c><xref target="key-expiration-subpacket"/></c>
<c>10</c>
<c>Placeholder for backward compatibility</c>
<c>&#160;</c>
<c>11</c>
<c>Preferred Symmetric Ciphers for v1 SEIPD</c>
<c><xref target="preferred-v1-seipd"/></c>
<c>12</c>
<c>Revocation Key (deprecated)</c>
<c><xref target="revocation-key"/></c>
<c>13 to 15</c>
<c>Reserved</c>
<c>&#160;</c>
<c>16</c>
<c>Issuer Key ID</c>
<c><xref target="issuer-keyid-subpacket"/></c>
<c>17 to 19</c>
<c>Reserved</c>
<c>&#160;</c>
<c>20</c>
<c>Notation Data</c>
<c><xref target="notation-data"/></c>
<c>21</c>
<c>Preferred Hash Algorithms</c>
<c><xref target="preferred-hashes-subpacket"/></c>
<c>22</c>
<c>Preferred Compression Algorithms</c>
<c><xref target="preferred-compression-subpacket"/></c>
<c>23</c>
<c>Key Server Preferences</c>
<c><xref target="key-server-preferences"/></c>
<c>24</c>
<c>Preferred Key Server</c>
<c><xref target="preferred-key-server-subpacket"/></c>
<c>25</c>
<c>Primary User ID</c>
<c><xref target="primary-user-id-subpacket"/></c>
<c>26</c>
<c>Policy URI</c>
<c><xref target="policy-uri-subpacket"/></c>
<c>27</c>
<c>Key Flags</c>
<c><xref target="key-flags"/></c>
<c>28</c>
<c>Signer's User ID</c>
<c><xref target="signers-user-id-subpacket"/></c>
<c>29</c>
<c>Reason for Revocation</c>
<c><xref target="reason-for-revocation"/></c>
<c>30</c>
<c>Features</c>
<c><xref target="features-subpacket"/></c>
<c>31</c>
<c>Signature Target</c>
<c><xref target="signature-target-subpacket"/></c>
<c>32</c>
<c>Embedded Signature</c>
<c><xref target="embedded-signature-subpacket"/></c>
<c>33</c>
<c>Issuer Fingerprint</c>
<c><xref target="issuer-fingerprint-subpacket"/></c>
<c>34</c>
<c>Reserved</c>
<c>&#160;</c>
<c>35</c>
<c>Intended Recipient Fingerprint</c>
<c><xref target="intended-recipient-fingerprint"/></c>
<c>37</c>
<c>Reserved (Attested Certifications)</c>
<c>&#160;</c>
<c>38</c>
<c>Reserved (Key Block)</c>
<c>&#160;</c>
<c>39</c>
<c>Preferred AEAD Ciphersuites</c>
<c><xref target="preferred-v2-seipd"/></c>
<c>100 to 110</c>
<c>Private or experimental</c>
<c>&#160;</c>
</texttable>
<t>Implementations <bcp14>SHOULD</bcp14> implement the four preferred algorithm
subpackets (11, 21, 22, and 39), as well as the "Features" subpacket and the "Re
ason for Revocation" subpacket.
To avoid surreptitious forwarding (see <xref target="surreptitious-forwarding"/>
), implementations <bcp14>SHOULD</bcp14> also implement the "Intended Recipients
" subpacket.
Note that if an implementation chooses not to implement some of the preferences subpackets, it <bcp14>MUST</bcp14> default to the mandatory-to-implement algorit hms to ensure interoperability. Note that if an implementation chooses not to implement some of the preferences subpackets, it <bcp14>MUST</bcp14> default to the mandatory-to-implement algorit hms to ensure interoperability.
An encrypting implementation that does not implement the "Features" subpacket <b An encrypting implementation that does not implement the "Features" (30) subpack
cp14>SHOULD</bcp14> select the type of encrypted data format based instead on th et <bcp14>SHOULD</bcp14> select the type of encrypted data format based on the v
e versions of the recipient keys or external inference (see <xref target="cipher ersions of the recipient keys or external inference (see <xref target="ciphertex
text-malleability"/> for more details).</t> t-malleability"/> for more details).</t>
</section>
</section> <section anchor="signature-subpacket-types">
<section anchor="signature-subpacket-types"><name>Signature Subpacket Types</nam <name>Signature Subpacket Types</name>
e> <t>A number of subpackets are currently defined for OpenPGP signatur
es.
<t>A number of subpackets are currently defined for OpenPGP signatures.
Some subpackets apply to the signature itself and some are attributes of the key . Some subpackets apply to the signature itself and some are attributes of the key .
Subpackets that are found on a self-signature are placed on a certification made by the key itself. Subpackets that are found on a self-signature are placed on a certification made by the key itself.
Note that a key may have more than one User ID, and thus may have more than one Note that a key may have more than one User ID and thus may have more than one s
self-signature, and differing subpackets.</t> elf-signature and differing subpackets.</t>
<t>A subpacket may be found in either the hashed or the unhashed subpacket secti
<t>A subpacket may be found either in the hashed or unhashed subpacket sections ons of a signature. If a subpacket is not hashed, then the information in it can
of a signature. not be considered definitive because it is not covered by the cryptographic sign
If a subpacket is not hashed, then the information in it cannot be considered de ature. See <xref target="subpacket-section-guidance"/> for more discussion about
finitive because it is not part of the signature proper. hashed and unhashed subpackets.</t>
See <xref target="subpacket-section-guidance"/> for more discussion about hashed </section>
and unhashed subpackets.</t> <section anchor="notes-on-subpackets">
<name>Notes on Subpackets</name>
</section> <t>It is certainly possible for a signature to contain conflicting i
<section anchor="notes-on-subpackets"><name>Notes on Subpackets</name> nformation in subpackets.
For example, a signature may contain multiple copies of a preference or multiple
<t>It is certainly possible for a signature to contain conflicting information i expiration times. In most cases, an implementation <bcp14>SHOULD</bcp14> use th
n subpackets. e last subpacket in the hashed section of the signature, but it <bcp14>MAY</bcp1
For example, a signature may contain multiple copies of a preference or multiple 4> use any conflict resolution scheme that makes more sense. Please note that co
expiration times. nflict resolution is intentionally left to the implementer; most conflicts are s
In most cases, an implementation <bcp14>SHOULD</bcp14> use the last subpacket in imply syntax errors, and the ambiguous language here allows a receiver to be gen
the hashed section of the signature, but <bcp14>MAY</bcp14> use any conflict re erous in what they accept, while putting pressure on a creator to be stingy in w
solution scheme that makes more sense. hat they generate.</t>
Please note that we are intentionally leaving conflict resolution to the impleme <t>Some apparent conflicts may actually make sense. For example, sup
nter; most conflicts are simply syntax errors, and the wishy-washy language here pose a keyholder has a version 3 key and a version 4 key that share the same RSA
allows a receiver to be generous in what they accept, while putting pressure on key material. Either of these keys can verify a signature created by the other,
a creator to be stingy in what they generate.</t> and it may be reasonable for a signature to contain an Issuer Key ID subpacket
(<xref target="issuer-keyid-subpacket"/>) for each key, as a way of explicitly t
<t>Some apparent conflicts may actually make sense --- for example, suppose a ke ying those keys to the signature.</t>
yholder has a v3 key and a v4 key that share the same RSA key material. </section>
Either of these keys can verify a signature created by the other, and it may be <section anchor="self-sigs">
reasonable for a signature to contain an Issuer Key ID subpacket (<xref target=" <name>Notes on Self-Signatures</name>
issuer-keyid-subpacket"/>) for each key, as a way of explicitly tying those keys
to the signature.</t>
</section>
<section anchor="self-sigs"><name>Notes on Self-Signatures</name>
<t>A self-signature is a binding signature made by the key to which the signatur
e refers.
There are three types of self-signatures, the certification signatures (type IDs
0x10-0x13), the direct key signature (type ID 0x1F), and the subkey binding sig
nature (type ID 0x18).
A cryptographically-valid self-signature should be accepted from any primary key
, regardless of what Key Flags (<xref target="key-flags"/>) apply to the primary
key.
In particular, a primary key does not need to have 0x01 set in the first octet o
f Key Flags order to make a valid self-signature.</t>
<t>For certification self-signatures, each User ID <bcp14>MAY</bcp14> have a sel <t>A self-signature is a binding signature made by the key to which
f-signature, and thus different subpackets in those self-signatures. the signature refers. There are three types of self-signatures: the certificatio
For subkey binding signatures, each subkey <bcp14>MUST</bcp14> have a self-signa n signatures (Type IDs 0x10-0x13), the Direct Key signature (Type ID 0x1F), and
ture. the Subkey Binding signature (Type ID 0x18). A cryptographically valid self-sign
ature should be accepted from any primary key, regardless of what Key Flags (<xr
ef target="key-flags"/>) apply to the primary key.
In particular, a primary key does not need to have 0x01 set in the first octet o
f the Key Flags order to make a valid self-signature.</t>
<t>For certification self-signatures, each User ID <bcp14>MAY</bcp14
> have a self-signature and thus different subpackets in those self-signatures.
For Subkey Binding signatures, each subkey <bcp14>MUST</bcp14> have a self-signa
ture.
Subpackets that appear in a certification self-signature apply to the User ID, a nd subpackets that appear in the subkey self-signature apply to the subkey. Subpackets that appear in a certification self-signature apply to the User ID, a nd subpackets that appear in the subkey self-signature apply to the subkey.
Lastly, subpackets on the direct key signature apply to the entire key.</t> Lastly, subpackets on the Direct Key signature apply to the entire key.</t>
<t>An implementation should interpret a self-signature's preference
<t>An implementation should interpret a self-signature's preference subpackets a subpackets as narrowly as possible.
s narrowly as possible.
For example, suppose a key has two user names, Alice and Bob. For example, suppose a key has two user names, Alice and Bob.
Suppose that Alice prefers the AEAD ciphersuite AES-256 with OCB, and Bob prefer Suppose that Alice prefers the AEAD ciphersuite AES-256 with OCB, and Bob prefer
s Camellia-256 with GCM. s Camellia-256 with GCM. If the implementation locates this key via Alice's name
If the implementation locates this key via Alice's name, then the preferred AEAD , then the preferred AEAD ciphersuite is AES-256 with OCB; if the implementation
ciphersuite is AES-256 with OCB; if the implementation locates the key via Bob' locates the key via Bob's name, then the preferred algorithm is Camellia-256 wi
s name, then the preferred algorithm is Camellia-256 with GCM. th GCM.
If the key is located by Key ID, the algorithm of the primary User ID of the key If the key is located by Key ID, the algorithm of the Primary User ID of the key
provides the preferred AEAD ciphersuite.</t> provides the preferred AEAD ciphersuite.</t>
<t>Revoking a self-signature or allowing it to expire has a semantic
<t>Revoking a self-signature or allowing it to expire has a semantic meaning tha meaning that varies with the signature type.
t varies with the signature type.
Revoking the self-signature on a User ID effectively retires that user name. Revoking the self-signature on a User ID effectively retires that user name.
The self-signature is a statement, "My name X is tied to my signing key K" and i s corroborated by other users' certifications. The self-signature is a statement, "My name X is tied to my signing key K", and it is corroborated by other users' certifications.
If another user revokes their certification, they are effectively saying that th ey no longer believe that name and that key are tied together. If another user revokes their certification, they are effectively saying that th ey no longer believe that name and that key are tied together.
Similarly, if the users themselves revoke their self-signature, then the users n o longer go by that name, no longer have that email address, etc. Similarly, if the users themselves revoke their self-signature, then the users n o longer go by that name, no longer have that email address, etc.
Revoking a binding signature effectively retires that subkey. Revoking a binding signature effectively retires that subkey. Revoking a Direct
Revoking a direct key signature cancels that signature. Key signature cancels that signature.
Please see <xref target="reason-for-revocation"/> for more relevant detail.</t> Please see <xref target="reason-for-revocation"/> for more relevant details.</t>
<t>Since a self-signature contains important information about the k
<t>Since a self-signature contains important information about the key's use, an ey's use, an implementation <bcp14>SHOULD</bcp14> allow the user to rewrite the
implementation <bcp14>SHOULD</bcp14> allow the user to rewrite the self-signatu self-signature and important information in it, such as preferences and key expi
re, and important information in it, such as preferences and key expiration.</t> ration.</t>
<t>When an implementation imports a secret key, it <bcp14>SHOULD</bc
<t>When an implementation imports a secret key, it <bcp14>SHOULD</bcp14> verify p14> verify that the key's internal self-signatures do not advertise features or
that the key's internal self-signatures do not advertise features or algorithms algorithms that the implementation doesn't support.
that the implementation doesn't support.
If an implementation observes such a mismatch, it <bcp14>SHOULD</bcp14> warn the user and offer to create new self-signatures that advertise the actual set of f eatures and algorithms supported by the implementation.</t> If an implementation observes such a mismatch, it <bcp14>SHOULD</bcp14> warn the user and offer to create new self-signatures that advertise the actual set of f eatures and algorithms supported by the implementation.</t>
<t>An implementation that encounters multiple self-signatures on the
<t>An implementation that encounters multiple self-signatures on the same object same object <bcp14>MUST</bcp14> select the most recent valid self-signature and
<bcp14>MUST</bcp14> select the most recent valid self-signature, and ignore all ignore all other self-signatures.</t>
other self-signatures.</t> <t>By convention, a version 4 key stores information about the prima
ry Public Key (key flags, key expiration, etc.) and the Transferable Public Key
<t>By convention, a version 4 key stores information about the primary Public-Ke as a whole (features, algorithm preferences, etc.) in a User ID self-signature o
y (key flags, key expiration, etc.) and the Transferable Public Key as a whole ( f type 0x10 or 0x13. To use a version 4 key,
features, algorithm preferences, etc.) in a User ID self-signature of type 0x10 some implementations require at least one User ID with a valid self-signature to
or 0x13. be present.
Some implementations require at least one User ID with a valid self-signature to For this reason, it is <bcp14>RECOMMENDED</bcp14> to include at least one User I
be present to use a v4 key. D with a self-signature in version 4 keys.</t>
For this reason, it is <bcp14>RECOMMENDED</bcp14> to include at least one User I <t>For version 6 keys, it is <bcp14>RECOMMENDED</bcp14> to store inf
D with a self-signature in v4 keys.</t> ormation about the primary Public Key as well as the Transferable Public Key as
a whole (key flags, key expiration, features, algorithm preferences, etc.) in a
<t>For version 6 keys, it is <bcp14>RECOMMENDED</bcp14> to store information abo Direct Key signature (Type ID 0x1F) over the Public Key, instead of placing that
ut the primary Public-Key as well as the Transferable Public Key as a whole (key information in a User ID self-signature.
flags, key expiration, features, algorithm preferences, etc.) in a direct key s An implementation <bcp14>MUST</bcp14> ensure that a valid Direct Key signature i
ignature (type ID 0x1F) over the Public-Key instead of placing that information s present before using a version 6 key.
in a User ID self-signature. This prevents certain attacks where an adversary strips a self-signature specify
An implementation <bcp14>MUST</bcp14> ensure that a valid direct key signature i ing a Key Expiration Time or certain preferences.</t>
s present before using a v6 key. <t>An implementation <bcp14>SHOULD NOT</bcp14> require a User ID sel
This prevents certain attacks where an adversary strips a self-signature specify f-signature to be present in order to consume or use a key, unless the particula
ing a key expiration time or certain preferences.</t> r use is contingent on the keyholder identifying themselves with the textual lab
el in the User ID.
<t>An implementation <bcp14>SHOULD NOT</bcp14> require a User ID self-signature For example, when refreshing a key to learn about changes in expiration, adverti
to be present in order to consume or use a key, unless the particular use is con sed features, algorithm preferences, revocation, subkey rotation, and so forth,
tingent on the keyholder identifying themselves with the textual label in the Us there is no need to require a User ID self-signature. On the other hand, when ve
er ID. rifying a signature over an email message, an implementation <bcp14>MAY</bcp14>
For example, when refreshing a key to learn about changes in expiration, adverti choose to only accept a signature from a key that has a valid self-signature ove
sed features, algorithm preferences, revocation, subkey rotation, and so forth, r a User ID that matches the message's From: header, as a way to avoid a signatu
there is no need to require a User ID self-signature. re transplant attack.</t>
On the other hand, when verifying a signature over an e-mail message, an impleme
ntation <bcp14>MAY</bcp14> choose to only accept a signature from a key that has
a valid self-signature over a User ID that matches the message's From: header,
as a way to avoid a signature transplant attack.</t>
</section>
<section anchor="signature-creation-subpacket"><name>Signature Creation Time</na
me>
<t>(4-octet time field)</t>
<t>The time the signature was made.</t>
<t>This subpacket <bcp14>MUST</bcp14> be present in the hashed area.</t>
<t>When generating this subpacket, it <bcp14>SHOULD</bcp14> be marked as critica
l.</t>
</section> </section>
<section anchor="issuer-keyid-subpacket"><name>Issuer Key ID</name> <section anchor="signature-creation-subpacket">
<name>Signature Creation Time</name>
<t>(8-octet Key ID)</t> <t>(4-octet time field)</t>
<t>The time the signature was made.</t>
<t>The OpenPGP Key ID of the key issuing the signature. <t>This subpacket <bcp14>MUST</bcp14> be present in the hashed area.
</t>
<t>When generating this subpacket, it <bcp14>SHOULD</bcp14> be marke
d as critical.</t>
</section>
<section anchor="issuer-keyid-subpacket">
<name>Issuer Key ID</name>
<t>(8-octet Key ID)</t>
<t>The OpenPGP Key ID of the key issuing the signature.
If the version of that key is greater than 4, this subpacket <bcp14>MUST NOT</bc p14> be included in the signature. If the version of that key is greater than 4, this subpacket <bcp14>MUST NOT</bc p14> be included in the signature.
For these keys, consider the Issuer Fingerprint subpacket (<xref target="issuer- For these keys, consider the Issuer Fingerprint subpacket (<xref targ
fingerprint-subpacket"/>) instead.</t> et="issuer-fingerprint-subpacket"/>) instead.</t>
<t>Note: in previous versions of this specification, this subpacket was simply k
nown as the "Issuer" subpacket.</t>
</section>
<section anchor="key-expiration-subpacket"><name>Key Expiration Time</name>
<t>(4-octet time field)</t>
<t>The validity period of the key. <t>Note: in previous versions of this specification, this subpacket
was simply known as the "Issuer" subpacket.</t>
</section>
<section anchor="key-expiration-subpacket">
<name>Key Expiration Time</name>
<t>(4-octet time field)</t>
<t>The validity period of the key.
This is the number of seconds after the key creation time that the key expires. This is the number of seconds after the key creation time that the key expires.
For a direct or certification self-signature, the key creation time is that of t he primary key. For a direct or certification self-signature, the key creation time is that of t he primary key.
For a subkey binding signature, the key creation time is that of the subkey. For a Subkey Binding signature, the key creation time is that of the subkey.
If this is not present or has a value of zero, the key never expires. If this is not present or has a value of zero, the key never expires.
This is found only on a self-signature.</t> This is found only on a self-signature.</t>
<t>When an implementation generates this subpacket, it <bcp14>SHOULD
<t>When an implementation generates this subpacket, it <bcp14>SHOULD</bcp14> be </bcp14> be marked as critical.</t>
marked as critical.</t> </section>
<section anchor="preferred-v1-seipd">
</section> <name>Preferred Symmetric Ciphers for v1 SEIPD</name>
<section anchor="preferred-v1-seipd"><name>Preferred Symmetric Ciphers for v1 SE <t>(array of 1-octet values)</t>
IPD</name> <t>A series of Symmetric Cipher Algorithm IDs indicating how the key
holder prefers to receive the version 1 Symmetrically Encrypted and Integrity Pr
<t>(array of one-octet values)</t> otected Data packet (<xref target="version-one-seipd"/>).
<t>A series of symmetric cipher algorithm IDs indicating how the keyholder prefe
rs to receive version 1 Symmetrically Encrypted Integrity Protected Data (<xref
target="version-one-seipd"/>).
The subpacket body is an ordered list of octets with the most preferred listed f irst. The subpacket body is an ordered list of octets with the most preferred listed f irst.
It is assumed that only algorithms listed are supported by the recipient's imple mentation. It is assumed that only the algorithms listed are supported by the recipient's i mplementation.
Algorithm IDs are defined in <xref target="symmetric-algos"/>. Algorithm IDs are defined in <xref target="symmetric-algos"/>.
This is only found on a self-signature.</t> This is only found on a self-signature.</t>
<t>When generating a v2 SEIPD packet, this preference list is not re
<t>When generating a v2 SEIPD packet, this preference list is not relevant. levant.
See <xref target="preferred-v2-seipd"/> instead.</t> See <xref target="preferred-v2-seipd"/> instead.</t>
</section>
</section> <section anchor="preferred-v2-seipd">
<section anchor="preferred-v2-seipd"><name>Preferred AEAD Ciphersuites</name> <name>Preferred AEAD Ciphersuites</name>
<t>(array of pairs of octets indicating Symmetric Cipher and AEAD al
<t>(array of pairs of octets indicating Symmetric Cipher and AEAD algorithms)</t gorithms)</t>
> <t>A series of paired algorithm IDs indicating how the keyholder pre
fers to receive the version 2 Symmetrically Encrypted and Integrity Protected Da
<t>A series of paired algorithm IDs indicating how the keyholder prefers to rece ta packet (<xref target="version-two-seipd"/>).
ive version 2 Symmetrically Encrypted Integrity Protected Data (<xref target="ve
rsion-two-seipd"/>).
Each pair of octets indicates a combination of a symmetric cipher and an AEAD mo de that the keyholder prefers to use. Each pair of octets indicates a combination of a symmetric cipher and an AEAD mo de that the keyholder prefers to use.
The symmetric cipher algorithm ID precedes the AEAD algorithm ID in each pair. The Symmetric Cipher Algorithm ID precedes the AEAD algorithm ID in each pair.
The subpacket body is an ordered list of pairs of octets with the most preferred algorithm combination listed first.</t> The subpacket body is an ordered list of pairs of octets with the most preferred algorithm combination listed first.</t>
<t>It is assumed that only the combinations of algorithms listed are
<t>It is assumed that only the combinations of algorithms listed are supported b supported by the recipient's implementation, with the exception of the mandator
y the recipient's implementation, with the exception of the mandatory-to-impleme y-to-implement combination of AES-128 and OCB.
nt combination of AES-128 and OCB.
If AES-128 and OCB are not found in the subpacket, it is implicitly listed at th e end.</t> If AES-128 and OCB are not found in the subpacket, it is implicitly listed at th e end.</t>
<t>AEAD algorithm IDs are listed in <xref target="aead-algorithms"/>
<t>AEAD algorithm IDs are listed in <xref target="aead-algorithms"/>. .
Symmetric cipher algorithm IDs are listed in <xref target="symmetric-algos"/>.</ Symmetric Cipher Algorithm IDs are listed in <xref target="symmetric-algos"/>.</
t> t>
<t>For example, a subpacket containing the six octets</t>
<t>For example, a subpacket with content of these six octets:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
09 02 09 03 13 02 09 02 09 03 13 02
]]></artwork></figure> ]]></artwork>
<t>indicates that the keyholder prefers to receive v2 SEIPD using AE
<t>Indicates that the keyholder prefers to receive v2 SEIPD using AES-256 with O S-256 with OCB, then AES-256 with GCM, then Camellia-256 with OCB, and finally t
CB, then AES-256 with GCM, then Camellia-256 with OCB, and finally the implicit he implicit AES-128 with OCB.</t>
AES-128 with OCB.</t> <t>Note that support for the version 2 Symmetrically Encrypted and I
ntegrity Protected Data packet (<xref target="version-two-seipd"/>) in general i
<t>Note that support for version 2 of the Symmetrically Encrypted Integrity Prot s indicated by a Features Flag (<xref target="features-subpacket"/>).</t>
ected Data packet (<xref target="version-two-seipd"/>) in general is indicated b <t>This subpacket is only found on a self-signature.</t>
y a Features Flag (<xref target="features-subpacket"/>).</t> <t>When generating a v1 SEIPD packet, this preference list is not re
levant.
<t>This subpacket is only found on a self-signature.</t>
<t>When generating a v1 SEIPD packet, this preference list is not relevant.
See <xref target="preferred-v1-seipd"/> instead.</t> See <xref target="preferred-v1-seipd"/> instead.</t>
</section>
</section> <section anchor="preferred-hashes-subpacket">
<section anchor="preferred-hashes-subpacket"><name>Preferred Hash Algorithms</na <name>Preferred Hash Algorithms</name>
me> <t>(array of 1-octet values)</t>
<t>Message digest algorithm IDs that indicate which algorithms the k
<t>(array of one-octet values)</t> eyholder prefers to receive.
Like the Preferred AEAD Ciphersuites, the list is ordered.
<t>Message digest algorithm IDs that indicate which algorithms the keyholder pre
fers to receive.
Like the preferred AEAD ciphersuites, the list is ordered.
Algorithm IDs are defined in <xref target="hash-algos"/>. Algorithm IDs are defined in <xref target="hash-algos"/>.
This is only found on a self-signature.</t> This is only found on a self-signature.</t>
</section>
</section> <section anchor="preferred-compression-subpacket">
<section anchor="preferred-compression-subpacket"><name>Preferred Compression Al <name>Preferred Compression Algorithms</name>
gorithms</name> <t>(array of 1-octet values)</t>
<t>Compression algorithm IDs that indicate which algorithms the keyh
<t>(array of one-octet values)</t> older prefers to use.
Like the Preferred AEAD Ciphersuites, the list is ordered.
<t>Compression algorithm IDs that indicate which algorithms the keyholder prefer
s to use.
Like the preferred AEAD ciphersuites, the list is ordered.
Algorithm IDs are defined in <xref target="compression-algos"/>. Algorithm IDs are defined in <xref target="compression-algos"/>.
A zero, or the absence of this subpacket, denotes that uncompressed data is pref erred; the keyholder's implementation might have no compression support availabl e. A zero, or the absence of this subpacket, denotes that uncompressed data is pref erred; the keyholder's implementation might have no compression support availabl e.
This is only found on a self-signature.</t> This is only found on a self-signature.</t>
</section>
</section> <section anchor="signature-expiration-subpacket">
<section anchor="signature-expiration-subpacket"><name>Signature Expiration Time <name>Signature Expiration Time</name>
</name> <t>(4-octet time field)</t>
<t>The validity period of the signature.
<t>(4-octet time field)</t> This is the number of seconds after the Signature Creation Time that the signatu
re expires.
<t>The validity period of the signature.
This is the number of seconds after the signature creation time that the signatu
re expires.
If this is not present or has a value of zero, it never expires.</t> If this is not present or has a value of zero, it never expires.</t>
<t>When an implementation generates this subpacket, it <bcp14>SHOULD
<t>When an implementation generates this subpacket, it <bcp14>SHOULD</bcp14> be </bcp14> be marked as critical.</t>
marked as critical.</t> </section>
<section anchor="exportable-certification-subpacket">
</section> <name>Exportable Certification</name>
<section anchor="exportable-certification-subpacket"><name>Exportable Certificat <t>(1 octet of exportability, 0 for not, 1 for exportable)</t>
ion</name> <t>This subpacket denotes whether a certification signature is "expo
rtable"; it is intended for use by users other than the signature's issuer.
<t>(1 octet of exportability, 0 for not, 1 for exportable)</t>
<t>This subpacket denotes whether a certification signature is "exportable", to
be used by other users than the signature's issuer.
The packet body contains a Boolean flag indicating whether the signature is expo rtable. The packet body contains a Boolean flag indicating whether the signature is expo rtable.
If this packet is not present, the certification is exportable; it is equivalent to a flag containing a 1.</t> If this packet is not present, the certification is exportable; it is equivalent to a flag containing a 1.</t>
<t>Non-exportable, or "local", certifications are signatures made by
<t>Non-exportable, or "local", certifications are signatures made by a user to m a user to mark a key as valid within that user's implementation only.</t>
ark a key as valid within that user's implementation only.</t> <t>Thus, when an implementation prepares a user's copy of a key for
transport to another user (this is the process of "exporting" the key), any loca
<t>Thus, when an implementation prepares a user's copy of a key for transport to l certification signatures are deleted from the key.</t>
another user (this is the process of "exporting" the key), any local certificat <t>The receiver of a transported key "imports" it and likewise trims
ion signatures are deleted from the key.</t> any local certifications. In normal operation, there won't be any local certifi
cations, assuming the import is performed on an exported key. However, there are
<t>The receiver of a transported key "imports" it, and likewise trims any local instances where this can reasonably happen.
certifications.
In normal operation, there won't be any, assuming the import is performed on an
exported key.
However, there are instances where this can reasonably happen.
For example, if an implementation allows keys to be imported from a key database in addition to an exported key, then this situation can arise.</t> For example, if an implementation allows keys to be imported from a key database in addition to an exported key, then this situation can arise.</t>
<t>Some implementations do not represent the interest of a single us
<t>Some implementations do not represent the interest of a single user (for exam er (for example, a key server).
ple, a key server).
Such implementations always trim local certifications from any key they handle.< /t> Such implementations always trim local certifications from any key they handle.< /t>
<t>When an implementation generates this subpacket and denotes the s
<t>When an implementation generates this subpacket and denotes the signature as ignature as non-exportable, the subpacket <bcp14>MUST</bcp14> be marked as criti
non-exportable, the subpacket <bcp14>MUST</bcp14> be marked as critical.</t> cal.</t>
</section>
</section> <section anchor="revocable-subpacket">
<section anchor="revocable-subpacket"><name>Revocable</name> <name>Revocable</name>
<t>(1 octet of revocability, 0 for not, 1 for revocable)</t>
<t>(1 octet of revocability, 0 for not, 1 for revocable)</t> <t>A Signature's revocability status. The packet body contains a Boo
lean flag indicating whether the signature is revocable. Signatures that are not
<t>Signature's revocability status. revocable ignore any later Revocation Signatures. They represent the signer's c
The packet body contains a Boolean flag indicating whether the signature is revo ommitment that its signature cannot be revoked for the life of its key.
cable.
Signatures that are not revocable have any later revocation signatures ignored.
They represent a commitment by the signer that he cannot revoke his signature fo
r the life of his key.
If this packet is not present, the signature is revocable.</t> If this packet is not present, the signature is revocable.</t>
</section>
</section> <section anchor="trust-signature-subpacket">
<section anchor="trust-signature-subpacket"><name>Trust Signature</name> <name>Trust Signature</name>
<t>(1 octet "level" (depth), 1 octet of trust amount)</t>
<t>(1 octet "level" (depth), 1 octet of trust amount)</t> <t>The signer asserts that the key is not only valid but also trustw
orthy at the specified level. Level 0 has the same meaning as an ordinary validi
<t>Signer asserts that the key is not only valid but also trustworthy at the spe ty signature.
cified level.
Level 0 has the same meaning as an ordinary validity signature.
Level 1 means that the signed key is asserted to be a valid trusted introducer, with the 2nd octet of the body specifying the degree of trust. Level 1 means that the signed key is asserted to be a valid trusted introducer, with the 2nd octet of the body specifying the degree of trust.
Level 2 means that the signed key is asserted to be trusted to issue level 1 tru Level 2 means that the signed key is asserted to be trusted to issue level 1 Tru
st signatures; that is, the signed key is a "meta introducer". st Signatures; that is, the signed key is a "meta introducer".
Generally, a level n trust signature asserts that a key is trusted to issue leve Generally, a level n Trust Signature asserts that a key is trusted to issue leve
l n-1 trust signatures. l n-1 Trust Signatures.
The trust amount is in a range from 0-255, interpreted such that values less tha n 120 indicate partial trust and values of 120 or greater indicate complete trus t. The trust amount is in a range from 0-255, interpreted such that values less tha n 120 indicate partial trust and values of 120 or greater indicate complete trus t.
Implementations <bcp14>SHOULD</bcp14> emit values of 60 for partial trust and 12 0 for complete trust.</t> Implementations <bcp14>SHOULD</bcp14> emit values of 60 for partial trust and 12 0 for complete trust.</t>
</section>
</section> <section anchor="regex-subpacket">
<section anchor="regex-subpacket"><name>Regular Expression</name> <name>Regular Expression</name>
<t>(null-terminated UTF-8 encoded Regular Expression)</t>
<t>(null-terminated UTF-8 encoded regular expression)</t> <t>Used in conjunction with Trust Signature packets (of level &gt; 0
) to limit the scope of trust that is extended.
<t>Used in conjunction with trust Signature packets (of level &gt; 0) to limit t Only signatures by the target key on User IDs that match the Regular Expression
he scope of trust that is extended. in the body of this packet have trust extended by the Trust Signature subpacket.
Only signatures by the target key on User IDs that match the regular expression The Regular Expression uses the same syntax as Henry Spencer's "almost public do
in the body of this packet have trust extended by the trust Signature subpacket. main" Regular Expression <xref target="REGEX"/> package.
The regular expression uses the same syntax as Henry Spencer's "almost public do
main" regular expression <xref target="REGEX"/> package.
A description of the syntax is found in <xref target="regular-expressions"/>. A description of the syntax is found in <xref target="regular-expressions"/>.
The regular expression matches (or does not match) a sequence of UTF-8-encoded U nicode characters from User IDs. The Regular Expression matches (or does not match) a sequence of UTF-8-encoded U nicode characters from User IDs.
The expression itself is also written with UTF-8 characters.</t> The expression itself is also written with UTF-8 characters.</t>
<t>For historical reasons, this subpacket includes a null character
<t>For historical reasons, this subpacket includes a null character (octet with (an octet with value zero) after the Regular Expression.
value zero) after the regular expression. When an implementation parses a Regular Expression subpacket, it <bcp14>MUST</bc
When an implementation parses a regular expression subpacket, it <bcp14>MUST</bc p14> remove this octet; if it is not present, it <bcp14>MUST</bcp14> reject the
p14> remove this octet; if it is not present, it <bcp14>MUST</bcp14> reject the subpacket (i.e., ignore the subpacket if it's non-critical and reject the signat
subpacket (i.e. ignore the subpacket if it's non-critical and reject the signatu ure if it's critical).
re if it's critical). When an implementation generates a Regular Expression subpacket, it <bcp14>MUST<
When an implementation generates a regular expression subpacket, it <bcp14>MUST< /bcp14> include the null terminator.</t>
/bcp14> include the null terminator.</t> <t>When generating this subpacket, it <bcp14>SHOULD</bcp14> be marke
d as critical.</t>
<t>When generating this subpacket, it <bcp14>SHOULD</bcp14> be marked as critica </section>
l.</t> <section anchor="revocation-key">
<name>Revocation Key (Deprecated)</name>
</section> <t>(1 octet of class, 1 octet of public key algorithm ID, 20 octets
<section anchor="revocation-key"><name>Revocation Key</name> of version 4 fingerprint)</t>
<t>This mechanism is deprecated.
<t>(1 octet of class, 1 octet of public-key algorithm ID, 20 octets of v4 finger
print)</t>
<t>This mechanism is deprecated.
Applications <bcp14>MUST NOT</bcp14> generate such a subpacket.</t> Applications <bcp14>MUST NOT</bcp14> generate such a subpacket.</t>
<t>An application that wants the functionality of delegating revocat
<t>An application that wants the functionality of delegating revocation can use ion can use an escrowed Revocation Signature.
an escrowed Revocation Signature.
See <xref target="escrowed-revocations"/> for more details.</t> See <xref target="escrowed-revocations"/> for more details.</t>
<t>The remainder of this section describes how some implementations
<t>The remainder of this section describes how some implementations attempt to i attempt to interpret this deprecated subpacket.</t>
nterpret this deprecated subpacket.</t> <t>This packet was intended to authorize the specified key to issue
Revocation Signatures for this key. The class octet must have bit 0x80 set.
<t>This packet was intended to authorize the specified key to issue revocation s If bit 0x40 is set, it means the revocation information is sensitive.
ignatures for this key.
Class octet must have bit 0x80 set.
If the bit 0x40 is set, then this means that the revocation information is sensi
tive.
Other bits are for future expansion to other kinds of authorizations. Other bits are for future expansion to other kinds of authorizations.
This is only found on a direct key self-signature (type ID 0x1F). This is only found on a Direct Key self-signature (Type ID 0x1F).
The use on other types of self-signatures is unspecified.</t> The use on other types of self-signatures is unspecified.</t>
<t>If the "sensitive" flag is set, the keyholder feels this subpacke
<t>If the "sensitive" flag is set, the keyholder feels this subpacket contains p t contains private trust information that describes a real-world sensitive relat
rivate trust information that describes a real-world sensitive relationship. ionship.
If this flag is set, implementations <bcp14>SHOULD NOT</bcp14> export this signa If this flag is set, implementations <bcp14>SHOULD NOT</bcp14> export this signa
ture to other users except in cases where the data needs to be available: when t ture to other users except in cases where the data needs to be available, i.e.,
he signature is being sent to the designated revoker, or when it is accompanied when the signature is being sent to the designated revoker or when it is accompa
by a revocation signature from that revoker. nied by a Revocation Signature from that revoker.
Note that it may be appropriate to isolate this subpacket within a separate sign ature so that it is not combined with other subpackets that need to be exported. </t> Note that it may be appropriate to isolate this subpacket within a separate sign ature so that it is not combined with other subpackets that need to be exported. </t>
</section>
</section> <section anchor="notation-data">
<section anchor="notation-data"><name>Notation Data</name> <name>Notation Data</name>
<t>(4 octets of flags, 2 octets of name length (M), 2 octets of valu
<t>(4 octets of flags, 2 octets of name length (M), 2 octets of value length (N) e length (N), M octets of name data, N octets of value data)</t>
, M octets of name data, N octets of value data)</t> <t>This subpacket describes a "notation" on the signature that the i
ssuer wishes to make.
<t>This subpacket describes a "notation" on the signature that the issuer wishes
to make.
The notation has a name and a value, each of which are strings of octets. The notation has a name and a value, each of which are strings of octets.
There may be more than one notation in a signature. There may be more than one notation in a signature.
Notations can be used for any extension the issuer of the signature cares to mak e. Notations can be used for any extension the issuer of the signature cares to mak e.
The "flags" field holds four octets of flags.</t> The "flags" field holds 4 octets of flags.</t>
<t>All undefined flags <bcp14>MUST</bcp14> be zero.
<t>All undefined flags <bcp14>MUST</bcp14> be zero.
Defined flags are as follows:</t> Defined flags are as follows:</t>
<table anchor="sig-note-data-note-flags-registry">
<name>OpenPGP Signature Notation Data Subpacket Notation Flags Reg
istry</name>
<thead>
<tr>
<th align="left">Flag Position</th>
<th align="left">Shorthand</th>
<th align="left">Description</th>
<texttable title="OpenPGP Signature Notation Data Subpacket Notation Flags regis </tr>
try" anchor="sig-note-data-note-flags-registry"> </thead>
<ttcol align='left'>Flag Position</ttcol> <tbody>
<ttcol align='left'>Shorthand</ttcol> <tr>
<ttcol align='left'>Description</ttcol> <td align="left">0x80000000 (first bit of the first octet)</td
<ttcol align='left'>Reference</ttcol> >
<c>0x80000000 (first bit of first octet)</c> <td align="left">human-readable</td>
<c>human-readable</c> <td align="left">Notation value is UTF-8 text</td>
<c>Notation value is UTF-8 text.</c>
<c>This document</c>
</texttable>
<t>Notation names are arbitrary strings encoded in UTF-8.
They reside in two namespaces: The IETF namespace and the user namespace.</t>
<t>The IETF namespace is registered with IANA. </tr>
</tbody>
</table>
<t>Notation names are arbitrary strings encoded in UTF-8.
They reside in two namespaces: the IETF namespace and the user namespace.</t>
<t>The IETF namespace is registered with IANA.
These names <bcp14>MUST NOT</bcp14> contain the "@" character (0x40). These names <bcp14>MUST NOT</bcp14> contain the "@" character (0x40).
This is a tag for the user namespace.</t> This is a tag for the user namespace.</t>
<table anchor="sig-note-data-subpacket-types">
<name>OpenPGP Signature Notation Data Subpacket Types Registry</na
me>
<thead>
<tr>
<th align="left">Notation Name</th>
<th align="left">Data Type</th>
<th align="left">Allowed Values</th>
<texttable title="OpenPGP Signature Notation Data Subpacket Types registry" anch </tr>
or="sig-note-data-subpacket-types"> </thead>
<ttcol align='left'>Notation Name</ttcol> <tbody>
<ttcol align='left'>Data Type</ttcol> <tr>
<ttcol align='left'>Allowed Values</ttcol> <th colspan="3" align="left" rowspan="1">No registrations at th
<ttcol align='left'>Reference</ttcol> is time.</th>
<c>&#160;</c> </tr>
<c>&#160;</c> </tbody>
<c>&#160;</c> </table>
<c>&#160;</c> <t>This registry is initially empty.</t>
</texttable> <t>Names in the user namespace consist of a UTF-8 string tag followe
d by "@", followed by a DNS domain name.
<t>This registry is initially empty.</t>
<t>Names in the user namespace consist of a UTF-8 string tag followed by "@" fol
lowed by a DNS domain name.
Note that the tag <bcp14>MUST NOT</bcp14> contain an "@" character. Note that the tag <bcp14>MUST NOT</bcp14> contain an "@" character.
For example, the "sample" tag used by Example Corporation could be "sample@examp le.com".</t> For example, the "sample" tag used by Example Corporation could be "sample@examp le.com".</t>
<t>Names in a user space are owned and controlled by the owners of t
<t>Names in a user space are owned and controlled by the owners of that domain. hat domain.
Obviously, it's bad form to create a new name in a DNS space that you don't own. </t> Obviously, it's bad form to create a new name in a DNS space that you don't own. </t>
<t>Since the user namespace is in the form of an email address, impl
<t>Since the user namespace is in the form of an email address, implementers <bc ementers <bcp14>MAY</bcp14> wish to arrange for that address to reach a person w
p14>MAY</bcp14> wish to arrange for that address to reach a person who can be co ho can be consulted about the use of the named tag.
nsulted about the use of the named tag.
Note that due to UTF-8 encoding, not all valid user space name tags are valid em ail addresses.</t> Note that due to UTF-8 encoding, not all valid user space name tags are valid em ail addresses.</t>
<t>If there is a critical notation, the criticality applies to that
<t>If there is a critical notation, the criticality applies to that specific not specific notation and not to notations in general.</t>
ation and not to notations in general.</t> </section>
<section anchor="key-server-preferences">
</section> <name>Key Server Preferences</name>
<section anchor="key-server-preferences"><name>Key Server Preferences</name> <t>(N octets of flags)</t>
<t>This is a list of 1-bit flags that indicates preferences that the
<t>(N octets of flags)</t> keyholder has about how the key is handled on a key server.
<t>This is a list of one-bit flags that indicate preferences that the keyholder
has about how the key is handled on a key server.
All undefined flags <bcp14>MUST</bcp14> be zero.</t> All undefined flags <bcp14>MUST</bcp14> be zero.</t>
<table anchor="key-server-preference-flags-registry">
<texttable title="OpenPGP Key Server Preference Flags registry" anchor="key-serv <name>OpenPGP Key Server Preference Flags Registry</name>
er-preference-flags-registry"> <thead>
<ttcol align='left'>Flag</ttcol> <tr>
<ttcol align='left'>Shorthand</ttcol> <th align="left">Flag</th>
<ttcol align='left'>Definition</ttcol> <th align="left">Shorthand</th>
<c>0x80...</c> <th align="left">Definition</th>
<c>No-modify</c> </tr>
<c>The keyholder requests that this key only be modified or updated by the </thead>
keyholder or an administrator of the key server.</c> <tbody>
</texttable> <tr>
<td align="left">0x80...</td>
<t>This is found only on a self-signature.</t> <td align="left">No-modify</td>
<td align="left">The keyholder requests that this key only be
</section> modified or updated by the keyholder or an administrator of the key server.</td>
<section anchor="preferred-key-server-subpacket"><name>Preferred Key Server</nam </tr>
e> </tbody>
</table>
<t>(String)</t> <t>This is found only on a self-signature.</t>
</section>
<t>This is a URI of a key server that the keyholder prefers be used for updates. <section anchor="preferred-key-server-subpacket">
Note that keys with multiple User IDs can have a preferred key server for each U <name>Preferred Key Server</name>
ser ID. <t>(String)</t>
<t>This is a URI of a key server that the keyholder prefers be used
for updates.
Note that keys with multiple User IDs can have a Preferred Key Server for each U
ser ID.
Note also that since this is a URI, the key server can actually be a copy of the key retrieved by https, ftp, http, etc.</t> Note also that since this is a URI, the key server can actually be a copy of the key retrieved by https, ftp, http, etc.</t>
</section>
</section> <section anchor="primary-user-id-subpacket">
<section anchor="primary-user-id-subpacket"><name>Primary User ID</name> <name>Primary User ID</name>
<t>(1 octet, Boolean)</t>
<t>(1 octet, Boolean)</t> <t>This is a flag in a User ID's self-signature that states whether
this User ID is the main User ID for this key.
<t>This is a flag in a User ID's self-signature that states whether this User ID It is reasonable for an implementation to resolve ambiguities in preferences, fo
is the main User ID for this key. r example, by referring to the Primary User ID.
It is reasonable for an implementation to resolve ambiguities in preferences, fo
r example, by referring to the primary User ID.
If this flag is absent, its value is zero. If this flag is absent, its value is zero.
If more than one User ID in a key is marked as primary, the implementation may r esolve the ambiguity in any way it sees fit, but it is <bcp14>RECOMMENDED</bcp14 > that priority be given to the User ID with the most recent self-signature.</t> If more than one User ID in a key is marked as primary, the implementation may r esolve the ambiguity in any way it sees fit, but it is <bcp14>RECOMMENDED</bcp14 > that priority be given to the User ID with the most recent self-signature.</t>
<t>When appearing on a self-signature on a User ID packet, this subp
<t>When appearing on a self-signature on a User ID packet, this subpacket applie acket applies only to User ID packets.
s only to User ID packets. When appearing on a self-signature on a User Attribute packet, this subpacket ap
When appearing on a self-signature on a User Attribute packet, this subpacket ap plies only to User Attribute packets. That is, there are two different and indep
plies only to User Attribute packets. endent "primaries" -- one for User IDs and one for User Attributes.</t>
That is to say, there are two different and independent "primaries" --- one for </section>
User IDs, and one for User Attributes.</t> <section anchor="policy-uri-subpacket">
<name>Policy URI</name>
</section> <t>(String)</t>
<section anchor="policy-uri-subpacket"><name>Policy URI</name> <t>This subpacket contains a URI of a document that describes the po
licy under which the signature was issued.</t>
<t>(String)</t> </section>
<section anchor="key-flags">
<t>This subpacket contains a URI of a document that describes the policy under w <name>Key Flags</name>
hich the signature was issued.</t> <t>(N octets of flags)</t>
<t>This subpacket contains a list of binary flags that hold informat
</section> ion about a key.
<section anchor="key-flags"><name>Key Flags</name> It is a string of octets, and an implementation <bcp14>MUST NOT</bcp14> assume a
fixed size, so that it can grow over time. If a list is shorter than an impleme
<t>(N octets of flags)</t> ntation expects, the unstated flags are considered to be zero. The defined flags
are as follows:</t>
<t>This subpacket contains a list of binary flags that hold information about a <table anchor="key-flags-registry">
key. <name>OpenPGP Key Flags Registry</name>
It is a string of octets, and an implementation <bcp14>MUST NOT</bcp14> assume a <thead>
fixed size. <tr>
This is so it can grow over time. <th align="left">Flag</th>
If a list is shorter than an implementation expects, the unstated flags are cons <th align="left">Definition</th>
idered to be zero. </tr>
The defined flags are as follows:</t> </thead>
<tbody>
<texttable title="OpenPGP Key Flags registry" anchor="key-flags-registry"> <tr>
<ttcol align='left'>Flag</ttcol> <td align="left">0x01...</td>
<ttcol align='left'>Definition</ttcol> <td align="left">This key may be used to make User ID certific
<c>0x01...</c> ations (Signature Type IDs 0x10-0x13) or Direct Key signatures (Signature Type I
<c>This key may be used to make User ID certifications (signature type IDs D 0x1F) over other keys.</td>
0x10-0x13) or direct key signatures (signature type ID 0x1F) over other keys.</ </tr>
c> <tr>
<c>0x02...</c> <td align="left">0x02...</td>
<c>This key may be used to sign data.</c> <td align="left">This key may be used to sign data.</td>
<c>0x04...</c> </tr>
<c>This key may be used to encrypt communications.</c> <tr>
<c>0x08...</c> <td align="left">0x04...</td>
<c>This key may be used to encrypt storage.</c> <td align="left">This key may be used to encrypt communication
<c>0x10...</c> s.</td>
<c>The private component of this key may have been split by a secret-shari </tr>
ng mechanism.</c> <tr>
<c>0x20...</c> <td align="left">0x08...</td>
<c>This key may be used for authentication.</c> <td align="left">This key may be used to encrypt storage.</td>
<c>0x80...</c> </tr>
<c>The private component of this key may be in the possession of more than <tr>
one person.</c> <td align="left">0x10...</td>
<c>0x0004...</c> <td align="left">The private component of this key may have be
<c>Reserved (ADSK).</c> en split by a secret-sharing mechanism.</td>
<c>0x0008...</c> </tr>
<c>Reserved (timestamping).</c> <tr>
</texttable> <td align="left">0x20...</td>
<td align="left">This key may be used for authentication.</td>
<t>Usage notes:</t> </tr>
<tr>
<t>The flags in this packet may appear in self-signatures or in certification si <td align="left">0x80...</td>
gnatures. <td align="left">The private component of this key may be in t
They mean different things depending on who is making the statement --- for exam he possession of more than one person.</td>
ple, a certification signature that has the "sign data" flag is stating that the </tr>
certification is for that use. <tr>
On the other hand, the "communications encryption" flag in a self-signature is s <td align="left">0x0004...</td>
tating a preference that a given key be used for communications. <td align="left">Reserved (ADSK)</td>
Note however, that it is a thorny issue to determine what is "communications" an </tr>
d what is "storage". <tr>
This decision is left wholly up to the implementation; the authors of this docum <td align="left">0x0008...</td>
ent do not claim any special wisdom on the issue and realize that accepted opini <td align="left">Reserved (timestamping)</td>
on may change.</t> </tr>
</tbody>
<t>The "split key" (0x10) and "group key" (0x80) flags are placed on a self-sign </table>
ature only; they are meaningless on a certification signature. <t>Usage notes:</t>
They <bcp14>SHOULD</bcp14> be placed only on a direct key signature (type ID 0x1 <t>The flags in this packet may appear in self-signatures or in cert
F) or a subkey signature (type ID 0x18), one that refers to the key the flag app ification signatures. They mean different things depending on who is making the
lies to.</t> statement. For example, a certification signature that has the "sign data" flag
is stating that the certification is for that use. On the other hand, the "commu
<t>When an implementation generates this subpacket, it <bcp14>SHOULD</bcp14> be nications encryption" flag in a self-signature is stating a preference that a gi
marked as critical.</t> ven key be used for communications. However, note that determining what is "comm
unications" and what is "storage" is a thorny issue. This decision is left wholl
</section> y up to the implementation; the authors of this document do not claim any specia
<section anchor="signers-user-id-subpacket"><name>Signer's User ID</name> l wisdom on the issue and realize that accepted opinion may change.</t>
<t>The "split key" (0x10) and "group key" (0x80) flags are placed on
<t>(String)</t> a self-signature only; they are meaningless on a certification signature.
They <bcp14>SHOULD</bcp14> be placed only on a Direct Key signature (Type ID 0x1
<t>This subpacket allows a keyholder to state which User ID is responsible for t F) or a Subkey Binding signature (Type ID 0x18), one that refers to the key the
he signing. flag applies to.</t>
<t>When an implementation generates this subpacket, it <bcp14>SHOULD
</bcp14> be marked as critical.</t>
</section>
<section anchor="signers-user-id-subpacket">
<name>Signer's User ID</name>
<t>(String)</t>
<t>This subpacket allows a keyholder to state which User ID is respo
nsible for the signing.
Many keyholders use a single key for different purposes, such as business commun ications as well as personal communications. Many keyholders use a single key for different purposes, such as business commun ications as well as personal communications.
This subpacket allows such a keyholder to state which of their roles is making a signature.</t> This subpacket allows such a keyholder to state which of their roles is making a signature.</t>
<t>This subpacket is not appropriate to use to refer to a User Attri
<t>This subpacket is not appropriate to use to refer to a User Attribute packet. bute packet.</t>
</t> </section>
<section anchor="reason-for-revocation">
</section> <name>Reason for Revocation</name>
<section anchor="reason-for-revocation"><name>Reason for Revocation</name> <t>(1 octet of revocation code, N octets of reason string)</t>
<t>This subpacket is used only in Key Revocation and Certification R
<t>(1 octet of revocation code, N octets of reason string)</t> evocation signatures.
<t>This subpacket is used only in key revocation and certification revocation si
gnatures.
It describes the reason why the key or certification was revoked.</t> It describes the reason why the key or certification was revoked.</t>
<t>The first octet contains a machine-readable code that denotes the reason for the revocation:</t>
<t>The first octet contains a machine-readable code that denotes the reason for <table anchor="reason-for-revocation-code-registry">
the revocation:</t> <name>OpenPGP Reason for Revocation (Revocation Octet) Registry</n
ame>
<texttable title="OpenPGP Reason for Revocation Code registry" anchor="reason-fo <thead>
r-revocation-code-registry"> <tr>
<ttcol align='right'>Code</ttcol> <th align="right">Code</th>
<ttcol align='left'>Reason</ttcol> <th align="left">Reason</th>
<c>0</c> </tr>
<c>No reason specified (key revocations or cert revocations)</c> </thead>
<c>1</c> <tbody>
<c>Key is superseded (key revocations)</c> <tr>
<c>2</c> <td align="right">0</td>
<c>Key material has been compromised (key revocations)</c> <td align="left">No reason specified (Key Revocation or Certif
<c>3</c> ication Revocation signatures)</td>
<c>Key is retired and no longer used (key revocations)</c> </tr>
<c>32</c> <tr>
<c>User ID information is no longer valid (cert revocations)</c> <td align="right">1</td>
<c>100-110</c> <td align="left">Key is superseded (Key Revocation signatures)
<c>Private Use</c> </td>
</texttable> </tr>
<tr>
<t>Following the revocation code is a string of octets that gives information ab <td align="right">2</td>
out the Reason for Revocation in human-readable form (UTF-8). <td align="left">Key material has been compromised (Key Revoca
tion signatures)</td>
</tr>
<tr>
<td align="right">3</td>
<td align="left">Key is retired and no longer used (Key Revoca
tion signatures)</td>
</tr>
<tr>
<td align="right">32</td>
<td align="left">User ID information is no longer valid (Certi
fication Revocation signatures)</td>
</tr>
<tr>
<td align="right">100-110</td>
<td align="left">Private Use</td>
</tr>
</tbody>
</table>
<t>Following the revocation code is a string of octets that gives in
formation about the Reason for Revocation in human-readable form (UTF-8).
The string may be null (of zero length). The string may be null (of zero length).
The length of the subpacket is the length of the reason string plus one. The length of the subpacket is the length of the reason string plus one.
An implementation <bcp14>SHOULD</bcp14> implement this subpacket, include it in all revocation signatures, and interpret revocations appropriately. An implementation <bcp14>SHOULD</bcp14> implement this subpacket, include it in all Revocation Signatures, and interpret revocations appropriately.
There are important semantic differences between the reasons, and there are thus important reasons for revoking signatures.</t> There are important semantic differences between the reasons, and there are thus important reasons for revoking signatures.</t>
<t>If a key has been revoked because of a compromise, all signatures
<t>If a key has been revoked because of a compromise, all signatures created by created by that key are suspect. However, if it was merely superseded or retire
that key are suspect. d, old signatures are still valid. If the revoked signature is the self-signatur
However, if it was merely superseded or retired, old signatures are still valid. e for certifying a User ID, a revocation denotes that that user name is no longe
If the revoked signature is the self-signature for certifying a User ID, a revoc r in use.
ation denotes that that user name is no longer in use.
Such a signature revocation <bcp14>SHOULD</bcp14> include a Reason for Revocatio n subpacket containing code 32.</t> Such a signature revocation <bcp14>SHOULD</bcp14> include a Reason for Revocatio n subpacket containing code 32.</t>
<t>Note that any certification may be revoked, including a certifica
<t>Note that any signature may be revoked, including a certification on some oth tion on some other person's key. There are many good reasons for revoking a cert
er person's key. ification signature, such as the case where the keyholder leaves the employ of a
There are many good reasons for revoking a certification signature, such as the business with an email address. A revoked certification is no longer a part of
case where the keyholder leaves the employ of a business with an email address. validity calculations.</t>
A revoked certification is no longer a part of validity calculations.</t> </section>
<section anchor="features-subpacket">
</section> <name>Features</name>
<section anchor="features-subpacket"><name>Features</name> <t>(N octets of flags)</t>
<t>The Features subpacket denotes which advanced OpenPGP features a
<t>(N octets of flags)</t> user's implementation supports. This is so that as features are added to OpenPGP
that cannot be backward compatible, a user can state that they can use that fea
<t>The Features subpacket denotes which advanced OpenPGP features a user's imple ture. The flags are single bits that indicate that a given feature is supported.
mentation supports. </t>
This is so that as features are added to OpenPGP that cannot be backwards-compat <t>This subpacket is similar to a preferences subpacket and only app
ible, a user can state that they can use that feature. ears in a self-signature.</t>
The flags are single bits that indicate that a given feature is supported.</t> <t>An implementation <bcp14>SHOULD NOT</bcp14> use a feature listed
when sending to a user who does not state that they can use it, unless the imple
<t>This subpacket is similar to a preferences subpacket, and only appears in a s mentation can infer support for the feature from another implementation-dependen
elf-signature.</t> t mechanism.</t>
<t>Defined features are as follows:</t>
<t>An implementation <bcp14>SHOULD NOT</bcp14> use a feature listed when sending <t>First octet:</t>
to a user who does not state that they can use it, unless the implementation ca <table anchor="features-flags-registry">
n infer support for the feature from another implementation-dependent mechanism. <name>OpenPGP Features Flags Registry</name>
</t> <thead>
<tr>
<t>Defined features are as follows:</t> <th align="left">Feature</th>
<th align="left">Definition</th>
<t>First octet:</t> <th align="left">Reference</th>
</tr>
<texttable title="OpenPGP Features Flags registry" anchor="features-flags-regist </thead>
ry"> <tbody>
<ttcol align='left'>Feature</ttcol> <tr>
<ttcol align='left'>Definition</ttcol> <td align="left">0x01...</td>
<ttcol align='left'>Reference</ttcol> <td align="left">Version 1 Symmetrically Encrypted and Integri
<c>0x01...</c> ty Protected Data packet</td>
<c>Symmetrically Encrypted Integrity Protected Data packet version 1</c> <td align="left"><xref target="version-one-seipd"/></td>
<c><xref target="version-one-seipd"/></c> </tr>
<c>0x02...</c> <tr>
<c>Reserved</c> <td align="left">0x02...</td>
<c>&#160;</c> <td align="left">Reserved</td>
<c>0x04...</c> <td align="left"></td>
<c>Reserved</c> </tr>
<c>&#160;</c> <tr>
<c>0x08...</c> <td align="left">0x04...</td>
<c>Symmetrically Encrypted Integrity Protected Data packet version 2</c> <td align="left">Reserved</td>
<c><xref target="version-two-seipd"/></c> <td align="left"></td>
</texttable> </tr>
<tr>
<t>If an implementation implements any of the defined features, it <bcp14>SHOULD <td align="left">0x08...</td>
</bcp14> implement the Features subpacket, too.</t> <td align="left">Version 2 Symmetrically Encrypted and Integri
ty Protected Data packet</td>
<t>See <xref target="ciphertext-malleability"/> for details about how to use the <td align="left"><xref target="version-two-seipd"/></td>
Features subpacket when generating encryption data.</t> </tr>
</tbody>
</section> </table>
<section anchor="signature-target-subpacket"><name>Signature Target</name> <t>If an implementation implements any of the defined features, it <
bcp14>SHOULD</bcp14> implement the Features subpacket, too.</t>
<t>(1 octet public-key algorithm, 1 octet hash algorithm, N octets hash)</t> <t>See <xref target="ciphertext-malleability"/> for details about ho
w to use the Features subpacket when generating encryption data.</t>
<t>This subpacket identifies a specific target signature to which a signature re </section>
fers. <section anchor="signature-target-subpacket">
For revocation signatures, this subpacket provides explicit designation of which <name>Signature Target</name>
signature is being revoked. <t>(1 octet public key algorithm, 1 octet hash algorithm, N octets h
For a third-party or timestamp signature, this designates what signature is sign ash)</t>
ed. <t>This subpacket identifies a specific target signature to which a
signature refers.
For Revocation Signatures, this subpacket provides explicit designation of which
signature is being revoked. For a Third-Party Confirmation or Timestamp signatu
re, this designates what signature is signed.
All arguments are an identifier of that target signature.</t> All arguments are an identifier of that target signature.</t>
<t>The N octets of hash data <bcp14>MUST</bcp14> be the size of the
<t>The N octets of hash data <bcp14>MUST</bcp14> be the size of the hash of the signature's hash. For example, a target signature with a SHA-1 hash <bcp14>MUST<
signature. /bcp14> have 20 octets of hash data.</t>
For example, a target signature with a SHA-1 hash <bcp14>MUST</bcp14> have 20 oc </section>
tets of hash data.</t> <section anchor="embedded-signature-subpacket">
<name>Embedded Signature</name>
</section> <t>(1 Signature packet body)</t>
<section anchor="embedded-signature-subpacket"><name>Embedded Signature</name> <t>This subpacket contains a complete Signature packet body as speci
fied in <xref target="signature-packet"/>.
<t>(1 signature packet body)</t>
<t>This subpacket contains a complete Signature packet body as specified in <xre
f target="signature-packet"/>.
It is useful when one signature needs to refer to, or be incorporated in, anothe r signature.</t> It is useful when one signature needs to refer to, or be incorporated in, anothe r signature.</t>
</section>
</section> <section anchor="issuer-fingerprint-subpacket">
<section anchor="issuer-fingerprint-subpacket"><name>Issuer Fingerprint</name> <name>Issuer Fingerprint</name>
<t>(1 octet key version number, N octets of fingerprint)</t>
<t>(1 octet key version number, N octets of fingerprint)</t> <t>The OpenPGP Key fingerprint of the key issuing the signature.
<t>The OpenPGP Key fingerprint of the key issuing the signature.
This subpacket <bcp14>SHOULD</bcp14> be included in all signatures. This subpacket <bcp14>SHOULD</bcp14> be included in all signatures.
If the version of the issuing key is 4 and an Issuer Key ID subpacket (<xref tar If the version of the issuing key is 4 and an Issuer Key ID subpacket (<xref tar
get="issuer-keyid-subpacket"/>) is also included in the signature, the key ID of get="issuer-keyid-subpacket"/>) is also included in the signature, the Key ID of
the Issuer Key ID subpacket <bcp14>MUST</bcp14> match the low 64 bits of the fi the Issuer Key ID subpacket <bcp14>MUST</bcp14> match the low 64 bits of the fi
ngerprint.</t> ngerprint.</t>
<t>Note that the length N of the fingerprint for a version 4 key is
<t>Note that the length N of the fingerprint for a version 4 key is 20 octets; f 20 octets; for a version 6 key, N is 32.
or a version 6 key N is 32.
Since the version of the signature is bound to the version of the key, the versi on octet here <bcp14>MUST</bcp14> match the version of the signature. Since the version of the signature is bound to the version of the key, the versi on octet here <bcp14>MUST</bcp14> match the version of the signature.
If the version octet does not match the signature version, the receiving impleme ntation <bcp14>MUST</bcp14> treat it as a malformed signature (see <xref target= "malformed-signatures"/>).</t> If the version octet does not match the signature version, the receiving impleme ntation <bcp14>MUST</bcp14> treat it as a malformed signature (see <xref target= "malformed-signatures"/>).</t>
</section>
<section anchor="intended-recipient-fingerprint">
<name>Intended Recipient Fingerprint</name>
<t>(1 octet key version number, N octets of fingerprint)</t>
<t>The OpenPGP Key fingerprint of the intended recipient primary key
.
If one or more subpackets of this type are included in a signature, it <bcp14>SH
OULD</bcp14> be considered valid only in an encrypted context, where the key it
was encrypted to is one of the indicated primary keys or one of their subkeys. T
his can be used to prevent forwarding a signature outside of its intended, encry
pted context (see <xref target="surreptitious-forwarding"/>).</t>
<t>Note that the length N of the fingerprint for a version 4 key is
20 octets; for a version 6 key, N is 32.</t>
<t>An implementation <bcp14>SHOULD</bcp14> generate this subpacket w
hen creating a signed and encrypted message.</t>
<t>When generating this subpacket in a version 6 signature, it <bcp1
4>SHOULD</bcp14> be marked as critical.</t>
</section>
</section>
<section anchor="computing-signatures">
<name>Computing Signatures</name>
</section> <t>All signatures are formed by producing a hash over the signature da
<section anchor="intended-recipient-fingerprint"><name>Intended Recipient Finger ta and then using the resulting hash in the signature algorithm.</t>
print</name> <t>When creating or verifying a version 6 signature, the salt is fed i
nto the hash context before any other data.</t>
<t>(1 octet key version number, N octets of fingerprint)</t> <t>For binary document signatures (Type ID 0x00), the document data is
hashed directly.
<t>The OpenPGP Key fingerprint of the intended recipient primary key. For text document signatures (Type ID 0x01), the implementation <bcp14>MUST</bcp
If one or more subpackets of this type are included in a signature, it <bcp14>SH 14> first canonicalize the document by converting line endings to &lt;CR&gt;&lt;
OULD</bcp14> be considered valid only in an encrypted context, where the key it LF&gt; and encoding it in UTF-8 (see <xref target="RFC3629"/>).
was encrypted to is one of the indicated primary keys, or one of their subkeys. The resulting UTF-8 byte stream is hashed.</t>
This can be used to prevent forwarding a signature outside of its intended, encr <t>When a version 4 signature is made over a key, the hash data starts
ypted context (see <xref target="surreptitious-forwarding"/>).</t> with the octet 0x99, followed by a 2-octet length of the key, followed by the b
ody of the key packet.
<t>Note that the length N of the fingerprint for a version 4 key is 20 octets; f When a version 6 signature is made over a key, the hash data starts with the sal
or a version 6 key N is 32.</t> t and then octet 0x9B, followed by a 4-octet length of the key, followed by the
body of the key packet.</t>
<t>An implementation <bcp14>SHOULD</bcp14> generate this subpacket when creating <t>A Subkey Binding signature (Type ID 0x18) or Primary Key Binding si
a signed and encrypted message.</t> gnature (Type ID 0x19) then hashes the subkey using the same format as the main
key (also using 0x99 or 0x9B as the first octet). Primary Key Revocation signatu
<t>When generating this subpacket in a v6 signature, it <bcp14>SHOULD</bcp14> be res (Type ID 0x20) hash only the key being revoked.
marked as critical.</t> A Subkey Revocation signature (Type ID 0x28) first hashes the primary key and th
en the subkey being revoked.</t>
</section> <t>A Certification signature (Type IDs 0x10 through 0x13) hashes the User ID tha
</section> t is bound to the key into the hash context after the above data. A version 3 ce
<section anchor="computing-signatures"><name>Computing Signatures</name> rtification hashes the contents of the User ID or User Attribute packet without
the packet header. A version 4 or version 6 certification hashes the constant 0x
<t>All signatures are formed by producing a hash over the signature data, and th B4 for User ID certifications or the constant 0xD1 for User Attribute certificat
en using the resulting hash in the signature algorithm.</t> ions, followed by a 4-octet number giving the length of the User ID or User Attr
ibute data, followed by the User ID or User Attribute data.</t>
<t>When creating or verifying a v6 signature, the salt is fed into the hash cont
ext before any other data.</t>
<t>For binary document signatures (type ID 0x00), the document data is hashed di
rectly.
For text document signatures (type ID 0x01), the implementation <bcp14>MUST</bcp
14> first canonicalize the document by converting line endings to &lt;CR&gt;&lt;
LF&gt; and encoding it in UTF-8 (see <xref target="RFC3629"/>).
The resulting UTF-8 bytestream is hashed.</t>
<t>When a v4 signature is made over a key, the hash data starts with the octet 0
x99, followed by a two-octet length of the key, and then the body of the key pac
ket.
When a v6 signature is made over a key, the hash data starts with the salt, then
octet 0x9B, followed by a four-octet length of the key, and then the body of th
e key packet.</t>
<t>A subkey binding signature (type ID 0x18) or primary key binding signature (t
ype ID 0x19) then hashes the subkey using the same format as the main key (also
using 0x99 or 0x9B as the first octet).
Primary key revocation signatures (type ID 0x20) hash only the key being revoked
.
Subkey revocation signature (type ID 0x28) hash first the primary key and then t
he subkey being revoked.</t>
<t>A certification signature (type ID 0x10 through 0x13) hashes the User ID bein
g bound to the key into the hash context after the above data.
A v3 certification hashes the contents of the User ID or User Attribute packet,
without the packet header.
A v4 or v6 certification hashes the constant 0xB4 for User ID certifications or
the constant 0xD1 for User Attribute certifications, followed by a four-octet nu
mber giving the length of the User ID or User Attribute data, and then the User
ID or User Attribute data.</t>
<t>When a signature is made over a Signature packet (type ID 0x50, "Third-Party
Confirmation signature"), the hash data starts with the salt (v6 signatures only
), followed by the octet 0x88, followed by the four-octet length of the signatur
e, and then the body of the Signature packet.
(Note that this is a Legacy packet header for a Signature packet with the length
-of-length field set to zero.) The unhashed subpacket data of the Signature pack
et being hashed is not included in the hash, and the unhashed subpacket data len
gth value is set to zero.</t>
<t>Once the data body is hashed, then a trailer is hashed.
This trailer depends on the version of the signature.</t>
<t><list style="symbols">
<t>A v3 signature hashes five octets of the packet body, starting from the sig
nature type field.
This data is the signature type, followed by the four-octet signature creation t
ime.</t>
<t>A v4 or v6 signature hashes the packet body starting from its first field,
the version number, through the end of the hashed subpacket data and a final ext
ra trailer.
Thus, the hashed fields are: <list style="symbols">
<t>An octet indicating the signature version (0x04 for v4, 0x06 for v6),</
t>
<t>The signature type,</t>
<t>The public-key algorithm,</t>
<t>The hash algorithm,</t>
<t>The hashed subpacket length,</t>
<t>The hashed subpacket body,</t>
<t>A second version octet (0x04 for v4, 0x06 for v6)</t>
<t>A single octet 0xFF,</t>
<t>A number representing the length (in octets) of the hashed data from th
e Signature packet through the hashed subpacket body.
This a four-octet big-endian unsigned integer of the length modulo 2**32.</t>
</list></t>
</list></t>
<t>After all this has been hashed in a single hash context, the resulting hash f
ield is used in the signature algorithm and its first two octets are placed in t
he Signature packet, as described in <xref target="version-four-and-six-sig"/>.<
/t>
<t>For worked examples of the data hashed during a signature, see <xref target="
sig-hashed-data-example"/>.</t>
<section anchor="sig-computation-notes"><name>Notes About Signature Computation<
/name>
<t>The data actually hashed by OpenPGP varies depending on signature version, in <t>A Third-Party Confirmation signature (Type ID 0x50) hashes the salt (version
order to ensure that a signature made using one version cannot be repurposed as 6 signatures only), followed by the octet 0x88, followed by the 4-octet length o
a signature with a different version over subtly different data. f the signature, and then the body of the Signature packet. (Note that this is a
The hashed data streams differ based on their trailer, most critically in the fi Legacy packet header for a Signature packet with the length-of-length field set
fth and sixth octets from the end of the stream. to zero.) The unhashed subpacket data of the Signature packet being hashed is n
ot included in the hash, and the unhashed subpacket data length value is set to
zero.</t>
<t>Once the data body is hashed, then a trailer is hashed. This traile
r depends on the version of the signature.</t>
<ul spacing="normal">
<li>
<t>A version 3 signature hashes five octets of the packet body, st
arting from the signature type field. This data is the signature type, followed
by the 4-octet Signature Creation Time.</t>
</li>
<li>
<t>A version 4 or version 6 signature hashes the packet body start
ing from its first field, the version number, through the end of the hashed subp
acket data and a final extra trailer. Thus, the hashed fields are: </t>
<ul spacing="normal">
<li>
<t>an octet indicating the signature version (0x04 for version
4, and 0x06 for version 6),</t>
</li>
<li>
<t>the signature type,</t>
</li>
<li>
<t>the public key algorithm,</t>
</li>
<li>
<t>the hash algorithm,</t>
</li>
<li>
<t>the hashed subpacket length,</t>
</li>
<li>
<t>the hashed subpacket body,</t>
</li>
<li>
<t>a second version octet (0x04 for version 4, and 0x06 for ve
rsion 6),</t>
</li>
<li>
<t>a single octet 0xFF, and</t>
</li>
<li>
<t>a number representing the length (in octets) of the hashed
data from the Signature packet through the hashed subpacket body. This a 4-octet
big-endian unsigned integer of the length modulo 2<sup>32</sup>.</t>
</li>
</ul>
</li>
</ul>
<t>After all this has been hashed in a single hash context, the result
ing hash field is used in the signature algorithm, and its first two octets are
placed in the Signature packet, as described in <xref target="version-four-and-s
ix-sig"/>.</t>
<t>For worked examples of the data hashed during a signature, see <xre
f target="sig-hashed-data-example"/>.</t>
<section anchor="sig-computation-notes">
<name>Notes about Signature Computation</name>
<t>The data actually hashed by OpenPGP varies depending on the signa
ture version, in order to ensure that a signature made using one version cannot
be repurposed as a signature with a different version over subtly different data
. The hashed data streams differ based on their trailer, most critically in the
fifth and sixth octets from the end of the stream.
In particular:</t> In particular:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>A v3 signature uses the fifth octet from the end to store its signature typ <t>A version 3 signature uses the fifth octet from the end to st
e ID. ore its Signature Type ID.
This <bcp14>MUST NOT</bcp14> be signature type ID <spanx style="verb">0xFF</span This <bcp14>MUST NOT</bcp14> be Signature Type ID <tt>0xFF</tt>.</t>
x>.</t> </li>
<t>All signature versions later than v3 always use a literal <spanx style="ver <li>
b">0xFF</spanx> in the fifth octet from the end. <t>All signature versions later than version 3 always use a lite
For these later signature versions, the sixth octet from the end (the octet befo ral <tt>0xFF</tt> in the fifth octet from the end.
re the <spanx style="verb">0xFF</spanx>) stores the signature version number.</t For these later signature versions, the sixth octet from the end (the octet befo
> re the <tt>0xFF</tt>) stores the signature version number.</t>
</list></t> </li>
</ul>
</section> </section>
</section> </section>
<section anchor="malformed-signatures"><name>Malformed and Unknown Signatures</n <section anchor="malformed-signatures">
ame> <name>Malformed and Unknown Signatures</name>
<t>In some cases, a Signature packet (or its corresponding One-Pass Si
<t>In some cases, a signature packet (or its corresponding One-Pass Signature pa gnature packet; see <xref target="one-pass-sig"/>) may be malformed or unknown.
cket, see <xref target="one-pass-sig"/>) may be malformed or unknown.
For example, it might encounter any of the following problems (this is not an ex haustive list):</t> For example, it might encounter any of the following problems (this is not an ex haustive list):</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>An unknown signature type</t> <t>An unknown signature type</t>
<t>An unknown signature version</t> </li>
<t>An unsupported signature version</t> <li>
<t>An unknown "critical" subpacket (see <xref target="signature-subpacket"/>) <t>An unknown signature version</t>
in the hashed area</t> </li>
<t>A subpacket with a length that diverges from the expected length</t> <li>
<t>A hashed subpacket area with length that exceeds the length of the signatur <t>An unsupported signature version</t>
e packet itself</t> </li>
<t>A known-weak hash algorithm (e.g. MD5)</t> <li>
<t>A mismatch between the hash algorithm expected salt length and the actual s <t>An unknown "critical" subpacket (see <xref target="signature-su
alt length</t> bpacket"/>) in the hashed area</t>
<t>A mismatch between the One-Pass Signature version and the Signature version </li>
(see <xref target="signed-message-versions"/>)</t> <li>
<t>A signature with a version other than 6, made by a v6 key</t> <t>A subpacket with a length that diverges from the expected lengt
</list></t> h</t>
</li>
<t>When an implementation encounters such a malformed or unknown signature, it < <li>
bcp14>MUST</bcp14> ignore the signature for validation purposes. <t>A hashed subpacket area with length that exceeds the length of
the Signature packet itself</t>
</li>
<li>
<t>A hash algorithm known to be weak (e.g., MD5)</t>
</li>
<li>
<t>A mismatch between the expected salt length of the hash algorit
hm and the actual salt length</t>
</li>
<li>
<t>A mismatch between the One-Pass Signature version and the Signa
ture version (see <xref target="signed-message-versions"/>)</t>
</li>
<li>
<t>A signature with a version other than 6, made by a version 6 ke
y</t>
</li>
</ul>
<t>When an implementation encounters such a malformed or unknown signa
ture, it <bcp14>MUST</bcp14> ignore the signature for validation purposes.
It <bcp14>MUST NOT</bcp14> indicate a successful signature validation for such a signature. It <bcp14>MUST NOT</bcp14> indicate a successful signature validation for such a signature.
At the same time, it <bcp14>MUST NOT</bcp14> halt processing on the packet strea m or reject other signatures in the same packet stream just because an unknown o r invalid signature exists.</t> At the same time, it <bcp14>MUST NOT</bcp14> halt processing on the packet strea m or reject other signatures in the same packet stream just because an unknown o r invalid signature exists.</t>
<t>This requirement is necessary for forward compatibility.
<t>This requirement is necessary for forward-compatibility.
Producing an output that indicates that no successful signatures were found is p referable to aborting processing entirely.</t> Producing an output that indicates that no successful signatures were found is p referable to aborting processing entirely.</t>
</section>
</section> </section>
</section> <section anchor="skesk">
<section anchor="skesk"><name>Symmetric-Key Encrypted Session Key Packet (Type I <name>Symmetric Key Encrypted Session Key Packet (Type ID 3)</name>
D 3)</name> <t>The Symmetric Key Encrypted Session Key (SKESK) packet holds the symm
etric key encryption of a session key used to encrypt a message.
<t>The Symmetric-Key Encrypted Session Key (SKESK) packet holds the symmetric-ke Zero or more Public Key Encrypted Session Key packets (<xref target="pkesk"/>) a
y encryption of a session key used to encrypt a message. nd/or Symmetric Key Encrypted Session Key packets precede an encryption containe
Zero or more Public-Key Encrypted Session Key packets (<xref target="pkesk"/>) a r (that is, a Symmetrically Encrypted and Integrity Protected Data packet or --
nd/or Symmetric-Key Encrypted Session Key packets precede an encryption containe for historic data -- a Symmetrically Encrypted Data packet) that holds an Encryp
r (that is, a Symmetrically Encrypted Integrity Protected Data packet or --- for ted Message. The message is encrypted with a session key, and the session key is
historic data --- a Symmetrically Encrypted Data packet) that holds an encrypte itself encrypted and stored in the Encrypted Session Key packet(s).</t>
d message. <t>If the encryption container is preceded by one or more Symmetric Key
The message is encrypted with a session key, and the session key is itself encry Encrypted Session Key packets, each specifies a passphrase that may be used to d
pted and stored in the Encrypted Session Key packet(s).</t> ecrypt the message.
<t>If the encryption container is preceded by one or more Symmetric-Key Encrypte
d Session Key packets, each specifies a passphrase that may be used to decrypt t
he message.
This allows a message to be encrypted to a number of public keys, and also to on e or more passphrases.</t> This allows a message to be encrypted to a number of public keys, and also to on e or more passphrases.</t>
<t>The body of this packet starts with a 1-octet number giving the versi
<t>The body of this packet starts with a one-octet number giving the version num on number of the packet type.
ber of the packet type.
The currently defined versions are 4 and 6. The currently defined versions are 4 and 6.
The remainder of the packet depends on the version.</t> The remainder of the packet depends on the version.</t>
<t>The versions differ in how they encrypt the session key with the pass
<t>The versions differ in how they encrypt the session key with the passphrase, phrase and in what they encode.
and in what they encode.
The version of the SKESK packet must align with the version of the SEIPD packet (see <xref target="encrypted-message-versions"/>). The version of the SKESK packet must align with the version of the SEIPD packet (see <xref target="encrypted-message-versions"/>).
Any new version of the SKESK packet should be registered in the registry establi shed in <xref target="encrypted-message-versions"/>.</t> Any new version of the SKESK packet should be registered in the registry establi shed in <xref target="encrypted-message-versions"/>.</t>
<section anchor="v4-skesk">
<section anchor="v4-skesk"><name>Version 4 Symmetric-Key Encrypted Session Key P <name>Version 4 Symmetric Key Encrypted Session Key Packet Format</nam
acket Format</name> e>
<t>A v4 SKESK packet precedes a v1 SEIPD (see <xref target="version-on
<t>A version 4 Symmetric-Key Encrypted Session Key (SKESK) packet precedes a ver e-seipd"/>).
sion 1 Symmetrically Encrypted Integrity Protected Data (v1 SEIPD, see <xref tar In historic data, it is sometimes found preceding a deprecated SED packet (see <
get="version-one-seipd"/>) packet. xref target="sed"/>). A v4 SKESK packet <bcp14>MUST NOT</bcp14> precede a v2 SEI
In historic data, it is sometimes found preceding a deprecated Symmetrically Enc PD packet (see <xref target="encrypted-message-versions"/>).</t>
rypted Data packet (SED, see <xref target="sed"/>). <t>A version 4 Symmetric Key Encrypted Session Key packet consists of:
A v4 SKESK packet <bcp14>MUST NOT</bcp14> precede a v2 SEIPD packet (see <xref t </t>
arget="encrypted-message-versions"/>).</t> <ul spacing="normal">
<li>
<t>A version 4 Symmetric-Key Encrypted Session Key packet consists of:</t> <t>A 1-octet version number with value 4.</t>
</li>
<t><list style="symbols"> <li>
<t>A one-octet version number with value 4.</t> <t>A 1-octet number describing the symmetric algorithm used.</t>
<t>A one-octet number describing the symmetric algorithm used.</t> </li>
<t>A string-to-key (S2K) specifier. <li>
The length of the string-to-key specifier depends on its type (see <xref target= <t>An S2K Specifier. The length of the S2K Specifier depends on it
"s2k-types"/>).</t> s type (see <xref target="s2k-types"/>).</t>
<t>Optionally, the encrypted session key itself, which is decrypted with the s </li>
tring-to-key object.</t> <li>
</list></t> <t>Optionally, the encrypted session key itself, which is decrypte
d with the S2K object.</t>
<t>If the encrypted session key is not present (which can be detected on the bas </li>
is of packet length and S2K specifier size), then the S2K algorithm applied to t </ul>
he passphrase produces the session key for decrypting the message, using the sym <t>If the encrypted session key is not present (which can be detected
metric cipher algorithm from the Symmetric-Key Encrypted Session Key packet.</t> on the basis of packet length and S2K Specifier size), then the S2K algorithm ap
plied to the passphrase produces the session key for decrypting the message, usi
<t>If the encrypted session key is present, the result of applying the S2K algor ng the Symmetric Cipher Algorithm ID from the Symmetric Key Encrypted Session Ke
ithm to the passphrase is used to decrypt just that encrypted session key field, y packet.</t>
using CFB mode with an IV of all zeros. <t>If the encrypted session key is present, the result of applying the
The decryption result consists of a one-octet algorithm identifier that specifie S2K algorithm to the passphrase is used to decrypt just that encrypted session
s the symmetric-key encryption algorithm used to encrypt the following encryptio key field, using CFB mode with an IV of all zeros.
n container, followed by the session key octets themselves.</t> The decryption result consists of a 1-octet algorithm identifier that specifies
the symmetric key encryption algorithm used to encrypt the following encryption
<t>Note: because an all-zero IV is used for this decryption, the S2K specifier < container, followed by the session key octets themselves.</t>
bcp14>MUST</bcp14> use a salt value, either a Salted S2K, an Iterated-Salted S2K <t>Note: because an all-zero IV is used for this decryption, the S2K S
, or Argon2. pecifier <bcp14>MUST</bcp14> use a salt value, a Salted S2K, an Iterated and Sal
ted S2K, or Argon2.
The salt value will ensure that the decryption key is not repeated even if the p assphrase is reused.</t> The salt value will ensure that the decryption key is not repeated even if the p assphrase is reused.</t>
</section>
</section> <section anchor="v6-skesk">
<section anchor="v6-skesk"><name>Version 6 Symmetric-Key Encrypted Session Key P <name>Version 6 Symmetric Key Encrypted Session Key Packet Format</nam
acket Format</name> e>
<t>A v6 SKESK packet precedes a v2 SEIPD packet (see <xref target="ver
<t>A version 6 Symmetric-Key Encrypted Session Key (SKESK) packet precedes a ver sion-two-seipd"/>).
sion 2 Symmetrically Encrypted Integrity Protected Data (v2 SEIPD, see <xref tar
get="version-two-seipd"/>) packet.
A v6 SKESK packet <bcp14>MUST NOT</bcp14> precede a v1 SEIPD packet or a depreca ted Symmetrically Encrypted Data packet (see <xref target="encrypted-message-ver sions"/>).</t> A v6 SKESK packet <bcp14>MUST NOT</bcp14> precede a v1 SEIPD packet or a depreca ted Symmetrically Encrypted Data packet (see <xref target="encrypted-message-ver sions"/>).</t>
<t>A version 6 Symmetric Key Encrypted Session Key packet consists of:
<t>A version 6 Symmetric-Key Encrypted Session Key packet consists of:</t> </t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>A one-octet version number with value 6.</t> <t>A 1-octet version number with value 6.</t>
<t>A one-octet scalar octet count for the 5 fields following this octet.</t> </li>
<t>A one-octet symmetric cipher algorithm ID from <xref target="symkey-algorit <li>
hms-registry"/>.</t> <t>A 1-octet scalar octet count for the 5 fields following this oc
<t>A one-octet AEAD algorithm identifier from <xref target="aead-algorithms-re tet.</t>
gistry"/>.</t> </li>
<t>A one-octet scalar octet count of the following field.</t> <li>
<t>A string-to-key (S2K) specifier. <t>A 1-octet Symmetric Cipher Algorithm ID (from <xref target="sym
The length of the string-to-key specifier depends on its type (see <xref target= key-algorithms-registry"/>).</t>
"s2k-types"/>).</t> </li>
<t>A starting initialization vector of size specified by the AEAD algorithm.</ <li>
t> <t>A 1-octet AEAD algorithm identifier (from <xref target="aead-al
<t>The encrypted session key itself.</t> gorithms-registry"/>).</t>
<t>An authentication tag for the AEAD mode.</t> </li>
</list></t> <li>
<t>A 1-octet scalar octet count of the following field.</t>
<t>A key-encryption key is derived using HKDF (<xref target="RFC5869"/>) with SH </li>
A256 (<xref target="RFC6234"/>) as the hash algorithm. <li>
<t>An S2K Specifier. The length of the S2K Specifier depends on it
s type (see <xref target="s2k-types"/>).</t>
</li>
<li>
<t>A starting IV of the size specified by the AEAD algorithm.</t>
</li>
<li>
<t>The encrypted session key itself.</t>
</li>
<li>
<t>An authentication tag for the AEAD mode.</t>
</li>
</ul>
<t>A key-encryption key (KEK) is derived using HKDF <xref target="RFC5
869"/> with SHA256 <xref target="RFC6234"/> as the hash algorithm.
The Initial Keying Material (IKM) for HKDF is the key derived from S2K. The Initial Keying Material (IKM) for HKDF is the key derived from S2K.
No salt is used. No salt is used. The info parameter is comprised of the Packet Type ID in OpenPG
The info parameter is comprised of the Packet Type ID in OpenPGP format encoding P format encoding (bits 7 and 6 are set, and bits 5-0 carry the Packet Type ID),
(bits 7 and 6 set, bits 5-0 carry the packet type ID), the packet version, and the packet version, and the cipher-algo and AEAD-mode used to encrypt the key m
the cipher-algo and AEAD-mode used to encrypt the key material.</t> aterial.</t>
<t>Then, the session key is encrypted using the resulting key, with th
<t>Then, the session key is encrypted using the resulting key, with the AEAD alg e AEAD algorithm specified for the version 2 Symmetrically Encrypted and Integri
orithm specified for version 2 of the Symmetrically Encrypted Integrity Protecte ty Protected Data packet.
d Data packet.
Note that no chunks are used and that there is only one authentication tag. Note that no chunks are used and that there is only one authentication tag.
The Packet Type ID encoded in OpenPGP format (bits 7 and 6 set, bits 5-0 carry t he packet type ID), the packet version number, the cipher algorithm ID, and the AEAD algorithm ID are given as additional data. The Packet Type ID encoded in OpenPGP format (bits 7 and 6 are set, and bits 5-0 carry the Packet Type ID), the packet version number, the cipher algorithm ID, and the AEAD algorithm ID are given as additional data.
For example, the additional data used with AES-128 with OCB consists of the octe ts 0xC3, 0x06, 0x07, and 0x02.</t> For example, the additional data used with AES-128 with OCB consists of the octe ts 0xC3, 0x06, 0x07, and 0x02.</t>
</section>
</section> </section>
</section> <section anchor="one-pass-sig">
<section anchor="one-pass-sig"><name>One-Pass Signature Packet (Type ID 4)</name <name>One-Pass Signature Packet (Type ID 4)</name>
> <t>The One-Pass Signature packet precedes the signed data and contains e
nough information to allow the receiver to begin calculating any hashes needed t
<t>The One-Pass Signature packet precedes the signed data and contains enough in o verify the signature.
formation to allow the receiver to begin calculating any hashes needed to verify It allows the Signature packet to be placed at the end of the message so that th
the signature. e signer can compute the entire signed message in one pass.</t>
It allows the Signature packet to be placed at the end of the message, so that t <t>The body of this packet consists of:</t>
he signer can compute the entire signed message in one pass.</t> <ul spacing="normal">
<li>
<t>The body of this packet consists of:</t> <t>A 1-octet version number.
<t><list style="symbols">
<t>A one-octet version number.
The currently defined versions are 3 and 6. The currently defined versions are 3 and 6.
Any new One-Pass Signature packet version should be registered in the registry e stablished in <xref target="signed-message-versions"/>.</t> Any new One-Pass Signature packet version should be registered in the registry e stablished in <xref target="signed-message-versions"/>.</t>
<t>A one-octet signature type ID. </li>
<li>
<t>A 1-octet Signature Type ID.
Signature types are described in <xref target="signature-types"/>.</t> Signature types are described in <xref target="signature-types"/>.</t>
<t>A one-octet number describing the hash algorithm used.</t> </li>
<t>A one-octet number describing the public-key algorithm used.</t> <li>
<t>Only for v6 packets, a variable-length field containing: <list style="symb <t>A 1-octet number describing the hash algorithm used.</t>
ols"> </li>
<t>A one-octet salt size. The value <bcp14>MUST</bcp14> match the value de <li>
fined for the hash algorithm as specified in <xref target="hash-algorithms-regis <t>A 1-octet number describing the public key algorithm used.</t>
try"/>.</t> </li>
<t>The salt; a random value of the specified size. The value <bcp14>MUST</ <li>
bcp14> match the salt field of the corresponding Signature packet.</t> <t>Only for version 6 packets, a variable-length field containing:
</list></t> </t>
<t>Only for v3 packets, an eight-octet number holding the Key ID of the signin <ul spacing="normal">
g key.</t> <li>
<t>Only for v6 packets, 32 octets of the fingerprint of the signing key. <t>A 1-octet salt size. The value <bcp14>MUST</bcp14> match the
Since a v6 signature can only be made by a v6 key, the length of the fingerprint value defined for the hash algorithm as specified in <xref target="hash-algorith
is fixed.</t> ms-registry"/>.</t>
<t>A one-octet number holding a flag showing whether the signature is nested. </li>
<li>
<t>The salt; a random value of the specified size. The value <bc
p14>MUST</bcp14> match the salt field of the corresponding Signature packet.</t>
</li>
</ul>
</li>
<li>
<t>Only for v3 packets, an 8-octet number holding the Key ID of the
signing key.</t>
</li>
<li>
<t>Only for version 6 packets, 32 octets of the fingerprint of the s
igning key.
Since a version 6 signature can only be made by a version 6 key, the length of t
he fingerprint is fixed.</t>
</li>
<li>
<t>A 1-octet number holding a flag showing whether the signature is
nested.
A zero value indicates that the next packet is another One-Pass Signature packet that describes another signature to be applied to the same message data.</t> A zero value indicates that the next packet is another One-Pass Signature packet that describes another signature to be applied to the same message data.</t>
</list></t> </li>
</ul>
<t>When generating a one-pass signature, the OPS packet version <bcp14>MUST</bcp <t>When generating a one-pass signature, the OPS packet version <bcp14>M
14> correspond to the version of the associated signature packet, except for the UST</bcp14> correspond to the version of the associated Signature packet, except
historical accident that v4 keys use a v3 one-pass signature packet (there is n for the historical accident that version 4 keys use a version 3 One-Pass Signat
o v4 OPS). ure packet (there is no version 4 OPS).
See <xref target="signed-message-versions"/> for the full correspondence of vers ions between Keys, Signatures, and One-Pass Signatures.</t> See <xref target="signed-message-versions"/> for the full correspondence of vers ions between Keys, Signatures, and One-Pass Signatures.</t>
<t>Note that if a message contains more than one one-pass signature, the
<t>Note that if a message contains more than one one-pass signature, then the Si n the Signature packets bracket the message; that is, the first Signature packet
gnature packets bracket the message; that is, the first Signature packet after t after the message corresponds to the last One-Pass Signature packet and the fin
he message corresponds to the last one-pass packet and the final Signature packe al Signature packet corresponds to the first One-Pass Signature packet.</t>
t corresponds to the first one-pass packet.</t> </section>
<section anchor="key-material-packets">
</section> <name>Key Material Packets</name>
<section anchor="key-material-packets"><name>Key Material Packets</name> <t>A key material packet contains all the information about a public or
private key.
<t>A key material packet contains all the information about a public or private There are four variants of this packet type: two major versions (versions 4 and
key. 6) and two strongly deprecated versions (versions 2 and 3). Consequently, this s
There are four variants of this packet type, two major versions (versions 4 and ection is complex.</t>
6), and two strongly deprecated versions (versions 2 and 3). <t>For historical reasons, versions 1 and 5 of the key packets are unspe
Consequently, this section is complex.</t> cified.</t>
<section anchor="key-packet-variants">
<t>For historical reasons, versions 1 and 5 of the key packets are unspecified.< <name>Key Packet Variants</name>
/t> <section anchor="pubkey">
<name>Public Key Packet (Type ID 6)</name>
<section anchor="key-packet-variants"><name>Key Packet Variants</name> <t>A Public Key packet starts a series of packets that forms an Open
PGP Key (sometimes called an OpenPGP certificate).</t>
<section anchor="pubkey"><name>Public-Key Packet (Type ID 6)</name> </section>
<section anchor="pubsubkey">
<t>A Public-Key packet starts a series of packets that forms an OpenPGP key (som <name>Public Subkey Packet (Type ID 14)</name>
etimes called an OpenPGP certificate).</t> <t>A Public Subkey packet (Type ID 14) has exactly the same format a
s a Public Key packet, but it denotes a subkey. One or more subkeys may be assoc
</section> iated with a top-level key.
<section anchor="pubsubkey"><name>Public-Subkey Packet (Type ID 14)</name> By convention, the top-level key offers certification capability, but it does no
t provide encryption services, while a dedicated subkey provides encryption (see
<t>A Public-Subkey packet (type ID 14) has exactly the same format as a Public-K <xref target="common-requirements"/>).</t>
ey packet, but denotes a subkey. </section>
One or more subkeys may be associated with a top-level key. <section anchor="seckey">
By convention, the top-level key offers certification capability, but does not p <name>Secret Key Packet (Type ID 5)</name>
rovide encryption services, while a dedicated subkey provides encryption (see <x <t>A Secret Key packet contains all the information that is found in
ref target="common-requirements"/>).</t> a Public Key packet, including the public key material, but it also includes th
e secret key material after all the public key fields.</t>
</section> </section>
<section anchor="seckey"><name>Secret-Key Packet (Type ID 5)</name> <section anchor="secsubkey">
<name>Secret Subkey Packet (Type ID 7)</name>
<t>A Secret-Key packet contains all the information that is found in a Public-Ke <t>A Secret Subkey packet (Type ID 7) is the subkey analog of the Se
y packet, including the public-key material, but also includes the secret-key ma cret Key packet and has exactly the same format.</t>
terial after all the public-key fields.</t> </section>
</section>
</section> <section anchor="public-key-packet-formats">
<section anchor="secsubkey"><name>Secret-Subkey Packet (Type ID 7)</name> <name>Public Key Packet Formats</name>
<t>There are four versions of key material packets.
<t>A Secret-Subkey packet (type ID 7) is the subkey analog of the Secret-Key pac Versions 2 and 3 have been deprecated since 1998. Version 4 has been deprecated
ket and has exactly the same format.</t> by this document.</t>
<t>OpenPGP implementations <bcp14>SHOULD</bcp14> create keys with vers
</section> ion 6 format.
</section> Version 4 keys are deprecated; an implementation <bcp14>SHOULD NOT</bcp14> gener
<section anchor="public-key-packet-formats"><name>Public-Key Packet Formats</nam ate a version 4 key but <bcp14>SHOULD</bcp14> accept it. Version 3 keys are depr
e> ecated; an implementation <bcp14>MUST NOT</bcp14> generate a version 3 key but <
bcp14>MAY</bcp14> accept it. Version 2 keys are deprecated; an implementation <b
<t>There are four versions of key-material packets. cp14>MUST NOT</bcp14> generate a version 2 key but <bcp14>MAY</bcp14> accept it.
The V2 and V3 versions have been deprecated since 1998. </t>
The V4 version has been deprecated by this document in 2023.</t> <t>Any new Key Version must be registered in the registry established
in <xref target="signed-message-versions"/>.</t>
<t>OpenPGP implementations <bcp14>SHOULD</bcp14> create keys with version 6 form <section anchor="v3-pubkeys">
at. <name>Version 3 Public Keys</name>
V4 keys are deprecated; an implementation <bcp14>SHOULD NOT</bcp14> generate a v <t>Version 2 keys are identical to version 3 keys except for the ver
4 key, but <bcp14>SHOULD</bcp14> accept it. sion number.
V3 keys are deprecated; an implementation <bcp14>MUST NOT</bcp14> generate a v3 A version 3 Public Key or Public Subkey packet contains:</t>
key, but <bcp14>MAY</bcp14> accept it. <ul spacing="normal">
V2 keys are deprecated; an implementation <bcp14>MUST NOT</bcp14> generate a v2 <li>
key, but <bcp14>MAY</bcp14> accept it.</t> <t>A 1-octet version number (3).</t>
</li>
<t>Any new Key version must be registered in the registry established in <xref t <li>
arget="signed-message-versions"/>.</t> <t>A 4-octet number denoting the time that the key was created.<
/t>
<section anchor="v3-pubkeys"><name>Version 3 Public Keys</name> </li>
<li>
<t>V2 keys are identical to v3 keys except for the version number. <t>A 2-octet number denoting the time in days that the key is va
A version 3 public key or public-subkey packet contains:</t> lid.
<t><list style="symbols">
<t>A one-octet version number (3).</t>
<t>A four-octet number denoting the time that the key was created.</t>
<t>A two-octet number denoting the time in days that this key is valid.
If this number is zero, then it does not expire.</t> If this number is zero, then it does not expire.</t>
<t>A one-octet number denoting the public-key algorithm of this key.</t> </li>
<t>A series of multiprecision integers comprising the key material: <list sty <li>
le="symbols"> <t>A 1-octet number denoting the public key algorithm of the key
<t>A multiprecision integer (MPI) of RSA public modulus n;</t> .</t>
<t>An MPI of RSA public encryption exponent e.</t> </li>
</list></t> <li>
</list></t> <t>A series of multiprecision integers comprising the key materi
al: </t>
<t>V3 keys are deprecated. <ul spacing="normal">
They contain three weaknesses. <li>
First, it is relatively easy to construct a v3 key that has the same Key ID as a <t>MPI of RSA public modulus n.</t>
ny other key because the Key ID is simply the low 64 bits of the public modulus. </li>
Secondly, because the fingerprint of a v3 key hashes the key material, but not i <li>
ts length, there is an increased opportunity for fingerprint collisions. <t>MPI of RSA public encryption exponent e.</t>
Third, there are weaknesses in the MD5 hash algorithm that make developers prefe </li>
r other algorithms. </ul>
</li>
</ul>
<t>Version 3 keys are deprecated. They contain three weaknesses.
First, it is relatively easy to construct a version 3 key that has the same Key
ID as any other key because the Key ID is simply the low 64 bits of the public m
odulus.
Second, because the fingerprint of a version 3 key hashes the key material, but
not its length, there is an increased opportunity for fingerprint collisions.
Third, there are weaknesses in the MD5 hash algorithm that cause developers to p
refer other algorithms.
See <xref target="key-ids-fingerprints"/> for a fuller discussion of Key IDs and fingerprints.</t> See <xref target="key-ids-fingerprints"/> for a fuller discussion of Key IDs and fingerprints.</t>
</section>
</section> <section anchor="v4-pubkeys">
<section anchor="v4-pubkeys"><name>Version 4 Public Keys</name> <name>Version 4 Public Keys</name>
<t>The version 4 format is similar to the version 3 format except fo
<t>The version 4 format is similar to the version 3 format except for the absenc r the absence of a validity period.
e of a validity period.
This has been moved to the Signature packet. This has been moved to the Signature packet.
In addition, fingerprints of version 4 keys are calculated differently from vers ion 3 keys, as described in <xref target="key-ids-fingerprints"/>.</t> In addition, fingerprints of version 4 keys are calculated differently from vers ion 3 keys, as described in <xref target="key-ids-fingerprints"/>.</t>
<t>A version 4 packet contains:</t>
<ul spacing="normal">
<li>
<t>A 1-octet version number (4).</t>
</li>
<li>
<t>A 4-octet number denoting the time that the key was created.<
/t>
</li>
<li>
<t>A 1-octet number denoting the public key algorithm of the key
.</t>
</li>
<li>
<t>A series of values comprising the key material.
This is algorithm specific and described in <xref target="algorithm-specific-par
ts-of-keys"/>.</t>
</li>
</ul>
</section>
<section anchor="v6-pubkeys">
<name>Version 6 Public Keys</name>
<t>The version 6 format is similar to the version 4 format except fo
r the addition of a count for the key material.
This count helps parsing Secret Key packets (which are an extension of the Publi
c Key packet format) in the case of an unknown algorithm.
In addition, fingerprints of version 6 keys are calculated differentl
y from version 4 keys, as described in <xref target="key-ids-fingerprints"/>.</t
>
<t>A version 4 packet contains:</t> <t>A version 6 packet contains:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>A one-octet version number (4).</t> <t>A 1-octet version number (6).</t>
<t>A four-octet number denoting the time that the key was created.</t> </li>
<t>A one-octet number denoting the public-key algorithm of this key.</t> <li>
<t>A series of values comprising the key material. <t>A 4-octet number denoting the time that the key was created.<
This is algorithm-specific and described in <xref target="algorithm-specific-par /t>
ts-of-keys"/>.</t> </li>
</list></t> <li>
<t>A 1-octet number denoting the public key algorithm of the key
</section> .</t>
<section anchor="v6-pubkeys"><name>Version 6 Public Keys</name> </li>
<li>
<t>The version 6 format is similar to the version 4 format except for the additi <t>A 4-octet scalar octet count for the public key material spec
on of a count for the key material. ified in the next field.</t>
This count helps parsing secret key packets (which are an extension of the publi </li>
c key packet format) in the case of an unknown algorithm. <li>
In addition, fingerprints of version 6 keys are calculated differently from vers <t>A series of values comprising the public key material.
ion 4 keys, as described in <xref target="key-ids-fingerprints"/>.</t> This is algorithm specific and described in <xref target="algorithm-specific-par
ts-of-keys"/>.</t>
<t>A version 6 packet contains:</t> </li>
</ul>
<t><list style="symbols"> </section>
<t>A one-octet version number (6).</t> </section>
<t>A four-octet number denoting the time that the key was created.</t> <section anchor="secret-key-packet-formats">
<t>A one-octet number denoting the public-key algorithm of this key.</t> <name>Secret Key Packet Formats</name>
<t>A four-octet scalar octet count for the following public key material.</t> <t>The Secret Key and Secret Subkey packets contain all the data of th
<t>A series of values comprising the public key material. e Public Key and Public Subkey packets, with additional algorithm-specific secre
This is algorithm-specific and described in <xref target="algorithm-specific-par t key data appended, usually in encrypted form.</t>
ts-of-keys"/>.</t> <t>The packet contains:</t>
</list></t> <ul spacing="normal">
<li>
</section> <t>The fields of a Public Key or Public Subkey packet, as describe
</section> d above.</t>
<section anchor="secret-key-packet-formats"><name>Secret-Key Packet Formats</nam </li>
e> <li>
<t>One octet (the "S2K usage octet") indicating whether and how th
<t>The Secret-Key and Secret-Subkey packets contain all the data of the Public-K e secret key material is protected by a passphrase.
ey and Public-Subkey packets, with additional algorithm-specific secret-key data Zero indicates that the secret key data is not encrypted. 253 (AEAD), 254 (CFB)
appended, usually in encrypted form.</t> , or 255 (MalleableCFB) indicates that an S2K Specifier and other parameters wil
l follow.
<t>The packet contains:</t> Any other value is a symmetric key encryption algorithm identifier.
<t><list style="symbols">
<t>The fields of a Public-Key or Public-Subkey packet, as described above.</t>
<t>One octet (the "S2K usage octet") indicating whether and how the secret key
material is protected by a passphrase.
Zero indicates that the secret-key data is not encrypted.
255 (MalleableCFB), 254 (CFB), or 253 (AEAD) indicates that a string-to-key spec
ifier and other parameters will follow.
Any other value is a symmetric-key encryption algorithm identifier.
A version 6 packet <bcp14>MUST NOT</bcp14> use the value 255 (MalleableCFB).</t> A version 6 packet <bcp14>MUST NOT</bcp14> use the value 255 (MalleableCFB).</t>
<t>Only for a version 6 packet where the secret key material is encrypted (tha </li>
t is, where the previous octet is not zero), a one-octet scalar octet count of t <li>
he cumulative length of all the following conditionally included string-to-key p <t>Only for a version 6 packet where the secret key material is en
arameter fields.</t> crypted (that is, where the previous octet is not zero), a 1-octet scalar octet
<t>Conditionally included string-to-key parameter fields: <list style="symbol count of the cumulative length of all the following conditionally included S2K p
s"> arameter fields.</t>
<t>If string-to-key usage octet was 255, 254, or 253, a one-octet symmetri </li>
c encryption algorithm.</t> <li>
<t>If string-to-key usage octet was 253 (AEAD), a one-octet AEAD algorithm <t>Conditionally included S2K parameter fields: </t>
.</t> <ul spacing="normal">
<t>Only for a version 6 packet, and if string-to-key usage octet was 254, <li>
or 253, a one-octet count of the size of the one field following this octet.</t> <t>If the S2K usage octet was 253, 254, or 255, a 1-octet symm
<t>If string-to-key usage octet was 255, 254, or 253, a string-to-key (S2K etric key encryption algorithm.</t>
) specifier. </li>
The length of the string-to-key specifier depends on its type (see <xref target= <li>
"s2k-types"/>).</t> <t>If the S2K usage octet was 253 (AEAD), a 1-octet AEAD algor
<t>If string-to-key usage octet was 253 (AEAD), an initialization vector ( ithm.</t>
IV) of size specified by the AEAD algorithm (see <xref target="version-two-seipd </li>
"/>), which is used as the nonce for the AEAD algorithm.</t> <li>
<t>If string-to-key usage octet was 255, 254, or a cipher algorithm ID (th <t>Only for a version 6 packet, and if the S2K usage octet was
at is, the secret data uses some form of CFB encryption), an initialization vect 253 or 254, a 1-octet count of the size of the one field following this octet.<
or (IV) of the same length as the cipher's block size.</t> /t>
</list></t> </li>
<t>Plain or encrypted multiprecision integers comprising the secret key data. <li>
This is algorithm-specific and described in <xref target="algorithm-specific-par <t>If the S2K usage octet was 253, 254, or 255, an S2K Specifi
ts-of-keys"/>. er. The length of the S2K Specifier depends on its type (see <xref target="s2k-t
If the string-to-key usage octet is 253 (AEAD), then an AEAD authentication tag ypes"/>).</t>
is at the end of that data. </li>
If the string-to-key usage octet is 254 (CFB), a 20-octet SHA-1 hash of the plai <li>
ntext of the algorithm-specific portion is appended to plaintext and encrypted w <t>If the S2K usage octet was 253 (AEAD), an IV of a size spec
ith it. ified by the AEAD algorithm (see <xref target="version-two-seipd"/>), which is u
If the string-to-key usage octet is 255 (MalleableCFB) or another nonzero value sed as the nonce for the AEAD algorithm.</t>
(that is, a symmetric-key encryption algorithm identifier), a two-octet checksum </li>
of the plaintext of the algorithm-specific portion (sum of all octets, mod 6553 <li>
6) is appended to plaintext and encrypted with it. <t>If the S2K usage octet was 254, 255, or a cipher algorithm
(This is deprecated and <bcp14>SHOULD NOT</bcp14> be used, see below.)</t> ID (that is, the secret data uses some form of CFB encryption), an IV of the sam
<t>Only for a version 3 or 4 packet where the string-to-key usage octet is zer e length as the cipher's block size.</t>
o, a two-octet checksum of the algorithm-specific portion (sum of all octets, mo </li>
d 65536).</t> </ul>
</list></t> </li>
<li>
<t>The details about storing algorithm-specific secrets above are summarized in <t>Plain or encrypted multiprecision integers comprising the secre
<xref target="secret-key-protection-registry"/>.</t> t key data.
This is algorithm specific and described in <xref target="algorithm-specific-par
<t>Note that the version 6 packet format adds two count values to help parsing p ts-of-keys"/>.
ackets with unknown S2K or public key algorithms.</t> If the S2K usage octet is 253 (AEAD), then an AEAD authentication tag is at the
end of that data.
<t>Secret MPI values can be encrypted using a passphrase. If the S2K usage octet is 254 (CFB), a 20-octet SHA-1 hash of the plaintext of t
If a string-to-key specifier is given, that describes the algorithm for converti he algorithm-specific portion is appended to plaintext and encrypted with it.
ng the passphrase to a key, else a simple MD5 hash of the passphrase is used. If the S2K usage octet is 255 (MalleableCFB) or another non-zero value (that is,
An implementation producing a passphrase-protected secret key packet <bcp14>MUST a symmetric key encryption algorithm identifier), a 2-octet checksum of the pla
</bcp14> use a string-to-key specifier; the simple hash is for read-only backwar intext of the algorithm-specific portion (sum of all octets, mod 65536) is appen
d compatibility, though implementations <bcp14>MAY</bcp14> continue to use exist ded to plaintext and encrypted with it.
ing private keys in the old format. (This is deprecated and <bcp14>SHOULD NOT</bcp14> be used; see below.)</t>
The cipher for encrypting the MPIs is specified in the Secret-Key packet.</t> </li>
<li>
<t>Encryption/decryption of the secret data is done using the key created from t <t>Only for a version 3 or 4 packet where the S2K usage octet is z
he passphrase and the initialization vector from the packet. ero, a 2-octet checksum of the algorithm-specific portion (sum of all octets, mo
If the string-to-key usage octet is not 253, CFB mode is used. d 65536).</t>
A different mode is used with v3 keys (which are only RSA) than with other key f </li>
ormats. </ul>
With v3 keys, the MPI bit count prefix (that is, the first two octets) is not en <t>The details about storing algorithm-specific secrets above are summ
crypted. arized in <xref target="secret-key-protection-registry"/>.</t>
<t>Note that the version 6 packet format adds two count values to help
parsing packets with unknown S2K or public key algorithms.</t>
<t>Secret MPI values can be encrypted using a passphrase. If an S2K Sp
ecifier is given, it describes the algorithm for converting the passphrase to a
key; otherwise, a simple MD5 hash of the passphrase is used. An implementation p
roducing a passphrase-protected Secret Key packet <bcp14>MUST</bcp14> use an S2K
Specifier; the simple hash is for read-only backward compatibility, though impl
ementations <bcp14>MAY</bcp14> continue to use existing private keys in the old
format. The cipher for encrypting the MPIs is specified in the Secret Key packet
.</t>
<t>Encryption/decryption of the secret data is done using the key crea
ted from the passphrase and the IV from the packet.
If the S2K usage octet is not 253, CFB mode is used.
A different mode is used with version 3 keys (which are only RSA) than with othe
r key formats.
With version 3 keys, the MPI bit count prefix (that is, the first two octets) is
not encrypted.
Only the MPI non-prefix data is encrypted. Only the MPI non-prefix data is encrypted.
Furthermore, the CFB state is resynchronized at the beginning of each new MPI va Furthermore, the CFB state is resynchronized at the beginning of each new MPI va
lue, so that the CFB block boundary is aligned with the start of the MPI data.</ lue so that the CFB block boundary is aligned with the start of the MPI data.</t
t> >
<t>With version 4 and version 6 keys, a simpler method is used.
<t>With v4 and v6 keys, a simpler method is used. All secret MPI values are encrypted, including the MPI bit count prefix.</t>
All secret MPI values are encrypted, including the MPI bitcount prefix.</t> <t>If the S2K usage octet is 253, the KEK is derived using HKDF <xref
target="RFC5869"/> to provide key separation. SHA256 <xref target="RFC6234"/> is
<t>If the string-to-key usage octet is 253, the key encryption key is derived us used as the hash algorithm for HKDF. IKM for HKDF is the key derived from S2K.
ing HKDF (<xref target="RFC5869"/>) to provide key separation. No salt is used. The info parameter is comprised of the Packet Type ID
SHA256 (<xref target="RFC6234"/>) is used as the hash algorithm for HKDF. encoded in OpenPGP format (bits 7 and 6 are set, and bits 5-0 carry the Packet T
The Initial Keying Material (IKM) for HKDF is the key derived from S2K. ype ID), the packet version, and the cipher-algo and AEAD-mode used to encrypt t
No salt is used. he key material.</t>
The info parameter is comprised of the Packet Type ID encoded in OpenPGP format <t>Then, the encrypted MPI values are encrypted as one combined plaint
(bits 7 and 6 set, bits 5-0 carry the packet type ID), the packet version, and t ext using one of the AEAD algorithms specified for the version 2 Symmetrically E
he cipher-algo and AEAD-mode used to encrypt the key material.</t> ncrypted and Integrity Protected Data packet.
<t>Then, the encrypted MPI values are encrypted as one combined plaintext using
one of the AEAD algorithms specified for version 2 of the Symmetrically Encrypte
d Integrity Protected Data packet.
Note that no chunks are used and that there is only one authentication tag. Note that no chunks are used and that there is only one authentication tag.
As additional data, the Packet Type ID in OpenPGP format encoding (bits 7 and 6 As additional data, the Packet Type ID in OpenPGP format encoding (bits 7 and 6
set, bits 5-0 carry the packet type ID), followed by the public key packet field are set, and bits 5-0 carry the Packet Type ID), followed by the Public Key pack
s, starting with the packet version number, are passed to the AEAD algorithm. et fields, starting with the packet version number, are passed to the AEAD algor
For example, the additional data used with a Secret-Key packet of version 4 cons ithm. For example, the additional data used with a Secret Key packet of version
ists of the octets 0xC5, 0x04, followed by four octets of creation time, one oct 4 consists of the octets 0xC5, 0x04, followed by four octets of creation time, o
et denoting the public-key algorithm, and the algorithm-specific public-key para ne octet denoting the public key algorithm, and the algorithm-specific public ke
meters. y parameters.
For a Secret-Subkey packet, the first octet would be 0xC7. For a Secret Subkey packet, the first octet would be 0xC7.
For a version 6 key packet, the second octet would be 0x06, and the four-octet o For a version 6 key packet, the second octet would be 0x06, and the 4-octet octe
ctet count of the public key material would be included as well (see <xref targe t count of the public key material would be included as well (see <xref target="
t="public-key-packet-formats"/>).</t> public-key-packet-formats"/>).</t>
<t>The 2-octet checksum that follows the algorithm-specific portion is
<t>The two-octet checksum that follows the algorithm-specific portion is the alg the algebraic sum, mod 65536, of the plaintext of all the algorithm-specific oc
ebraic sum, mod 65536, of the plaintext of all the algorithm-specific octets (in tets (including the MPI prefix and data).
cluding MPI prefix and data). With version 3 keys, the checksum is stored in the clear. With version 4 keys, t
With v3 keys, the checksum is stored in the clear. he checksum is encrypted like the algorithm-specific data. This value is used to
With v4 keys, the checksum is encrypted like the algorithm-specific data. check that the passphrase was correct.
This value is used to check that the passphrase was correct. However, this checksum is deprecated, and an implementation <bcp14>SHOULD NOT</b
However, this checksum is deprecated; an implementation <bcp14>SHOULD NOT</bcp14 cp14> use it; instead, an implementation should use the SHA-1 hash denoted with
> use it, but should rather use the SHA-1 hash denoted with a usage octet of 254 a usage octet of 254.
. The reason for this is that there are some attacks that involve modifying the se
The reason for this is that there are some attacks that involve undetectably mod cret key undetected.
ifying the secret key. If the S2K usage octet is 253, no checksum or SHA-1 hash is used, but the authen
If the string-to-key usage octet is 253 no checksum or SHA-1 hash is used but th tication tag of the AEAD algorithm follows.</t>
e authentication tag of the AEAD algorithm follows.</t> <t>When decrypting the secret key material using any of these schemes
(that is, where the usage octet is non-zero), the resulting cleartext octet stre
<t>When decrypting the secret key material using any of these schemes (that is, am must be well formed.
where the usage octet is non-zero), the resulting cleartext octet stream must be
well-formed.
In particular, an implementation <bcp14>MUST NOT</bcp14> interpret octets beyond the unwrapped cleartext octet stream as part of any of the unwrapped MPI object s. In particular, an implementation <bcp14>MUST NOT</bcp14> interpret octets beyond the unwrapped cleartext octet stream as part of any of the unwrapped MPI object s.
Furthermore, an implementation <bcp14>MUST</bcp14> reject as unusable any secret Furthermore, an implementation <bcp14>MUST</bcp14> reject any secret key materia
key material whose cleartext length does not align with the lengths of the unwr l whose cleartext length does not align with the lengths of the unwrapped MPI ob
apped MPI objects.</t> jects as unusable.</t>
</section>
</section> <section anchor="key-ids-fingerprints">
<section anchor="key-ids-fingerprints"><name>Key IDs and Fingerprints</name> <name>Key IDs and Fingerprints</name>
<t>Every OpenPGP Key has a fingerprint and a Key ID.
<t>Every OpenPGP key has a fingerprint and a key ID.
The computation of these values differs based on the key version. The computation of these values differs based on the key version.
The fingerprint length varies with the key version, but the key ID (which is onl y used in v3 PKESK packets, see <xref target="v3-pkesk"/>) is always 64 bits. The fingerprint length varies with the key version, but the Key ID (which is onl y used in v3 PKESK packets; see <xref target="v3-pkesk"/>) is always 64 bits.
The following registry represents the subsections below:</t> The following registry represents the subsections below:</t>
<texttable title="OpenPGP Key ID and Fingerprint registry" anchor="key-id-finger <table anchor="key-id-fingerprint-registry">
print-registry"> <name>OpenPGP Key IDs and Fingerprints Registry</name>
<ttcol align='left'>Key Version</ttcol> <thead>
<ttcol align='left'>Fingerprint</ttcol> <tr>
<ttcol align='left'>Fingerprint Length (bits)</ttcol> <th align="left">Key Version</th>
<ttcol align='left'>Key ID</ttcol> <th align="left">Fingerprint</th>
<ttcol align='left'>Reference</ttcol> <th align="left">Fingerprint Length (Bits)</th>
<c>3</c> <th align="left">Key ID</th>
<c>MD5(MPIs without length octets)</c> <th align="left">Reference</th>
<c>128</c> </tr>
<c>low 64 bits of RSA modulus</c> </thead>
<c><xref target="v3-key-id-fingerprint"/></c> <tbody>
<c>4</c> <tr>
<c>SHA1(normalized pubkey packet)</c> <td align="left">3</td>
<c>160</c> <td align="left">MD5(MPIs without length octets)</td>
<c>last 64 bits of fingerprint</c> <td align="left">128</td>
<c><xref target="v4-key-id-fingerprint"/></c> <td align="left">low 64 bits of RSA modulus</td>
<c>6</c> <td align="left">
<c>SHA256(normalized pubkey packet)</c> <xref target="v3-key-id-fingerprint"/></td>
<c>256</c> </tr>
<c>first 64 bits of fingerprint</c> <tr>
<c><xref target="v6-key-id-fingerprint"/></c> <td align="left">4</td>
</texttable> <td align="left">SHA1(normalized pubkey packet)</td>
<td align="left">160</td>
<section anchor="v3-key-id-fingerprint"><name>Version 3 Key ID and Fingerprint</ <td align="left">last 64 bits of fingerprint</td>
name> <td align="left">
<xref target="v4-key-id-fingerprint"/></td>
<t>For a v3 key, the eight-octet Key ID consists of the low 64 bits of the publi </tr>
c modulus of the RSA key.</t> <tr>
<td align="left">6</td>
<t>The fingerprint of a v3 key is formed by hashing the body (but not the two-oc <td align="left">SHA256(normalized pubkey packet)</td>
tet length) of the MPIs that form the key material (public modulus n, followed b <td align="left">256</td>
y exponent e) with MD5. <td align="left">first 64 bits of fingerprint</td>
Note that both v3 keys and MD5 are deprecated.</t> <td align="left">
<xref target="v6-key-id-fingerprint"/></td>
</section> </tr>
<section anchor="v4-key-id-fingerprint"><name>Version 4 Key ID and Fingerprint</ </tbody>
name> </table>
<section anchor="v3-key-id-fingerprint">
<t>A v4 fingerprint is the 160-bit SHA-1 hash of the octet 0x99, followed by the <name>Version 3 Key ID and Fingerprint</name>
two-octet packet length, followed by the entire Public-Key packet starting with <t>For a version 3 key, the 8-octet Key ID consists of the low 64 bi
the version field. ts of the public modulus of the RSA key.</t>
<t>The fingerprint of a version 3 key is formed by hashing the body
(but not the 2-octet length) of the MPIs that form the key material (public modu
lus n, followed by exponent e) with MD5.
Note that both version 3 keys and MD5 are deprecated.</t>
</section>
<section anchor="v4-key-id-fingerprint">
<name>Version 4 Key ID and Fingerprint</name>
<t>A version 4 fingerprint is the 160-bit SHA-1 hash of the octet 0x
99, followed by the 2-octet packet length, followed by the entire Public Key pac
ket starting with the version field.
The Key ID is the low-order 64 bits of the fingerprint. The Key ID is the low-order 64 bits of the fingerprint.
Here are the fields of the hash material, with the example of an Ed25519 key:</t Here are the fields of the hash material, including an example of an Ed25519 key
> :</t>
<ol type="a.%d)">
<t>a.1) 0x99 (1 octet)</t> <li>0x99 (1 octet)</li>
<li>2-octet, big-endian scalar octet count of (b)-(e)</li>
<t>a.2) two-octet, big-endian scalar octet count of (b)-(e)</t> </ol>
<ol type="%c)" start="2">
<t>b) version number = 4 (1 octet);</t> <li>version number = 4 (1 octet)</li>
<li>timestamp of key creation (4 octets)</li>
<t>c) timestamp of key creation (4 octets);</t> <li>algorithm (1 octet): 27 = Ed25519 (example)</li>
<li>algorithm-specific fields</li>
<t>d) algorithm (1 octet): 27 = Ed25519 (example);</t> </ol>
<t>Algorithm-specific fields for Ed25519 keys (example):</t>
<t>e) Algorithm-specific fields.</t>
<t>Algorithm-Specific Fields for Ed25519 keys (example):</t>
<t>e.1) 32 octets representing the public key.</t>
</section>
<section anchor="v6-key-id-fingerprint"><name>Version 6 Key ID and Fingerprint</
name>
<t>A v6 fingerprint is the 256-bit SHA2-256 hash of the octet 0x9B, followed by <ol type="e.%d)">
the four-octet packet length, followed by the entire Public-Key packet starting <li>32 octets representing the public key</li>
with the version field. </ol>
</section>
<section anchor="v6-key-id-fingerprint">
<name>Version 6 Key ID and Fingerprint</name>
<t>A version 6 fingerprint is the 256-bit SHA2-256 hash of the octet
0x9B, followed by the 4-octet packet length, followed by the entire Public Key
packet starting with the version field.
The Key ID is the high-order 64 bits of the fingerprint. The Key ID is the high-order 64 bits of the fingerprint.
Here are the fields of the hash material, with the example of an Ed25519 key:</t Here are the fields of the hash material, including an example of an
> Ed25519 key:</t>
<t>a.1) 0x9B (1 octet)</t>
<t>a.2) four-octet scalar octet count of (b)-(f)</t>
<t>b) version number = 6 (1 octet);</t>
<t>c) timestamp of key creation (4 octets);</t>
<t>d) algorithm (1 octet): 27 = Ed25519 (example);</t>
<t>e) four-octet scalar octet count for the following key material;</t>
<t>f) algorithm-specific fields.</t>
<t>Algorithm-Specific Fields for Ed25519 keys (example):</t>
<t>e.1) 32 octets representing the public key.</t>
<t>Note that it is possible for there to be collisions of Key IDs --- two differ
ent keys with the same Key ID.
Note that there is a much smaller, but still non-zero, probability that two diff
erent keys have the same fingerprint.</t>
<t>Also note that if v3, v4, and v6 format keys share the same RSA key material,
they will have different Key IDs as well as different fingerprints.</t>
<t>Finally, the Key ID and fingerprint of a subkey are calculated in the same wa
y as for a primary key, including the 0x99 (v4 key) or 0x9B (v6 key) as the firs
t octet (even though this is not a valid packet type ID for a public subkey).</t
>
</section> <ol type="a.%d)">
</section> <li>0x9B (1 octet)</li>
<section anchor="algorithm-specific-parts-of-keys"><name>Algorithm-specific Part <li>4-octet scalar octet count of (b)-(f)</li>
s of Keys</name> </ol>
<ol type="%c)" start="2">
<li>version number = 6 (1 octet)</li>
<li>timestamp of key creation (4 octets)</li>
<li>algorithm (1 octet): 27 = Ed25519 (example)</li>
<li>4-octet scalar octet count for the key material specified in the
next field</li>
<li>algorithm-specific public key material</li>
</ol>
<t>Algorithm-specific fields for Ed25519 keys (example):</t>
<t>The public and secret key format specifies algorithm-specific parts of a key. <ol type="f.%d)">
<li>32 octets representing the public key</li>
</ol>
<t>Note that it is possible for there to be collisions of Key IDs --
that is, two different keys with the same Key ID. Note that there is a much sma
ller, but still non-zero, probability that two different keys have the same fing
erprint.</t>
<t>Also note that if version 3, version 4, and version 6 format keys
share the same RSA key material, they will have different Key IDs as well as di
fferent fingerprints.</t>
<t>Finally, the Key ID and fingerprint of a subkey are calculated in
the same way as for a primary key, including the 0x99 (version 4 key) or 0x9B (
version 6 key) as the first octet (even though this is not a valid Packet Type I
D for a public subkey).</t>
</section>
</section>
<section anchor="algorithm-specific-parts-of-keys">
<name>Algorithm-Specific Parts of Keys</name>
<t>The public and secret key formats specify algorithm-specific parts
of a key.
The following sections describe them in detail.</t> The following sections describe them in detail.</t>
<section anchor="key-rsa">
<section anchor="key-rsa"><name>Algorithm-Specific Part for RSA Keys</name> <name>Algorithm-Specific Part for RSA Keys</name>
<t>For RSA keys, the public key consists of this series of multiprec
<t>The public key is this series of multiprecision integers:</t> ision integers:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>MPI of RSA public modulus n;</t> <t>MPI of RSA public modulus n,</t>
<t>MPI of RSA public encryption exponent e.</t> </li>
</list></t> <li>
<t>MPI of RSA public encryption exponent e.</t>
<t>The secret key is this series of multiprecision integers:</t> </li>
</ul>
<t><list style="symbols"> <t>The secret key consists of this series of multiprecision integers
<t>MPI of RSA secret exponent d;</t> :</t>
<t>MPI of RSA secret prime value p;</t> <ul spacing="normal">
<t>MPI of RSA secret prime value q (p &lt; q);</t> <li>
<t>MPI of u, the multiplicative inverse of p, mod q.</t> <t>MPI of RSA secret exponent d;</t>
</list></t> </li>
<li>
</section> <t>MPI of RSA secret prime value p;</t>
<section anchor="key-dsa"><name>Algorithm-Specific Part for DSA Keys</name> </li>
<li>
<t>The public key is this series of multiprecision integers:</t> <t>MPI of RSA secret prime value q (p &lt; q); and</t>
</li>
<t><list style="symbols"> <li>
<t>MPI of DSA prime p;</t> <t>MPI of u, the multiplicative inverse of p, mod q.</t>
<t>MPI of DSA group order q (q is a prime divisor of p-1);</t> </li>
<t>MPI of DSA group generator g;</t> </ul>
<t>MPI of DSA public-key value y (= g**x mod p where x is secret).</t> </section>
</list></t> <section anchor="key-dsa">
<name>Algorithm-Specific Part for DSA Keys</name>
<t>The secret key is this single multiprecision integer:</t> <t>For DSA keys, the public key consists of this series of multiprec
ision integers:</t>
<t><list style="symbols"> <ul spacing="normal">
<t>MPI of DSA secret exponent x.</t> <li>
</list></t> <t>MPI of DSA prime p;</t>
</li>
</section> <li>
<section anchor="key-elgamal"><name>Algorithm-Specific Part for Elgamal Keys</na <t>MPI of DSA group order q (q is a prime divisor of p-1);</t>
me> </li>
<li>
<t>The public key is this series of multiprecision integers:</t> <t>MPI of DSA group generator g; and</t>
</li>
<t><list style="symbols"> <li>
<t>MPI of Elgamal prime p;</t> <t>MPI of DSA public key value y (= g<sup>x</sup> mod p where x
<t>MPI of Elgamal group generator g;</t> is secret).</t>
<t>MPI of Elgamal public key value y (= g**x mod p where x is secret).</t> </li>
</list></t> </ul>
<t>The secret key consists of this single multiprecision integer:</t
<t>The secret key is this single multiprecision integer:</t> >
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>MPI of Elgamal secret exponent x.</t> <t>MPI of DSA secret exponent x.</t>
</list></t> </li>
</ul>
</section> </section>
<section anchor="key-ecdsa"><name>Algorithm-Specific Part for ECDSA Keys</name> <section anchor="key-elgamal">
<name>Algorithm-Specific Part for Elgamal Keys</name>
<t>The public key is this series of values:</t> <t>For Elgamal keys, the public key consists of this series of multi
precision integers:</t>
<t><list style="symbols"> <ul spacing="normal">
<t>A variable-length field containing a curve OID, which is formatted as follo <li>
ws: <list style="symbols"> <t>MPI of Elgamal prime p;</t>
<t>A one-octet size of the following field; values 0 and 0xFF are reserved </li>
for future extensions,</t> <li>
<t>The octets representing a curve OID (defined in <xref target="ec-curves <t>MPI of Elgamal group generator g; and</t>
"/>);</t> </li>
</list></t> <li>
<t>MPI of an EC point representing a public key.</t> <t>MPI of Elgamal public key value y (= g<sup>x</sup> mod p wher
</list></t> e x is secret).</t>
</li>
<t>The secret key is this single multiprecision integer:</t> </ul>
<t>The secret key consists of this single multiprecision integer:</t
<t><list style="symbols"> >
<t>MPI of an integer representing the secret key, which is a scalar of the pub <ul spacing="normal">
lic EC point.</t> <li>
</list></t> <t>MPI of Elgamal secret exponent x.</t>
</li>
</section> </ul>
<section anchor="key-eddsa-legacy"><name>Algorithm-Specific Part for EdDSALegacy </section>
Keys (deprecated)</name> <section anchor="key-ecdsa">
<name>Algorithm-Specific Part for ECDSA Keys</name>
<t>The public key is this series of values:</t> <t>For ECDSA keys, the public key consists of this series of values:
</t>
<t><list style="symbols"> <ul spacing="normal">
<t>A variable-length field containing a curve OID, formatted as follows: <lis <li>
t style="symbols"> <t>A variable-length field containing a curve OID, which is form
<t>A one-octet size of the following field; values 0 and 0xFF are reserved atted as follows: </t>
for future extensions,</t> <ul spacing="normal">
<t>The octets representing a curve OID, defined in <xref target="ec-curves <li>
"/>;</t> <t>A 1-octet size of the following field; values 0 and 0xFF
</list></t> are reserved for future extensions.</t>
<t>An MPI of an EC point representing a public key Q in prefixed native form ( </li>
see <xref target="ec-point-prefixed-native"/>).</t> <li>
</list></t> <t>The octets representing a curve OID, as defined in <xref
target="ec-curves"/>.</t>
<t>The secret key is this single multiprecision integer:</t> </li>
</ul>
<t><list style="symbols"> </li>
<t>An MPI-encoded octet string representing the native form of the secret key, <li>
in the curve-specific format described in <xref target="curve-specific-formats" <t>An MPI of an EC point representing a public key.</t>
/>.</t> </li>
</list></t> </ul>
<t>The secret key consists of this single multiprecision integer:</t
<t>Note that the native form for an EdDSA secret key is a fixed-width sequence o >
f unstructured random octets, with size corresponding to the specific curve. <ul spacing="normal">
That sequence of random octets is used with a cryptographic digest to produce bo <li>
th a curve-specific secret scalar and a prefix used when making a signature. <t>An MPI of an integer representing the secret key, which is a
scalar of the public EC point.</t>
</li>
</ul>
</section>
<section anchor="key-eddsa-legacy">
<name>Algorithm-Specific Part for EdDSALegacy Keys (Deprecated)</nam
e>
<t>For EdDSALegacy keys (deprecated), the public key consists of thi
s series of values:</t>
<ul spacing="normal">
<li>
<t>A variable-length field containing a curve OID, formatted as
follows: </t>
<ul spacing="normal">
<li>
<t>A 1-octet size of the following field; values 0 and 0xFF
are reserved for future extensions.</t>
</li>
<li>
<t>The octets representing a curve OID, as defined in <xref
target="ec-curves"/>.</t>
</li>
</ul>
</li>
<li>
<t>An MPI of an EC point representing a public key Q in prefixed
native form (see <xref target="ec-point-prefixed-native"/>).</t>
</li>
</ul>
<t>The secret key consists of this single multiprecision integer:</t
>
<ul spacing="normal">
<li>
<t>An MPI-encoded octet string representing the native form of t
he secret key in the curve-specific format, as described in <xref target="curve-
specific-formats"/>.</t>
</li>
</ul>
<t>Note that the native form for an EdDSA secret key is a fixed-widt
h sequence of unstructured random octets, with size corresponding to the specifi
c curve. That sequence of random octets is used with a cryptographic digest to p
roduce both a curve-specific secret scalar and a prefix used when making a signa
ture.
See <xref section="5.1.5" sectionFormat="of" target="RFC8032"/> for more details about how to use the native octet strings for Ed25519Legacy. See <xref section="5.1.5" sectionFormat="of" target="RFC8032"/> for more details about how to use the native octet strings for Ed25519Legacy.
The value stored in an OpenPGP EdDSALegacy secret key packet is the original seq The value stored in an OpenPGP EdDSALegacy Secret Key packet is the original seq
uence of random octets.</t> uence of random octets.</t>
<t>Note that the only curve defined for use with EdDSALegacy is the
<t>Note that the only curve defined for use with EdDSALegacy is the Ed25519Legac Ed25519Legacy OID.</t>
y OID.</t> </section>
<section anchor="key-ecdh">
</section> <name>Algorithm-Specific Part for ECDH Keys</name>
<section anchor="key-ecdh"><name>Algorithm-Specific Part for ECDH Keys</name> <t>For ECDH keys, the public key consists of this series of values:<
/t>
<t>The public key is this series of values:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>A variable-length field containing a curve OID, which is form
<t>A variable-length field containing a curve OID, which is formatted as follo atted as follows: </t>
ws: <list style="symbols"> <ul spacing="normal">
<t>A one-octet size of the following field; values 0 and 0xFF are reserved <li>
for future extensions,</t> <t>A 1-octet size of the following field; values 0 and 0xFF
<t>Octets representing a curve OID, defined in <xref target="ec-curves"/>; are reserved for future extensions.</t>
</t> </li>
</list></t> <li>
<t>MPI of an EC point representing a public key, in the point format associate <t>The octets representing a curve OID, as defined in <xref
d with the curve as specified in <xref target="curve-specific-formats"/>.</t> target="ec-curves"/>.</t>
<t>A variable-length field containing KDF parameters, which is formatted as fo </li>
llows: <list style="symbols"> </ul>
<t>A one-octet size of the following fields; values 0 and 0xFF are reserve </li>
d for future extensions,</t> <li>
<t>A one-octet value 1, reserved for future extensions,</t> <t>An MPI of an EC point representing a public key, in the point
<t>A one-octet hash function ID used with a KDF,</t> format associated with the curve, as specified in <xref target="curve-specific-
<t>A one-octet algorithm ID for the symmetric algorithm used to wrap the s formats"/>.</t>
ymmetric key used for the message encryption; see <xref target="ecdh"/> for deta </li>
ils.</t> <li>
</list></t> <t>A variable-length field containing key derivation function (K
</list></t> DF) parameters, which is formatted as follows: </t>
<ul spacing="normal">
<t>The secret key is this single multiprecision integer:</t> <li>
<t>A 1-octet size of the following fields; values 0 and 0xFF
<t><list style="symbols"> are reserved for future extensions.</t>
<t>An MPI representing the secret key, in the curve-specific format described </li>
in <xref target="curve-specific-formats"/>.</t> <li>
</list></t> <t>A 1-octet value 1, reserved for future extensions.</t>
</li>
<section anchor="ecdh-secret-key-material"><name>ECDH Secret Key Material</name> <li>
<t>A 1-octet hash function ID used with a KDF.</t>
<t>When curve NIST P-256, NIST P-384, NIST P-521, brainpoolP256r1, brainpoolP384 </li>
r1, or brainpoolP512r1 are used in ECDH, their secret keys are represented as a <li>
simple integer in standard MPI form. <t>A 1-octet algorithm ID for the symmetric algorithm that i
s used to wrap the symmetric key for message encryption; see <xref target="ecdh"
/> for details.</t>
</li>
</ul>
</li>
</ul>
<t>The secret key consists of this single multiprecision integer:</t
>
<ul spacing="normal">
<li>
<t>An MPI representing the secret key, in the curve-specific for
mat described in <xref target="curve-specific-formats"/>.</t>
</li>
</ul>
<section anchor="ecdh-secret-key-material">
<name>ECDH Secret Key Material</name>
<t>When curve NIST P-256, NIST P-384, NIST P-521, brainpoolP256r1,
brainpoolP384r1, or brainpoolP512r1 are used in ECDH, their secret keys are rep
resented as a simple integer in standard MPI form.
Other curves are presented on the wire differently (though still as a single MPI ), as described below and in <xref target="curve-specific-formats"/>.</t> Other curves are presented on the wire differently (though still as a single MPI ), as described below and in <xref target="curve-specific-formats"/>.</t>
<section anchor="curve25519-secrets">
<section anchor="curve25519-secrets"><name>Curve25519Legacy ECDH Secret Key Mate <name>Curve25519Legacy ECDH Secret Key Material (Deprecated)</na
rial (deprecated)</name> me>
<t>A Curve25519Legacy secret key is stored as a standard integer
<t>A Curve25519Legacy secret key is stored as a standard integer in big-endian M in big-endian MPI form.
PI form.
Curve25519Legacy <bcp14>MUST NOT</bcp14> be used in key packets version 6 or abo ve. Curve25519Legacy <bcp14>MUST NOT</bcp14> be used in key packets version 6 or abo ve.
Note that this form is in reverse octet order from the little-endian "native" fo rm found in <xref target="RFC7748"/>.</t> Note that this form is in reverse octet order from the little-endian "native" fo rm found in <xref target="RFC7748"/>.</t>
<t>Note also that the integer for a Curve25519Legacy secret key
<t>Note also that the integer for a Curve25519Legacy secret key for OpenPGP <bcp for OpenPGP <bcp14>MUST</bcp14> have the appropriate form; that is, it <bcp14>MU
14>MUST</bcp14> have the appropriate form: that is, it <bcp14>MUST</bcp14> be di ST</bcp14> be divisible by 8, <bcp14>MUST</bcp14> be at least 2<sup>254</sup>, a
visible by 8, <bcp14>MUST</bcp14> be at least 2**254, and <bcp14>MUST</bcp14> be nd <bcp14>MUST</bcp14> be less than 2<sup>255</sup>.
less than 2**255. The length of this MPI in bits is by definition always 255, so the two leading o
The length of this MPI in bits is by definition always 255, so the two leading o ctets of the MPI will always be <tt>00 FF</tt>, and reversing the following 32 o
ctets of the MPI will always be <spanx style="verb">00 FF</spanx> and reversing ctets from the wire will produce the "native" form.</t>
the following 32 octets from the wire will produce the "native" form.</t> <t>When generating a new Curve25519Legacy secret key from 32 ful
ly random octets, the following pseudocode produces the MPI wire format (note th
<t>When generating a new Curve25519Legacy secret key from 32 fully-random octets e similarity to <tt>decodeScalar25519</tt> as described in <xref target="RFC7748
, the following pseudocode produces the MPI wire format (note the similarity to "/>):</t>
<spanx style="verb">decodeScalar25519</spanx> from <xref target="RFC7748"/>):</t <sourcecode type="pseudocode"><![CDATA[
>
<figure><artwork><![CDATA[
def curve25519Legacy_MPI_from_random(octet_list): def curve25519Legacy_MPI_from_random(octet_list):
octet_list[0] &= 248 octet_list[0] &= 248
octet_list[31] &= 127 octet_list[31] &= 127
octet_list[31] |= 64 octet_list[31] |= 64
mpi_header = [ 0x00, 0xFF ] mpi_header = [ 0x00, 0xFF ]
return mpi_header || reversed(octet_list) return mpi_header || reversed(octet_list)
]]></artwork></figure> ]]></sourcecode>
</section>
</section> </section>
</section> </section>
</section> <section anchor="key-x25519">
<section anchor="key-x25519"><name>Algorithm-Specific Part for X25519 Keys</name <name>Algorithm-Specific Part for X25519 Keys</name>
> <t>For X25519 keys, the public key consists of this single value:</t
>
<t>The public key is this single value:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>32 octets of the native public key.</t>
<t>32 octets of the native public key.</t> </li>
</list></t> </ul>
<t>The secret key consists of this single value:</t>
<t>The secret key is this single value:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>32 octets of the native secret key.</t>
<t>32 octets of the native secret key.</t> </li>
</list></t> </ul>
<t>See <xref section="6.1" sectionFormat="of" target="RFC7748"/> for
<t>See <xref section="6.1" sectionFormat="of" target="RFC7748"/> for more detail more details about how to use the native octet strings.
s about how to use the native octet strings. The value stored in an OpenPGP X25519 Secret Key packet is the original sequence
The value stored in an OpenPGP X25519 secret key packet is the original sequence of random octets.
of random octets. The value stored in an OpenPGP X25519 Public Key packet is the value X25519(secr
The value stored in an OpenPGP X25519 public key packet is the value X25519(secr etKey, 9).</t>
etKey, 9).</t> </section>
<section anchor="key-x448">
</section> <name>Algorithm-Specific Part for X448 Keys</name>
<section anchor="key-x448"><name>Algorithm-Specific Part for X448 Keys</name> <t>For X448 keys, the public key consists of this single value:</t>
<ul spacing="normal">
<t>The public key is this single value:</t> <li>
<t>56 octets of the native public key.</t>
<t><list style="symbols"> </li>
<t>56 octets of the native public key.</t> </ul>
</list></t> <t>The secret key consists of this single value:</t>
<ul spacing="normal">
<t>The secret key is this single value:</t> <li>
<t>56 octets of the native secret key.</t>
<t><list style="symbols"> </li>
<t>56 octets of the native secret key.</t> </ul>
</list></t> <t>See <xref section="6.2" sectionFormat="of" target="RFC7748"/> for
more details about how to use the native octet strings.
<t>See <xref section="6.2" sectionFormat="of" target="RFC7748"/> for more detail The value stored in an OpenPGP X448 Secret Key packet is the original sequence o
s about how to use the native octet strings. f random octets.
The value stored in an OpenPGP X448 secret key packet is the original sequence o The value stored in an OpenPGP X448 Public Key packet is the value X448(secretKe
f random octets. y, 5).</t>
The value stored in an OpenPGP X448 public key packet is the value X448(secretKe </section>
y, 5).</t> <section anchor="key-ed25519">
<name>Algorithm-Specific Part for Ed25519 Keys</name>
</section> <t>For Ed25519 keys, the public key consists of this single value:</
<section anchor="key-ed25519"><name>Algorithm-Specific Part for Ed25519 Keys</na t>
me> <ul spacing="normal">
<li>
<t>The public key is this single value:</t> <t>32 octets of the native public key.</t>
</li>
<t><list style="symbols"> </ul>
<t>32 octets of the native public key.</t> <t>The secret key consists of this single value:</t>
</list></t> <ul spacing="normal">
<li>
<t>The secret key is this single value:</t> <t>32 octets of the native secret key.</t>
</li>
<t><list style="symbols"> </ul>
<t>32 octets of the native secret key.</t> <t>See <xref section="5.1.5" sectionFormat="of" target="RFC8032"/> f
</list></t> or more details about how to use the native octet strings.
The value stored in an OpenPGP Ed25519 Secret Key packet is the original sequenc
<t>See <xref section="5.1.5" sectionFormat="of" target="RFC8032"/> for more deta e of random octets.</t>
ils about how to use the native octet strings. </section>
The value stored in an OpenPGP Ed25519 secret key packet is the original sequenc <section anchor="key-ed448">
e of random octets.</t> <name>Algorithm-Specific Part for Ed448 Keys</name>
<t>For Ed448 keys, the public key consists of this single value:</t>
</section> <ul spacing="normal">
<section anchor="key-ed448"><name>Algorithm-Specific Part for Ed448 Keys</name> <li>
<t>57 octets of the native public key.</t>
<t>The public key is this single value:</t> </li>
</ul>
<t><list style="symbols"> <t>The secret key consists of this single value:</t>
<t>57 octets of the native public key.</t> <ul spacing="normal">
</list></t> <li>
<t>57 octets of the native secret key.</t>
<t>The secret key is this single value:</t> </li>
</ul>
<t><list style="symbols"> <t>See <xref section="5.2.5" sectionFormat="of" target="RFC8032"/> f
<t>57 octets of the native secret key.</t> or more details about how to use the native octet strings.
</list></t> The value stored in an OpenPGP Ed448 Secret Key packet is the original sequence
of random octets.</t>
<t>See <xref section="5.2.5" sectionFormat="of" target="RFC8032"/> for more deta </section>
ils about how to use the native octet strings. </section>
The value stored in an OpenPGP Ed448 secret key packet is the original sequence </section>
of random octets.</t> <section anchor="compressed-data">
<name>Compressed Data Packet (Type ID 8)</name>
</section> <t>The Compressed Data packet contains compressed data.
</section> Typically, this packet is found as the contents of an encrypted packet, or follo
</section> wing a Signature or One-Pass Signature packet, and contains a Literal Data packe
<section anchor="compressed-data"><name>Compressed Data Packet (Type ID 8)</name t.</t>
> <t>The body of this packet consists of:</t>
<ul spacing="normal">
<t>The Compressed Data packet contains compressed data. <li>
Typically, this packet is found as the contents of an encrypted packet, or follo <t>One octet specifying the algorithm used to compress the packet.</
wing a Signature or One-Pass Signature packet, and contains a literal data packe t>
t.</t> </li>
<li>
<t>The body of this packet consists of:</t> <t>Compressed data, which makes up the remainder of the packet.</t>
</li>
<t><list style="symbols"> </ul>
<t>One octet that gives the algorithm used to compress the packet.</t> <t>A Compressed Data packet's body contains data that is a compression o
<t>Compressed data, which makes up the remainder of the packet.</t> f a series of OpenPGP packets.
</list></t>
<t>A Compressed Data packet's body contains data that is a compression of a seri
es of OpenPGP packets.
See <xref target="packet-sequence-composition"/> for details on how messages are formed.</t> See <xref target="packet-sequence-composition"/> for details on how messages are formed.</t>
<t>A ZIP-compressed series of packets is compressed into raw DEFLATE blo
<t>A ZIP-compressed series of packets is compressed into raw <xref target="RFC19 cks <xref target="RFC1951"/>.</t>
51"/> DEFLATE blocks.</t> <t>A ZLIB-compressed series of packets is compressed with raw ZLIB-style
blocks <xref target="RFC1950"/>.</t>
<t>A ZLIB-compressed series of packets is compressed with raw <xref target="RFC1 <t>A BZip2-compressed series of packets is compressed using the BZip2 <x
950"/> ZLIB-style blocks.</t> ref target="BZ2"/> algorithm.</t>
<t>An implementation that generates a Compressed Data packet <bcp14>MUST
<t>A BZip2-compressed series of packets is compressed using the BZip2 <xref targ </bcp14> use the OpenPGP format for packet framing (see <xref target="openpgp-pa
et="BZ2"/> algorithm.</t> cket-format"/>).
It <bcp14>MUST NOT</bcp14> generate a Compressed Data packet with Legacy format
<t>An implementation that generates a Compressed Data packet <bcp14>MUST</bcp14> (<xref target="legacy-packet-format"/>).</t>
use the non-legacy format for packet framing (see <xref target="openpgp-packet- <t>An implementation that deals with either historic data or data genera
format"/>). ted by legacy implementations predating support for <xref target="RFC2440"/> <bc
It <bcp14>MUST NOT</bcp14> generate a Compressed Data packet with Legacy format p14>MAY</bcp14> interpret Compressed Data packets that use the Legacy format for
(<xref target="legacy-packet-format"/>)</t> packet framing.</t>
</section>
<t>An implementation that deals with either historic data or data generated by l <section anchor="sed">
egacy implementations predating support for <xref target="RFC2440"/> <bcp14>MAY< <name>Symmetrically Encrypted Data Packet (Type ID 9)</name>
/bcp14> interpret Compressed Data packets that use the Legacy format for packet <t>The Symmetrically Encrypted Data packet contains data encrypted with
framing.</t> a symmetric key algorithm. When it has been decrypted, it contains other packets
(usually a Literal Data packet or compressed data packet, but in theory, it cou
</section> ld be another sequence of packets that forms a valid OpenPGP Message).</t>
<section anchor="sed"><name>Symmetrically Encrypted Data Packet (Type ID 9)</nam <t>This packet is obsolete.
e>
<t>The Symmetrically Encrypted Data packet contains data encrypted with a symmet
ric-key algorithm.
When it has been decrypted, it contains other packets (usually a literal data pa
cket or compressed data packet, but in theory other Symmetrically Encrypted Data
packets or sequences of packets that form whole OpenPGP messages).</t>
<t>This packet is obsolete.
An implementation <bcp14>MUST NOT</bcp14> create this packet. An implementation <bcp14>MUST NOT</bcp14> create this packet.
An implementation <bcp14>SHOULD</bcp14> reject such a packet and stop processing the message. An implementation <bcp14>SHOULD</bcp14> reject such a packet and stop processing the message.
If an implementation chooses to process the packet anyway, it <bcp14>MUST</bcp14 If an implementation chooses to process the packet anyway, it <bcp14>MUST</bcp14
> return a clear warning that a non-integrity protected packet has been processe > return a clear warning that a non-integrity-protected packet has been processe
d.</t> d.</t>
<t>This packet format is impossible to handle safely in general because
<t>This packet format is impossible to handle safely in general because the ciph the ciphertext it provides is malleable.
ertext it provides is malleable.
See <xref target="ciphertext-malleability"/> about selecting a better OpenPGP en cryption container that does not have this flaw.</t> See <xref target="ciphertext-malleability"/> about selecting a better OpenPGP en cryption container that does not have this flaw.</t>
<t>The body of this packet consists of:</t>
<t>The body of this packet consists of:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>A random prefix, containing block-size random octets (for example
<t>A random prefix, containing block-size random octets (for example, 16 octet , 16 octets for a 128-bit block length) followed by a copy of the last two octet
s for a 128-bit block length) followed by a copy of the last two octets, encrypt s, encrypted together using Cipher Feedback (CFB) mode, with an IV of all zeros.
ed together using Cipher Feedback (CFB) mode, with an Initial Vector (IV) of all </t>
zeros.</t> </li>
<t>Data encrypted using CFB mode, with the last block-size octets of the first <li>
ciphertext as the IV.</t> <t>Data encrypted using CFB mode, with the last block-size octets of
</list></t> the first ciphertext as the IV.</t>
</li>
<t>The symmetric cipher used may be specified in a Public-Key or Symmetric-Key E </ul>
ncrypted Session Key packet that precedes the Symmetrically Encrypted Data packe <t>The symmetric cipher used may be specified in a Public Key or Symmetr
t. ic Key Encrypted Session Key packet that precedes the Symmetrically Encrypted Da
ta packet.
In that case, the cipher algorithm ID is prefixed to the session key before it i s encrypted. In that case, the cipher algorithm ID is prefixed to the session key before it i s encrypted.
If no packets of these types precede the encrypted data, the IDEA algorithm is u sed with the session key calculated as the MD5 hash of the passphrase, though th is use is deprecated.</t> If no packets of these types precede the encrypted data, the IDEA algorithm is u sed with the session key calculated as the MD5 hash of the passphrase, though th is use is deprecated.</t>
<t>The data is encrypted in CFB mode (see <xref target="cfb-mode"/>).
<t>The data is encrypted in CFB mode (see <xref target="cfb-mode"/>). For the random prefix, the IV is specified as all zeros. Instead of achieving ra
For the random prefix, the Initial Vector (IV) is specified as all zeros. ndomized encryption through an IV, a string of length equal to the block size of
Instead of achieving randomized encryption through an IV, a string of length equ the cipher plus two is encrypted for this purpose. The first block-size octets
al to the block size of the cipher plus two is encrypted for this purpose. (for example, 16 octets for a 128-bit block length) are random, and the followin
The first block-size octets (for example, 16 octets for a 128-bit block length) g two octets are copies of the last two octets of the first block-size random oc
are random, and the following two octets are copies of the last two octets of th tets. For example, for a 16-octet block length, octet 17 is a copy of octet 15,
e first block-size random octets. and octet 18 is a copy of octet 16. For a cipher of block length 8, octet 9 is a
For example, for a 16-octet block length, octet 17 is a copy of octet 15 and oct copy of octet 7, and octet 10 is a copy of octet 8. (In both of these examples,
et 18 is a copy of octet 16. we consider the first octet to be numbered 1.)</t>
For a cipher of block length 8, octet 9 is a copy of octet 7, and octet 10 is a <t>After encrypting these block-size-plus-two octets, a new CFB context
copy of octet 8. is created for the encryption of the data, with the last block-size octets of th
(In both these examples, we consider the first octet to be numbered 1.)</t> e first ciphertext as the IV. (Alternatively and equivalently, the CFB state is
resynchronized: the last block-size octets of ciphertext are passed through the
<t>After encrypting these block-size-plus-two octets, a new CFB context is creat cipher, and the block boundary is reset.)</t>
ed for the encryption of the data, with the last block-size octets of the first <t>The repetition of two octets in the random prefix allows the receiver
ciphertext as the IV. to immediately check whether the session key is incorrect.
(Alternatively and equivalently, the CFB state is resynchronized: the last block
-size octets of ciphertext are passed through the cipher and the block boundary
is reset.)</t>
<t>The repetition of two octets in the random prefix allows the receiver to imme
diately check whether the session key is incorrect.
See <xref target="quick-check-oracle"/> for hints on the proper use of this "qui ck check".</t> See <xref target="quick-check-oracle"/> for hints on the proper use of this "qui ck check".</t>
</section>
</section> <section anchor="marker-packet">
<section anchor="marker-packet"><name>Marker Packet (Type ID 10)</name> <name>Marker Packet (Type ID 10)</name>
<t>The body of the Marker packet consists of:</t>
<t>The body of this packet consists of:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>The three octets 0x50, 0x47, 0x50 (which spell "PGP" in UTF-8).</
<t>The three octets 0x50, 0x47, 0x50 (which spell "PGP" in UTF-8).</t> t>
</list></t> </li>
</ul>
<t>Such a packet <bcp14>MUST</bcp14> be ignored when received.</t> <t>Such a packet <bcp14>MUST</bcp14> be ignored when received.</t>
</section>
</section> <section anchor="lit">
<section anchor="lit"><name>Literal Data Packet (Type ID 11)</name> <name>Literal Data Packet (Type ID 11)</name>
<t>A Literal Data packet contains the body of a message; that is, data t
<t>A Literal Data packet contains the body of a message; data that is not to be hat is not to be further interpreted.</t>
further interpreted.</t> <t>The body of this packet consists of:</t>
<ul spacing="normal">
<t>The body of this packet consists of:</t> <li>
<t>A 1-octet field that describes how the data is formatted. </t>
<t><list style="symbols"> <t>
<t>A one-octet field that describes how the data is formatted. <vspace blankL If it is a <tt>b</tt> (0x62), then the Literal Data packet contains binary data.
ines='1'/> If it is a <tt>u</tt> (0x75), then the Literal Data packet contains UTF-8-encode
If it is a <spanx style="verb">b</spanx> (0x62), then the Literal packet contain d text data and thus may need line ends converted to local form or other text mo
s binary data. de changes. </t>
If it is a <spanx style="verb">u</spanx> (0x75), then the Literal packet contain <t>
s UTF-8-encoded text data, and thus may need line ends converted to local form, Previous versions of the OpenPGP specification used <tt>t</tt> (0x74) to indicat
or other text mode changes. <vspace blankLines='1'/> e textual data but did not specify the character encoding. Implementations <bcp1
Older versions of OpenPGP used <spanx style="verb">t</spanx> (0x74) to indicate 4>SHOULD NOT</bcp14> emit this value.
textual data, but did not specify the character encoding. An implementation that receives a Literal Data packet with this value in the for
Implementations <bcp14>SHOULD NOT</bcp14> emit this value. mat field <bcp14>SHOULD</bcp14> interpret the packet data as UTF-8 encoded text,
An implementation that receives a literal data packet with this value in the for unless reliable (not attacker-controlled) context indicates a specific alternat
mat field <bcp14>SHOULD</bcp14> interpret the packet data as UTF-8 encoded text, e text encoding. This mode is deprecated due to its ambiguity. </t>
unless reliable (not attacker-controlled) context indicates a specific alternat <t>
e text encoding. Some implementations predating <xref target="RFC2440"/> also defined a value of
This mode is deprecated due to its ambiguity. <vspace blankLines='1'/> <tt>l</tt> as a "local" mode for machine-local conversions. <xref target="RFC199
Some implementations predating <xref target="RFC2440"/> also defined a value of 1"/> incorrectly states that this local mode flag is <tt>1</tt> (ASCII numeral o
<spanx style="verb">l</spanx> as a 'local' mode for machine-local conversions. ne). Both of these local modes are deprecated.</t>
<xref target="RFC1991"/> incorrectly stated this local mode flag as <spanx style </li>
="verb">1</spanx> (ASCII numeral one). <li>
Both of these local modes are deprecated.</t> <t>The file name as a string (1-octet length, followed by a file nam
<t>File name as a string (one-octet length, followed by a file name). e).
This may be a zero-length string. This may be a zero-length string. Commonly, if the source of the encr
Commonly, if the source of the encrypted data is a file, this will be the name o ypted data is a file, it will be the name of the encrypted file. An implementati
f the encrypted file. on <bcp14>MAY</bcp14> consider the file name in the Literal Data packet to be a
An implementation <bcp14>MAY</bcp14> consider the file name in the Literal packe more authoritative name than the actual file name.</t>
t to be a more authoritative name than the actual file name.</t> </li>
<t>A four-octet number that indicates a date associated with the literal data. <li>
<t>A 4-octet number that indicates a date associated with the litera
l data.
Commonly, the date might be the modification date of a file, or the time the pac ket was created, or a zero that indicates no specific time.</t> Commonly, the date might be the modification date of a file, or the time the pac ket was created, or a zero that indicates no specific time.</t>
<t>The remainder of the packet is literal data. <vspace blankLines='1'/> </li>
<li>
<t>The remainder of the packet is literal data. </t>
<t>
Text data <bcp14>MUST</bcp14> be encoded with UTF-8 (see <xref target="RFC3629"/ >) and stored with &lt;CR&gt;&lt;LF&gt; text endings (that is, network-normal li ne endings). Text data <bcp14>MUST</bcp14> be encoded with UTF-8 (see <xref target="RFC3629"/ >) and stored with &lt;CR&gt;&lt;LF&gt; text endings (that is, network-normal li ne endings).
These should be converted to native line endings by the receiving implementation .</t> These should be converted to native line endings by the receiving implementation .</t>
</list></t> </li>
</ul>
<t>Note that OpenPGP signatures do not include the formatting octet, the file na <t>Note that OpenPGP signatures do not include the formatting octet, the
me, and the date field of the literal packet in a signature hash and thus those file name, and the date field of the Literal Data packet in a signature hash; t
fields are not protected against tampering in a signed document. herefore, those fields are not protected against tampering in a signed document.
A receiving implementation <bcp14>MUST NOT</bcp14> treat those fields as though A receiving implementation <bcp14>MUST NOT</bcp14> treat those fields as though
they were cryptographically secured by the surrounding signature either when rep they were cryptographically secured by the surrounding signature when either re
resenting them to the user or acting on them.</t> presenting them to the user or acting on them.</t>
<t>Due to their inherent malleability, an implementation that generates
<t>Due to their inherent malleability, an implementation that generates a litera a Literal Data packet <bcp14>SHOULD</bcp14> avoid storing any significant data i
l data packet <bcp14>SHOULD</bcp14> avoid storing any significant data in these n these fields.
fields. If the implementation is certain that the data is textual and is encoded with UT
If the implementation is certain that the data is textual and is encoded with UT F-8 (for example, if it will follow this Literal Data packet with a Signature pa
F-8 (for example, if it will follow this literal data packet with a signature pa cket of type 0x01 (see <xref target="signature-types"/>), it <bcp14>MAY</bcp14>
cket of type 0x01 (see <xref target="signature-types"/>), it <bcp14>MAY</bcp14> set the format octet to <tt>u</tt>.
set the format octet to <spanx style="verb">u</spanx>. Otherwise, it <bcp14>MUST</bcp14> set the format octet to <tt>b</tt>.
Otherwise, it <bcp14>MUST</bcp14> set the format octet to <spanx style="verb">b< It <bcp14>SHOULD</bcp14> set the filename to the empty string (encoded as a sing
/spanx>. le zero octet) and the timestamp to zero (encoded as four zero octets).</t>
It <bcp14>SHOULD</bcp14> set the filename to the empty string (encoded as a sing <t>An application that wishes to include such filesystem metadata within
le zero octet), and the timestamp to zero (encoded as four zero octets).</t> a signature is advised to sign an encapsulated archive (for example, <xref targ
et="PAX"/>).</t>
<t>An application that wishes to include such filesystem metadata within a signa <t>An implementation that generates a Literal Data packet <bcp14>MUST</b
ture is advised to sign an encapsulated archive (for example, <xref target="PAX" cp14> use the OpenPGP format for packet framing (see <xref target="openpgp-packe
/>).</t> t-format"/>).
It <bcp14>MUST NOT</bcp14> generate a Literal Data packet with Legacy format (<x
<t>An implementation that generates a Literal Data packet <bcp14>MUST</bcp14> us ref target="legacy-packet-format"/>).</t>
e the OpenPGP format for packet framing (see <xref target="openpgp-packet-format <t>An implementation that deals with either historic data or data genera
"/>). ted by an implementation that predates support for <xref target="RFC2440"/> <bcp
It <bcp14>MUST NOT</bcp14> generate a Literal Data packet with Legacy format (<x 14>MAY</bcp14> interpret Literal Data packets that use the Legacy format for pac
ref target="legacy-packet-format"/>)</t> ket framing.</t>
<section anchor="for-eyes-only">
<t>An implementation that deals with either historic data or data generated by a <name>Special Filename _CONSOLE (Deprecated)</name>
n implementation that predates support for <xref target="RFC2440"/> <bcp14>MAY</ <t>The Literal Data packet's filename field has a historical special c
bcp14> interpret Literal Data packets that use the Legacy format for packet fram ase for the special name <tt>_CONSOLE</tt>.
ing.</t> When the filename field is <tt>_CONSOLE</tt>, the message is considered to be "f
or your eyes only".
<section anchor="for-eyes-only"><name>Special Filename _CONSOLE (Deprecated)</na
me>
<t>The Literal Data packet's filename field has a historical special case for th
e special name <spanx style="verb">_CONSOLE</spanx>.
When the filename field is <spanx style="verb">_CONSOLE</spanx>, the message is
considered to be "for your eyes only".
This advises that the message data is unusually sensitive, and the receiving pro gram should process it more carefully, perhaps avoiding storing the received dat a to disk, for example.</t> This advises that the message data is unusually sensitive, and the receiving pro gram should process it more carefully, perhaps avoiding storing the received dat a to disk, for example.</t>
<t>An OpenPGP deployment that generates Literal Data packets <bcp14>MU
<t>An OpenPGP deployment that generates literal data packets <bcp14>MUST NOT</bc ST NOT</bcp14> depend on this indicator being honored in any particular way.
p14> depend on this indicator being honored in any particular way.
It cannot be enforced, and the field itself is not covered by any cryptographic signature.</t> It cannot be enforced, and the field itself is not covered by any cryptographic signature.</t>
<t>It is <bcp14>NOT RECOMMENDED</bcp14> to use this special filename i
<t>It is <bcp14>NOT RECOMMENDED</bcp14> to use this special filename in a newly- n a newly generated Literal Data packet.</t>
generated literal data packet.</t> </section>
</section>
</section> <section anchor="trust">
</section> <name>Trust Packet (Type ID 12)</name>
<section anchor="trust"><name>Trust Packet (Type ID 12)</name> <t>The Trust packet is used only within keyrings and is not normally exp
orted.
<t>The Trust packet is used only within keyrings and is not normally exported.
Trust packets contain data that record the user's specifications of which keyhol ders are trustworthy introducers, along with other information that implementati on uses for trust information. Trust packets contain data that record the user's specifications of which keyhol ders are trustworthy introducers, along with other information that implementati on uses for trust information.
The format of Trust packets is defined by a given implementation.</t> The format of Trust packets is defined by a given implementation.</t>
<t>Trust packets <bcp14>SHOULD NOT</bcp14> be emitted to output streams
<t>Trust packets <bcp14>SHOULD NOT</bcp14> be emitted to output streams that are that are transferred to other users, and they <bcp14>SHOULD</bcp14> be ignored o
transferred to other users, and they <bcp14>SHOULD</bcp14> be ignored on any in n any input other than local keyring files.</t>
put other than local keyring files.</t> </section>
<section anchor="uid">
</section> <name>User ID Packet (Type ID 13)</name>
<section anchor="uid"><name>User ID Packet (Type ID 13)</name> <t>A User ID packet consists of UTF-8 text that is intended to represent
the name and email address of the keyholder.
<t>A User ID packet consists of UTF-8 text that is intended to represent the nam By convention, it includes a mail name-addr as described in <xref target="RFC282
e and email address of the keyholder. 2"/>, but there are no restrictions on its content. The packet length in the hea
By convention, it includes an <xref target="RFC2822"/> mail name-addr, but there der specifies the length of the User ID.</t>
are no restrictions on its content. </section>
The packet length in the header specifies the length of the User ID.</t> <section anchor="user-attribute-packet">
<name>User Attribute Packet (Type ID 17)</name>
</section> <t>The User Attribute packet is a variation of the User ID packet.
<section anchor="user-attribute-packet"><name>User Attribute Packet (Type ID 17)
</name>
<t>The User Attribute packet is a variation of the User ID packet.
It is capable of storing more types of data than the User ID packet, which is li mited to text. It is capable of storing more types of data than the User ID packet, which is li mited to text.
Like the User ID packet, a User Attribute packet may be certified by the key own er ("self-signed") or any other key owner who cares to certify it. Like the User ID packet, a User Attribute packet may be certified by the key own er ("self-signed") or any other key owner who cares to certify it.
Except as noted, a User Attribute packet may be used anywhere that a User ID pac ket may be used.</t> Except as noted, a User Attribute packet may be used anywhere that a User ID pac ket may be used.</t>
<t>While User Attribute packets are not a required part of the OpenPGP s
<t>While User Attribute packets are not a required part of the OpenPGP standard, pecification, implementations <bcp14>SHOULD</bcp14> provide at least enough comp
implementations <bcp14>SHOULD</bcp14> provide at least enough compatibility to atibility to properly handle a certification signature on the User Attribute pac
properly handle a certification signature on the User Attribute packet. ket.
A simple way to do this is by treating the User Attribute packet as a User ID pa cket with opaque contents, but an implementation may use any method desired.</t> A simple way to do this is by treating the User Attribute packet as a User ID pa cket with opaque contents, but an implementation may use any method desired.</t>
<t>The User Attribute packet is made up of one or more attribute subpack
<t>The User Attribute packet is made up of one or more attribute subpackets. ets.
Each subpacket consists of a subpacket header and a body. Each subpacket consists of a subpacket header and a body.
The header consists of:</t> The header consists of:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>The subpacket length (1, 2, or 5 octets)</t> <t>the subpacket length (1, 2, or 5 octets)</t>
<t>The subpacket type ID (1 octet)</t> </li>
</list></t> <li>
<t>the Subpacket Type ID (1 octet)</t>
<t>and is followed by the subpacket specific data.</t> </li>
</ul>
<t>The following table lists the currently known subpackets:</t> <t>and is followed by the subpacket specific data.</t>
<t>The following table lists the currently known subpackets:</t>
<texttable title="OpenPGP User Attribute Subpacket Types registry" anchor="user- <table anchor="user-attr-subpacket-types-registry">
attr-subpacket-types-registry"> <name>OpenPGP User Attribute Subpacket Types Registry</name>
<ttcol align='right'>ID</ttcol> <thead>
<ttcol align='left'>Attribute Subpacket</ttcol> <tr>
<ttcol align='left'>Reference</ttcol> <th align="right">ID</th>
<c>1</c> <th align="left">Attribute Subpacket</th>
<c>Image Attribute Subpacket</c> <th align="left">Reference</th>
<c><xref target="uat-image"/></c> </tr>
<c>100-110</c> </thead>
<c>Private/Experimental Use</c> <tbody>
<c>&#160;</c> <tr>
</texttable> <td align="right">0</td>
<td align="left">Reserved</td>
<t>An implementation <bcp14>SHOULD</bcp14> ignore any subpacket of a type that i <td align="left"></td>
t does not recognize.</t> </tr>
<tr>
<section anchor="uat-image"><name>The Image Attribute Subpacket</name> <td align="right">1</td>
<td align="left">Image Attribute Subpacket</td>
<t>The Image Attribute subpacket is used to encode an image, presumably (but not <td align="left"><xref target="uat-image"/></td>
required to be) that of the key owner.</t> </tr>
<tr>
<t>The Image Attribute subpacket begins with an image header. <td align="right">100-110</td>
<td align="left">Private or Experimental Use</td>
<td align="left"></td>
</tr>
</tbody>
</table>
<t>An implementation <bcp14>SHOULD</bcp14> ignore any subpacket of a typ
e that it does not recognize.</t>
<section anchor="uat-image">
<name>Image Attribute Subpacket</name>
<t>The Image Attribute subpacket is used to encode an image, presumabl
y (but not required to be) that of the key owner.</t>
<t>The Image Attribute subpacket begins with an image header.
The first two octets of the image header contain the length of the image header. The first two octets of the image header contain the length of the image header.
Note that unlike other multi-octet numerical values in this document, due to a h Note that unlike other multi-octet numerical values in this document, due to a h
istorical accident this value is encoded as a little-endian number. istorical accident, this value is encoded as a little-endian number. The image h
The image header length is followed by a single octet for the image header versi eader length is followed by a single octet for the image header version.
on.
The only currently defined version of the image header is 1, which is a 16-octet image header. The only currently defined version of the image header is 1, which is a 16-octet image header.
The first three octets of a version 1 image header are thus 0x10, 0x00, 0x01.</t > The first three octets of a version 1 image header are thus 0x10, 0x00, 0x01.</t >
<table anchor="image-attribute-version-registry">
<texttable title="OpenPGP Image Attribute Version registry" anchor="image-attrib <name>OpenPGP Image Attribute Versions Registry</name>
ute-version-registry"> <thead>
<ttcol align='right'>Version</ttcol> <tr>
<ttcol align='left'>Reference</ttcol> <th align="right">Version</th>
<c>1</c> <th align="left">Reference</th>
<c><xref target="uat-image"/></c> </tr>
</texttable> </thead>
<tbody>
<t>The fourth octet of a version 1 image header designates the encoding format o <tr>
f the image. <td align="right">1</td>
<td align="left">
<xref target="uat-image"/></td>
</tr>
</tbody>
</table>
<t>The fourth octet of a version 1 image header designates the encodin
g format of the image.
The only currently defined encoding format is the value 1 to indicate JPEG. The only currently defined encoding format is the value 1 to indicate JPEG.
Image format IDs 100 through 110 are reserved for private or experimental use. Image format IDs 100 through 110 are reserved for Private or Experimental Use.
The rest of the version 1 image header is made up of 12 reserved octets, all of which <bcp14>MUST</bcp14> be set to 0.</t> The rest of the version 1 image header is made up of 12 reserved octets, all of which <bcp14>MUST</bcp14> be set to 0.</t>
<table anchor="image-attr-encoding-format-registry">
<name>OpenPGP Image Attribute Encoding Format Registry</name>
<thead>
<tr>
<th align="right">ID</th>
<th align="left">Encoding</th>
<texttable title="OpenPGP Image Attribute Encoding Format registry" anchor="imag </tr>
e-attr-encoding-format-registry"> </thead>
<ttcol align='right'>ID</ttcol> <tbody>
<ttcol align='left'>Encoding</ttcol> <tr>
<ttcol align='left'>Reference</ttcol> <td align="right">0</td>
<c>1</c> <td align="left">Reserved</td>
<c>JPEG</c>
<c>JPEG File Interchange Format (<xref target="JFIF"/>)</c>
<c>100-110</c>
<c>Private/Experimental use</c>
<c>&#160;</c>
</texttable>
<t>The rest of the image subpacket contains the image itself.
As the only currently defined image type is JPEG, the image is encoded in the JP
EG File Interchange Format (JFIF), a standard file format for JPEG images <xref
target="JFIF"/>.</t>
<t>An implementation <bcp14>MAY</bcp14> try to determine the type of an image by </tr>
examination of the image data if it is unable to handle a particular version of <tr>
the image header or if a specified encoding format value is not recognized.</t> <td align="right">1</td>
<td align="left">JPEG <xref target="JFIF"/></td>
</section> </tr>
</section> <tr>
<section anchor="seipd"><name>Symmetrically Encrypted Integrity Protected Data P <td align="right">100-110</td>
acket (Type ID 18)</name> <td align="left">Private or Experimental Use</td>
<t>This packet (the "SEIPD" packet) contains integrity protected and encrypted d </tr>
ata. </tbody>
</table>
<t>The rest of the image subpacket contains the image itself.
As the only currently defined image type is JPEG, the image is encoded in the JP
EG File Interchange Format (JFIF), a standard file format for JPEG images <xref
target="JFIF"/>.</t>
<t>An implementation <bcp14>MAY</bcp14> try to determine the type of a
n image by examination of the image data if it is unable to handle a particular
version of the image header or if a specified encoding format value is not recog
nized.</t>
</section>
</section>
<section anchor="seipd">
<name>Symmetrically Encrypted and Integrity Protected Data Packet (Type
ID 18)</name>
<t>The SEIPD packet contains integrity-protected and encrypted data.
When it has been decrypted, it will contain other packets forming an OpenPGP Mes sage (see <xref target="openpgp-messages"/>).</t> When it has been decrypted, it will contain other packets forming an OpenPGP Mes sage (see <xref target="openpgp-messages"/>).</t>
<t>The first octet of this packet is always used to indicate the version
<t>The first octet of this packet is always used to indicate the version number, number, but different versions contain ciphertext that is structured differentl
but different versions contain differently-structured ciphertext. y. Version 1 of this packet contains data encrypted with a symmetric key algorit
Version 1 of this packet contains data encrypted with a symmetric-key algorithm hm and is thus protected against modification by the SHA-1 hash algorithm. This
and protected against modification by the SHA-1 hash algorithm. mechanism was introduced in <xref target="RFC4880"/> and offers some protections
This mechanism was introduced in <xref target="RFC4880"/> and offers some protec against ciphertext malleability.</t>
tions against ciphertext malleability.</t> <t>Version 2 of this packet contains data encrypted with an AEAD constru
ction.
<t>Version 2 of this packet contains data encrypted with an authenticated encryp
tion and additional data (AEAD) construction.
This offers a more cryptographically rigorous defense against ciphertext malleab ility. This offers a more cryptographically rigorous defense against ciphertext malleab ility.
See <xref target="ciphertext-malleability"/> for more details on choosing betwee n these formats.</t> See <xref target="ciphertext-malleability"/> for more details on choosing betwee n these formats.</t>
<t>Any new version of the SEIPD packet should be registered in the regis
<t>Any new version of the SEIPD packet should be registered in the registry esta try established in <xref target="encrypted-message-versions"/>.</t>
blished in <xref target="encrypted-message-versions"/>.</t> <section anchor="version-one-seipd">
<name>Version 1 Symmetrically Encrypted and Integrity Protected Data P
<section anchor="version-one-seipd"><name>Version 1 Symmetrically Encrypted Inte acket Format</name>
grity Protected Data Packet Format</name> <t>A version 1 Symmetrically Encrypted and Integrity Protected Data pa
cket consists of:</t>
<t>A version 1 Symmetrically Encrypted Integrity Protected Data packet consists <ul spacing="normal">
of:</t> <li>
<t>A 1-octet version number with value 1.</t>
<t><list style="symbols"> </li>
<t>A one-octet version number with value 1.</t> <li>
<t>Encrypted data, the output of the selected symmetric-key cipher operating i <t>Encrypted data -- the output of the selected symmetric key ciph
n Cipher Feedback (CFB) mode.</t> er operating in CFB mode.</t>
</list></t> </li>
</ul>
<t>The symmetric cipher used <bcp14>MUST</bcp14> be specified in a Public-Key or <t>The symmetric cipher used <bcp14>MUST</bcp14> be specified in a Pub
Symmetric-Key Encrypted Session Key packet that precedes the Symmetrically Encr lic Key or Symmetric Key Encrypted Session Key packet that precedes the Symmetri
ypted Integrity Protected Data packet. cally Encrypted and Integrity Protected Data packet. In either case, the cipher
In either case, the cipher algorithm ID is prefixed to the session key before it algorithm ID is prefixed to the session key before it is encrypted.</t>
is encrypted.</t> <t>The data is encrypted in CFB mode (see <xref target="cfb-mode"/>).
The IV is specified as all zeros. Instead of achieving randomized encryption thr
<t>The data is encrypted in CFB mode (see <xref target="cfb-mode"/>). ough an IV, OpenPGP prefixes an octet string to the data before it is encrypted
The Initial Vector (IV) is specified as all zeros. for this purpose.
Instead of achieving randomized encryption through an IV, OpenPGP prefixes an oc
tet string to the data before it is encrypted for this purpose.
The length of the octet string equals the block size of the cipher in octets, pl us two. The length of the octet string equals the block size of the cipher in octets, pl us two.
The first octets in the group, of length equal to the block size of the cipher, are random; the last two octets are each copies of their 2nd preceding octet. The first octets in the group, of length equal to the block size of the cipher, are random; the last two octets are each copies of their 2nd preceding octet.
For example, with a cipher whose block size is 128 bits or 16 octets, the prefix data will contain 16 random octets, then two more octets, which are copies of t he 15th and 16th octets, respectively. For example, with a cipher whose block size is 128 bits or 16 octets, the prefix data will contain 16 random octets, then two more octets, which are copies of t he 15th and 16th octets, respectively.
Unlike the deprecated Symmetrically Encrypted Data packet (<xref target="sed"/>) , this prefix data is encrypted in the same CFB context, and no special CFB resy nchronization is done.</t> Unlike the deprecated Symmetrically Encrypted Data packet (<xref target="sed"/>) , this prefix data is encrypted in the same CFB context, and no special CFB resy nchronization is done.</t>
<t>The repetition of 16 bits in the random data prefixed to the messag
<t>The repetition of 16 bits in the random data prefixed to the message allows t e allows the receiver to immediately check whether the session key is incorrect.
he receiver to immediately check whether the session key is incorrect.
See <xref target="quick-check-oracle"/> for hints on the proper use of this "qui ck check".</t> See <xref target="quick-check-oracle"/> for hints on the proper use of this "qui ck check".</t>
<t>Two constant octets with the values 0xD3 and 0x14 are appended to t
<t>Two constant octets with the values 0xD3 and 0x14 are appended to the plainte he plaintext. Then, the plaintext of the data to be encrypted is passed through
xt. the SHA-1 hash function. The input to the hash function is comprised of the pref
Then, the plaintext of the data to be encrypted is passed through the SHA-1 hash ix data described above and all of the plaintext, including the trailing constan
function. t octets 0xD3, 0x14.
The input to the hash function includes the prefix data described above; it incl
udes all of the plaintext, including the trailing constant octets 0xD3, 0x14.
The 20 octets of the SHA-1 hash are then appended to the plaintext (after the co nstant octets 0xD3, 0x14) and encrypted along with the plaintext using the same CFB context. The 20 octets of the SHA-1 hash are then appended to the plaintext (after the co nstant octets 0xD3, 0x14) and encrypted along with the plaintext using the same CFB context.
This trailing checksum is known as the Modification Detection Code (MDC).</t> This trailing checksum is known as the Modification Detection Code (MDC).</t>
<t>During decryption, the plaintext data should be hashed with SHA-1,
including the prefix data as well as the trailing constant octets 0xD3, 0x14, bu
t excluding the last 20 octets containing the SHA-1 hash. The computed SHA-1 has
h is then compared with the last 20 octets of plaintext.
A mismatch of the hash indicates that the message has been modified and <bcp14>M
UST</bcp14> be treated as a security problem. Any failure <bcp14>SHOULD</bcp14>
be reported to the user.</t>
<t>During decryption, the plaintext data should be hashed with SHA-1, including <t indent="3">NON-NORMATIVE EXPLANATION</t>
the prefix data as well as the trailing constant octets 0xD3, 0x14, but excludin <t indent="3">The MDC system, as the integrity
g the last 20 octets containing the SHA-1 hash. protection mechanism of the version 1 Symmetrically Encrypted
The computed SHA-1 hash is then compared with the last 20 octets of plaintext. and Integrity Protected Data packet is called, was created to
A mismatch of the hash indicates that the message has been modified and <bcp14>M
UST</bcp14> be treated as a security problem.
Any failure <bcp14>SHOULD</bcp14> be reported to the user.</t>
<ul empty="true"><li>
<t>NON-NORMATIVE EXPLANATION</t>
<t>The Modification Detection Code (MDC) system, as the integrity
protection mechanism of version 1 of the Symmetrically Encrypted
Integrity Protected Data packet is called, was created to
provide an integrity mechanism that is less strong than a provide an integrity mechanism that is less strong than a
signature, yet stronger than bare CFB encryption.</t> signature, yet stronger than bare CFB encryption.</t>
<t indent="3">CFB encryption has a limitation as damage to the cip
<t>It is a limitation of CFB encryption that damage to the ciphertext hertext
will corrupt the affected cipher blocks and the block following. will corrupt the affected cipher blocks and the block following.
Additionally, if data is removed from the end of a CFB-encrypted Additionally, if data is removed from the end of a CFB-encrypted
block, that removal is undetectable. (Note also that CBC mode has block, that removal is undetectable. (Note also that CBC mode has
a similar limitation, but data removed from the front of the block a similar limitation, but data removed from the front of the block
is undetectable.)</t> is undetectable.)</t>
<t indent="3">The obvious way to protect or authenticate an encryp
<t>The obvious way to protect or authenticate an encrypted block is ted block is
to digitally sign it. However, many people do not wish to to digitally sign it. However, many people do not wish to
habitually sign data, for a large number of reasons beyond the habitually sign data for a large number of reasons that are beyond the
scope of this document. Suffice it to say that many people scope of this document. Suffice it to say that many people
consider properties such as deniability to be as valuable as consider properties such as deniability to be as valuable as
integrity.</t> integrity.</t>
<t indent="3">OpenPGP addresses this desire to have more security
<t>OpenPGP addresses this desire to have more security than raw than raw
encryption and yet preserve deniability with the MDC system. An encryption and yet preserve deniability with the MDC system. An
MDC is intentionally not a MAC. Its name was not selected by MDC is intentionally not a Message Authentication Code (MAC). Its name was no t selected by
accident. It is analogous to a checksum.</t> accident. It is analogous to a checksum.</t>
<t indent="3">Despite the fact that it is a relatively modest syst
<t>Despite the fact that it is a relatively modest system, it has em, it has
proved itself in the real world. It is an effective defense to proved itself in the real world. It is an effective defense to
several attacks that have surfaced since it has been created. It several attacks that have surfaced since it has been created. It
has met its modest goals admirably.</t> has met its modest goals admirably.</t>
<t indent="3">Consequently, because it is a modest security system
<t>Consequently, because it is a modest security system, it has , it has
modest requirements on the hash function(s) it employs. It does modest requirements on the hash function(s) it employs. It does
not rely on a hash function being collision-free, it relies on a not rely on a hash function being collision-free; it relies on a
hash function being one-way. If a forger, Frank, wishes to send hash function being one-way. If a forger, Frank, wishes to send
Alice a (digitally) unsigned message that says, "I've always Alice a (digitally) unsigned message that says, "I've always
secretly loved you, signed Bob", it is far easier for him to secretly loved you, signed Bob", it is far easier for him to
construct a new message than it is to modify anything intercepted construct a new message than it is to modify anything intercepted
from Bob. (Note also that if Bob wishes to communicate secretly from Bob. (Note also that if Bob wishes to communicate secretly
with Alice, but without authentication or identification and with with Alice, but without authentication or identification and with
a threat model that includes forgers, he has a problem that a threat model that includes forgers, he has a problem that
transcends mere cryptography.)</t> transcends mere cryptography.)</t>
<t indent="3">Note also that unlike nearly every other OpenPGP sub
<t>Note also that unlike nearly every other OpenPGP subsystem, there system, there
are no parameters in the MDC system. It hard-defines SHA-1 as its are no parameters in the MDC system. It hard-defines SHA-1 as its
hash function. This is not an accident. It is an intentional hash function. This is not an accident. It is an intentional
choice to avoid downgrade and cross-grade attacks while making a choice to avoid downgrade and cross-grade attacks while making a
simple, fast system. (A downgrade attack would be an attack that simple, fast system. (A downgrade attack is an attack that would
replaced SHA2-256 with SHA-1, for example. A cross-grade attack replace SHA2-256 with SHA-1, for example. A cross-grade attack
would replace SHA-1 with another 160-bit hash, such as would replace SHA-1 with another 160-bit hash, such as
RIPEMD-160, for example.)</t> RIPEMD-160, for example.)</t>
<t indent="3">However, no update will be needed because the MDC ha
<t>However, no update will be needed because the MDC has been replaced s been replaced
by the AEAD encryption described in this document.</t> by the AEAD encryption described in this document.</t>
</li></ul>
</section> </section>
<section anchor="version-two-seipd"><name>Version 2 Symmetrically Encrypted Inte <section anchor="version-two-seipd">
grity Protected Data Packet Format</name> <name>Version 2 Symmetrically Encrypted and Integrity Protected Data P
acket Format</name>
<t>A version 2 Symmetrically Encrypted Integrity Protected Data packet consists <t>A version 2 Symmetrically Encrypted and Integrity Protected Data pa
of:</t> cket consists of:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>A one-octet version number with value 2.</t> <t>A 1-octet version number with value 2.</t>
<t>A one-octet cipher algorithm ID.</t> </li>
<t>A one-octet AEAD algorithm identifier.</t> <li>
<t>A one-octet chunk size.</t> <t>A 1-octet cipher algorithm ID.</t>
<t>Thirty-two octets of salt. </li>
The salt is used to derive the message key and <bcp14>MUST</bcp14> be securely g <li>
enerated (See <xref target="CSPRNG"/>).</t> <t>A 1-octet AEAD algorithm identifier.</t>
<t>Encrypted data, the output of the selected symmetric-key cipher operating i </li>
n the given AEAD mode.</t> <li>
<t>A final, summary authentication tag for the AEAD mode.</t> <t>A 1-octet chunk size.</t>
</list></t> </li>
<li>
<t>The decrypted session key and the salt are used to derive an M-bit message ke <t>32 octets of salt.
y and N-64 bits used as initialization vector, where M is the key size of the sy The salt is used to derive the message key and <bcp14>MUST</bcp14> be securely g
mmetric algorithm and N is the nonce size of the AEAD algorithm. enerated (see <xref target="CSPRNG"/>).</t>
M + N - 64 bits are derived using HKDF (see <xref target="RFC5869"/>). </li>
The left-most M bits are used as symmetric algorithm key, the remaining N - 64 b <li>
its are used as initialization vector. <t>Encrypted data; that is, the output of the selected symmetric k
HKDF is used with SHA256 (<xref target="RFC6234"/>) as hash algorithm, the sessi ey cipher operating in the given AEAD mode.</t>
on key as Initial Keying Material (IKM), the salt as salt, and the Packet Type I </li>
D in OpenPGP format encoding (bits 7 and 6 set, bits 5-0 carry the packet type I <li>
D), version number, cipher algorithm ID, AEAD algorithm ID, and chunk size octet <t>A final summary authentication tag for the AEAD mode.</t>
as info parameter.</t> </li>
</ul>
<t>The KDF mechanism provides key separation between cipher and AEAD algorithms. <t>The decrypted session key and the salt are used to derive an M-bit
Furthermore, an implementation can securely reply to a message even if a recipie message key and N-64 bits used as the IV, where M is the key size of the symmetr
nt's certificate is unknown by reusing the encrypted session key packets and rep ic algorithm and N is the nonce size of the AEAD algorithm. M + N - 64 bits are
lying with a different salt yielding a new, unique message key. derived using HKDF (see <xref target="RFC5869"/>). The leftmost M bits are used
as a symmetric algorithm key, and the remaining N - 64 bits are used as an IV. H
KDF is used with SHA256 <xref target="RFC6234"/> as hash algorithm. The session
key is used as IKM and the salt as salt. The Packet Type ID in OpenPGP format en
coding (bits 7 and 6 are set, and bits 5-0 carry the Packet Type ID), version nu
mber, cipher algorithm ID, AEAD algorithm ID, and chunk size octet are used as i
nfo parameter.</t>
<t>The KDF mechanism provides key separation between cipher and AEAD a
lgorithms.
Furthermore, an implementation can securely reply to a message even if a recipie
nt's certificate is unknown by reusing the Encrypted Session Key packets and rep
lying with a different salt that yields a new, unique message key.
See <xref target="secure-sessionkey-reuse"/> for guidance on how applications ca n securely implement this feature.</t> See <xref target="secure-sessionkey-reuse"/> for guidance on how applications ca n securely implement this feature.</t>
<t>A v2 SEIPD packet consists of one or more chunks of data. The plain
<t>A v2 SEIPD packet consists of one or more chunks of data. text of each chunk is of a size specified by the chunk size octet using the meth
The plaintext of each chunk is of a size specified using the chunk size octet us od specified below.</t>
ing the method specified below.</t> <t>The encrypted data consists of the encryption of each chunk of plai
ntext, followed immediately by the relevant authentication tag. If the last chun
<t>The encrypted data consists of the encryption of each chunk of plaintext, fol k of plaintext is smaller than the chunk size, the ciphertext for that data may
lowed immediately by the relevant authentication tag. be shorter; nevertheless, it is followed by a full authentication tag.</t>
If the last chunk of plaintext is smaller than the chunk size, the ciphertext fo <t>For each chunk, the AEAD construction is given the Packet Type ID e
r that data may be shorter; it is nevertheless followed by a full authentication ncoded in OpenPGP format (bits 7 and 6 are set, and bits 5-0 carry the Packet Ty
tag.</t> pe ID), version number, cipher algorithm ID, AEAD algorithm ID, and chunk size o
ctet as additional data.
<t>For each chunk, the AEAD construction is given the Packet Type ID encoded in For example, the additional data of the first chunk using EAX and AES-128 with a
OpenPGP format (bits 7 and 6 set, bits 5-0 carry the packet type ID), version nu chunk size of 2<sup>22</sup> octets consists of the octets 0xD2, 0x02, 0x07, 0x
mber, cipher algorithm ID, AEAD algorithm ID, and chunk size octet as additional 01, and 0x10.</t>
data. <t>After the final chunk, the AEAD algorithm is used to produce a fina
For example, the additional data of the first chunk using EAX and AES-128 with a l authentication tag encrypting the empty string.
chunk size of 2**22 octets consists of the octets 0xD2, 0x02, 0x07, 0x01, and 0 This AEAD instance is given the additional data specified above, plus an 8-octet
x10.</t> , big-endian value specifying the total number of plaintext octets encrypted. Th
is allows detection of a truncated ciphertext.</t>
<t>After the final chunk, the AEAD algorithm is used to produce a final authenti <t>The chunk size octet specifies the size of chunks using the followi
cation tag encrypting the empty string. ng formula (in C <xref target="C99"/>), where c is the chunk size octet:</t>
This AEAD instance is given the additional data specified above, plus an eight-o <artwork><![CDATA[
ctet, big-endian value specifying the total number of plaintext octets encrypted
.
This allows detection of a truncated ciphertext.</t>
<t>The chunk size octet specifies the size of chunks using the following formula
(in <xref target="C99"/>), where c is the chunk size octet:</t>
<figure><artwork><![CDATA[
chunk_size = (uint32_t) 1 << (c + 6) chunk_size = (uint32_t) 1 << (c + 6)
]]></artwork></figure> ]]></artwork>
<t>An implementation <bcp14>MUST</bcp14> accept chunk size octets with
<t>An implementation <bcp14>MUST</bcp14> accept chunk size octets with values fr values from 0 to 16.
om 0 to 16.
An implementation <bcp14>MUST NOT</bcp14> create data with a chunk size octet va lue larger than 16 (4 MiB chunks).</t> An implementation <bcp14>MUST NOT</bcp14> create data with a chunk size octet va lue larger than 16 (4 MiB chunks).</t>
<t>The nonce for AEAD mode consists of two parts.
<t>The nonce for AEAD mode consists of two parts. Let N be the size of the nonce. The leftmost N - 64 bits are the IV derived usin
Let N be the size of the nonce. g HKDF.
The left-most N - 64 bits are the initialization vector derived using HKDF. The rightmost 64 bits are the chunk index as a big-endian value.
The right-most 64 bits are the chunk index as big-endian value.
The index of the first chunk is zero.</t> The index of the first chunk is zero.</t>
</section>
</section> <section anchor="aead-mode-eax">
<section anchor="aead-mode-eax"><name>EAX Mode</name> <name>EAX Mode</name>
<t>The EAX AEAD algorithm used in this document is defined in <xref ta
<t>The EAX AEAD Algorithm used in this document is defined in <xref target="EAX" rget="EAX"/>.</t>
/>.</t> <t>The EAX algorithm can only use block ciphers with 16-octet blocks.
<t>The EAX algorithm can only use block ciphers with 16-octet blocks.
The nonce is 16 octets long. The nonce is 16 octets long.
EAX authentication tags are 16 octets long.</t> EAX authentication tags are 16 octets long.</t>
</section>
</section> <section anchor="aead-mode-ocb">
<section anchor="aead-mode-ocb"><name>OCB Mode</name> <name>OCB Mode</name>
<t>The OCB AEAD algorithm used in this document is defined in <xref ta
<t>The OCB AEAD Algorithm used in this document is defined in <xref target="RFC7 rget="RFC7253"/>.</t>
253"/>.</t> <t>The OCB algorithm can only use block ciphers with 16-octet blocks.
<t>The OCB algorithm can only use block ciphers with 16-octet blocks.
The nonce is 15 octets long. The nonce is 15 octets long.
OCB authentication tags are 16 octets long.</t> OCB authentication tags are 16 octets long.</t>
</section>
</section> <section anchor="aead-mode-gcm">
<section anchor="aead-mode-gcm"><name>GCM Mode</name> <name>GCM Mode</name>
<t>The GCM AEAD algorithm used in this document is defined in <xref ta
<t>The GCM AEAD Algorithm used in this document is defined in <xref target="SP80 rget="SP800-38D"/>.</t>
0-38D"/>.</t> <t>The GCM algorithm can only use block ciphers with 16-octet blocks.
<t>The GCM algorithm can only use block ciphers with 16-octet blocks.
The nonce is 12 octets long. The nonce is 12 octets long.
GCM authentication tags are 16 octets long.</t> GCM authentication tags are 16 octets long.</t>
</section>
</section> </section>
</section> <section anchor="padding-packet">
<section anchor="padding-packet"><name>Padding Packet (Type ID 21)</name> <name>Padding Packet (Type ID 21)</name>
<t>The Padding packet contains random data and can be used to defend aga
<t>The Padding packet contains random data, and can be used to defend against tr inst traffic analysis (see <xref target="traffic-analysis"/>) on v2 SEIPD messag
affic analysis (see <xref target="traffic-analysis"/>) on version 2 SEIPD messag es (see <xref target="version-two-seipd"/>) and Transferable Public Keys (see <x
es (see <xref target="version-two-seipd"/>) and Transferable Public Keys (see <x ref target="transferable-public-keys"/>).</t>
ref target="transferable-public-keys"/>).</t> <t>Such a packet <bcp14>MUST</bcp14> be ignored when received.</t>
<t>Its contents <bcp14>SHOULD</bcp14> be random octets to make the lengt
<t>Such a packet <bcp14>MUST</bcp14> be ignored when received.</t> h obfuscation it provides more robust even when compressed.</t>
<t>An implementation adding padding to an OpenPGP stream <bcp14>SHOULD</
<t>Its contents <bcp14>SHOULD</bcp14> be random octets to make the length obfusc bcp14> place such a packet:</t>
ation it provides more robust even when compressed.</t> <ul spacing="normal">
<li>
<t>An implementation adding padding to an OpenPGP stream <bcp14>SHOULD</bcp14> p <t>At the end of a version 6 Transferable Public Key that is transfe
lace such a packet:</t> rred over an encrypted channel (see <xref target="transferable-public-keys"/>).<
/t>
<t><list style="symbols"> </li>
<t>At the end of a v6 Transferable Public Key that is transferred over an encr <li>
ypted channel (see <xref target="transferable-public-keys"/>).</t> <t>As the last packet of an Optionally Padded Message within a versi
<t>As the last packet of an Optionally Padded Message within a version 2 Symme on 2 Symmetrically Encrypted and Integrity Protected Data packet (see <xref targ
trically Encrypted Integrity Protected Data packet (see <xref target="unwrapping et="unwrapping"/>).</t>
"/>).</t> </li>
</list></t> </ul>
<t>An implementation <bcp14>MUST</bcp14> be able to process Padding pack
<t>An implementation <bcp14>MUST</bcp14> be able to process padding packets anyw ets anywhere else in an OpenPGP stream so that future revisions of this document
here else in an OpenPGP stream, so that future revisions of this document may sp may specify further locations for padding.</t>
ecify further locations for padding.</t> <t>Policy about how large to make such a packet to defend against traffi
c analysis is beyond the scope of this document.</t>
<t>Policy about how large to make such a packet to defend against traffic analys </section>
is is beyond the scope of this document.</t> </section>
<section anchor="base64">
</section> <name>Base64 Conversions</name>
</section> <t>As stated in the introduction, OpenPGP's underlying representation for
<section anchor="base64"><name>Base64 Conversions</name> objects is a stream of arbitrary octets, and some systems desire these objects t
o be immune to damage caused by character set translation, data conversions, etc
<t>As stated in the introduction, OpenPGP's underlying native representation for .</t>
objects is a stream of arbitrary octets, and some systems desire these objects <t>In principle, any printable encoding scheme that met the requirements o
to be immune to damage caused by character set translation, data conversions, et f the unsafe channel would suffice, since it would not change the underlying bin
c.</t> ary bit streams of the OpenPGP data structures.
The OpenPGP specification specifies one such printable encoding scheme to ensure
<t>In principle, any printable encoding scheme that met the requirements of the interoperability; see <xref target="forming-ascii-armor"/>.</t>
unsafe channel would suffice, since it would not change the underlying binary bi <t>The encoding is composed of two parts: a base64 encoding of the binary
t streams of the native OpenPGP data structures. data and an optional checksum.
The OpenPGP standard specifies one such printable encoding scheme to ensure inte
roperability, <xref target="forming-ascii-armor"/>.</t>
<t>The encoding is composed of two parts: a base64 encoding of the binary data a
nd an optional checksum.
The base64 encoding used is described in <xref section="4" sectionFormat="of" ta rget="RFC4648"/>, and it is wrapped into lines of no more than 76 characters eac h.</t> The base64 encoding used is described in <xref section="4" sectionFormat="of" ta rget="RFC4648"/>, and it is wrapped into lines of no more than 76 characters eac h.</t>
<t>When decoding base64, an OpenPGP implementation <bcp14>MUST</bcp14> ign
<t>When decoding base64, an OpenPGP implementation <bcp14>MUST</bcp14> ignore al ore all whitespace.</t>
l white space.</t> <section anchor="optional-crc24">
<name>Optional Checksum</name>
<section anchor="optional-crc24"><name>Optional checksum</name> <t>The optional checksum is a 24-bit Cyclic Redundancy Check (CRC) conve
rted to four characters of base64 encoding by the same MIME base64 transformatio
<t>The optional checksum is a 24-bit Cyclic Redundancy Check (CRC) converted to n, preceded by an equal sign (=). The CRC is computed by using the generator 0x8
four characters of base64 encoding by the same MIME base64 transformation, prece 64CFB and an initialization of 0xB704CE. The accumulation is done on the data be
ded by an equal sign (=). fore it is converted to base64 rather than on the converted data. A sample imple
The CRC is computed by using the generator 0x864CFB and an initialization of 0xB mentation of this algorithm is in <xref target="sample-crc24"/>.</t>
704CE. <t>If present, the checksum with its leading equal sign <bcp14>MUST</bcp14> appe
The accumulation is done on the data before it is converted to base64, rather th ar on the next line after the base64-encoded data.</t>
an on the converted data. <t>An implementation <bcp14>MUST NOT</bcp14> reject an OpenPGP object when the C
A sample implementation of this algorithm is in <xref target="sample-crc24"/>.</ RC24 footer is present, missing, malformed, or disagrees with the computed CRC24
t> sum. When forming ASCII Armor, the CRC24 footer <bcp14>SHOULD NOT</bcp14> be ge
nerated, unless interoperability with implementations that require the CRC24 foo
<t>If present, the checksum with its leading equal sign <bcp14>MUST</bcp14> appe ter to be present is a concern.</t>
ar on the next line after the base64 encoded data.</t> <t>The CRC24 footer <bcp14>MUST NOT</bcp14> be generated if it can be de
termined by the context or by the OpenPGP object being encoded that the consumin
<t>An implementation <bcp14>MUST NOT</bcp14> reject an OpenPGP object when the C g implementation accepts base64-encoded blocks without a CRC24 footer. Notably:<
RC24 footer is present, missing, malformed, or disagrees with the computed CRC24 /t>
sum. <ul spacing="normal">
When forming ASCII Armor, the CRC24 footer <bcp14>SHOULD NOT</bcp14> be generate <li>
d, unless interoperability with implementations that require the CRC24 footer to <t>An ASCII-armored Encrypted Message packet sequence that ends in a
be present is a concern.</t> v2 SEIPD packet <bcp14>MUST NOT</bcp14> contain a CRC24 footer.</t>
</li>
<t>The CRC24 footer <bcp14>MUST NOT</bcp14> be generated if it can be determined <li>
by context or by the OpenPGP object being encoded that the consuming implementa <t>An ASCII-armored sequence of Signature packets that only includes
tion accepts base64 encoded blocks without CRC24 footer. version 6 Signature packets <bcp14>MUST NOT</bcp14> contain a CRC24 footer.</t>
Notably:</t> </li>
<li>
<t><list style="symbols"> <t>An ASCII-armored Transferable Public Key packet sequence of a ver
<t>An ASCII-armored Encrypted Message packet sequence that ends in an v2 SEIPD sion 6 key <bcp14>MUST NOT</bcp14> contain a CRC24 footer.</t>
packet <bcp14>MUST NOT</bcp14> contain a CRC24 footer.</t> </li>
<t>An ASCII-armored sequence of Signature packets that only includes v6 Signat <li>
ure packets <bcp14>MUST NOT</bcp14> contain a CRC24 footer.</t> <t>An ASCII-armored keyring consisting of only version 6 keys <bcp14
<t>An ASCII-armored Transferable Public Key packet sequence of a v6 key <bcp14 >MUST NOT</bcp14> contain a CRC24 footer.</t>
>MUST NOT</bcp14> contain a CRC24 footer.</t> </li>
<t>An ASCII-armored keyring consisting of only v6 keys <bcp14>MUST NOT</bcp14> </ul>
contain a CRC24 footer.</t> <t>Rationale:
</list></t> Previous draft versions of this document stated that the CRC24 footer is optiona
l, but the text was ambiguous. In practice, very few implementations require the
<t>Rationale: CRC24 footer to be present. Computing the CRC24 incurs a significant cost, whil
Previous versions of this document state that the CRC24 footer is optional, but e providing no meaningful integrity protection.
the text was ambiguous.
In practice, very few implementations require the CRC24 footer to be present.
Computing the CRC24 incurs a significant cost, while providing no meaningful int
egrity protection.
Therefore, generating it is now discouraged.</t> Therefore, generating it is now discouraged.</t>
<section anchor="sample-crc24">
<section anchor="sample-crc24"><name>An Implementation of the CRC-24 in "C"</nam <name>An Implementation of the CRC24 in "C"</name>
e> <t>The following code is written in <xref target="C99"/>.</t>
<sourcecode type="text/c" name="sample-crc24.c"><![CDATA[
<t>The following code is written in <xref target="C99"/>.</t>
<figure><sourcecode type="text/x-csrc" name="sample-crc24.c"><![CDATA[
#define CRC24_INIT 0xB704CEL #define CRC24_INIT 0xB704CEL
#define CRC24_GENERATOR 0x864CFBL #define CRC24_GENERATOR 0x864CFBL
typedef unsigned long crc24; typedef unsigned long crc24;
crc24 crc_octets(unsigned char *octets, size_t len) crc24 crc_octets(unsigned char *octets, size_t len)
{ {
crc24 crc = CRC24_INIT; crc24 crc = CRC24_INIT;
int i; int i;
while (len--) { while (len--) {
crc ^= (*octets++) << 16; crc ^= (*octets++) << 16;
for (i = 0; i < 8; i++) { for (i = 0; i < 8; i++) {
crc <<= 1; crc <<= 1;
if (crc & 0x1000000) { if (crc & 0x1000000) {
crc &= 0XFFFFFF; /* Clear bit 25 to avoid overflow */ crc &= 0XFFFFFF; /* Clear bit 25 to avoid overflow */
crc ^= CRC24_GENERATOR; crc ^= CRC24_GENERATOR;
} }
} }
} }
return crc & 0xFFFFFFL; return crc & 0xFFFFFFL;
} }
]]></sourcecode></figure> ]]></sourcecode>
</section>
</section> </section>
</section> <section anchor="forming-ascii-armor">
<section anchor="forming-ascii-armor"><name>Forming ASCII Armor</name> <name>Forming ASCII Armor</name>
<t>When OpenPGP encodes data into ASCII Armor, it puts specific headers
<t>When OpenPGP encodes data into ASCII Armor, it puts specific headers around t around the base64-encoded data, so OpenPGP can reconstruct the data later.
he base64 encoded data, so OpenPGP can reconstruct the data later. An OpenPGP implementation <bcp14>MAY</bcp14> use ASCII Armor to protect raw bina
An OpenPGP implementation <bcp14>MAY</bcp14> use ASCII armor to protect raw bina ry data.
ry data. OpenPGP informs the user what kind of data is encoded in the ASCII Armor through
OpenPGP informs the user what kind of data is encoded in the ASCII armor through the use of the headers.</t>
the use of the headers.</t> <t>Concatenating the following data creates ASCII Armor:</t>
<ul spacing="normal">
<t>Concatenating the following data creates ASCII Armor:</t> <li>
<t>An Armor Header Line, appropriate for the type of data</t>
<t><list style="symbols"> </li>
<t>An Armor Header Line, appropriate for the type of data</t> <li>
<t>Armor Headers</t> <t>Armor Headers</t>
<t>A blank (zero-length, or containing only whitespace) line</t> </li>
<t>The ASCII-Armored data</t> <li>
<t>An optional Armor Checksum (discouraged, see <xref target="optional-crc24"/ <t>A blank (zero length or containing only whitespace) line</t>
>)</t> </li>
<t>The Armor Tail, which depends on the Armor Header Line</t> <li>
</list></t> <t>The ASCII-Armored data</t>
</li>
<section anchor="armor-header-line"><name>Armor Header Line</name> <li>
<t>An optional Armor Checksum (discouraged; see <xref target="option
<t>An Armor Header Line consists of the appropriate header line text surrounded al-crc24"/>)</t>
by five (5) dashes (<spanx style="verb">-</spanx>, 0x2D) on either side of the h </li>
eader line text. <li>
The header line text is chosen based upon the type of data that is being encoded <t>The Armor Tail, which depends on the Armor Header Line</t>
in Armor, and how it is being encoded. </li>
</ul>
<section anchor="armor-header-line">
<name>Armor Header Line</name>
<t>An Armor Header Line consists of the appropriate header line text s
urrounded by five (5) dashes (<tt>-</tt>, 0x2D) on either side of the header lin
e text. The header line text is chosen based on the type of data being encoded i
n Armor and how it is being encoded.
Header line texts include the following strings:</t> Header line texts include the following strings:</t>
<texttable title="OpenPGP Armor Header Line registry" anchor="armor-header-line- <table anchor="armor-header-line-registry">
registry"> <name>OpenPGP Armor Header Lines Registry</name>
<ttcol align='left'>Armor Header</ttcol> <thead>
<ttcol align='left'>Use</ttcol> <tr>
<c><spanx style="verb">BEGIN PGP MESSAGE</spanx></c> <th align="left">Armor Header</th>
<c>Used for signed, encrypted, or compressed files.</c> <th align="left">Use</th>
<c><spanx style="verb">BEGIN PGP PUBLIC KEY BLOCK</spanx></c> </tr>
<c>Used for armoring public keys.</c> </thead>
<c><spanx style="verb">BEGIN PGP PRIVATE KEY BLOCK</spanx></c> <tbody>
<c>Used for armoring private keys.</c> <tr>
<c><spanx style="verb">BEGIN PGP SIGNATURE</spanx></c> <td align="left">
<c>Used for detached signatures, OpenPGP/MIME signatures, and cleartext si <tt>BEGIN PGP MESSAGE</tt></td>
gnatures.</c> <td align="left">Used for signed, encrypted, or compressed files
</texttable> .</td>
</tr>
<t>Note that all these Armor Header Lines are to consist of a complete line. <tr>
The header lines, therefore, <bcp14>MUST</bcp14> start at the beginning of a lin <td align="left">
e, and <bcp14>MUST NOT</bcp14> have text other than whitespace following them on <tt>BEGIN PGP PUBLIC KEY BLOCK</tt></td>
the same line.</t> <td align="left">Used for armoring public keys.</td>
</tr>
</section> <tr>
<section anchor="armor-headers"><name>Armor Headers</name> <td align="left">
<tt>BEGIN PGP PRIVATE KEY BLOCK</tt></td>
<t>The Armor Headers are pairs of strings that can give the user or the receivin <td align="left">Used for armoring private keys.</td>
g OpenPGP implementation some information about how to decode or use the message </tr>
. <tr>
The Armor Headers are a part of the armor, not a part of the message, and hence <td align="left">
are not protected by any signatures applied to the message.</t> <tt>BEGIN PGP SIGNATURE</tt></td>
<td align="left">Used for detached signatures, OpenPGP/MIME sign
<t>The format of an Armor Header is that of a key-value pair. atures, and cleartext signatures.</td>
A colon (<spanx style="verb">:</spanx> 0x3A) and a single space (0x20) separate </tr>
the key and value. </tbody>
An OpenPGP implementation may consider improperly formatted Armor Headers to be </table>
corruption of the ASCII Armor, but <bcp14>SHOULD</bcp14> make an effort to recov <t>Note that all of these Armor Header Lines are to consist of a compl
er. ete line.
Unknown keys should be silently ignored, and an OpenPGP implementation <bcp14>SH Therefore, the header lines <bcp14>MUST</bcp14> start at the beginning of a line
OULD</bcp14> continue to process the message.</t> and <bcp14>MUST NOT</bcp14> have text other than whitespace following them on t
he same line.</t>
<t>Note that some transport methods are sensitive to line length. </section>
<section anchor="armor-headers">
<name>Armor Headers</name>
<t>The Armor Headers are pairs of strings that can give the user or th
e receiving OpenPGP implementation some information about how to decode or use t
he message. The Armor Headers are a part of the armor, not the message, and henc
e are not protected by any signatures applied to the message.</t>
<t>The format of an Armor Header is that of a key-value pair. A colon
(<tt>:</tt> 0x3A) and a single space (0x20) separate the key and value.
An OpenPGP implementation may consider improperly formatted Armor Headers to be
a corruption of the ASCII Armor, but it <bcp14>SHOULD</bcp14> make an effort to
recover. Unknown keys should be silently ignored, and an OpenPGP implementation
<bcp14>SHOULD</bcp14> continue to process the message.</t>
<t>Note that some transport methods are sensitive to line length.
For example, the SMTP protocol that transports email messages has a line length limit of 998 characters (see <xref section="2.1.1" sectionFormat="of" target="RF C5322"/>).</t> For example, the SMTP protocol that transports email messages has a line length limit of 998 characters (see <xref section="2.1.1" sectionFormat="of" target="RF C5322"/>).</t>
<t>While there is a limit of 76 characters for the base64 data (<xref
<t>While there is a limit of 76 characters for the base64 data (<xref target="ba target="base64"/>), there is no limit for the length of Armor Headers.
se64"/>), there is no limit to the length of Armor Headers. Care should be taken to ensure that the Armor Headers are short enough to surviv
Care should be taken that the Armor Headers are short enough to survive transpor e transport.
t.
One way to do this is to repeat an Armor Header Key multiple times with differen t values for each so that no one line is overly long.</t> One way to do this is to repeat an Armor Header Key multiple times with differen t values for each so that no one line is overly long.</t>
<t>Currently defined Armor Header Keys are as follows:</t>
<t>Currently defined Armor Header Keys are as follows:</t> <table anchor="armor-header-key-registry">
<name>OpenPGP Armor Header Keys Registry</name>
<texttable title="OpenPGP Armor Header Key registry" anchor="armor-header-key-re <thead>
gistry"> <tr>
<ttcol align='left'>Key</ttcol> <th align="left">Key</th>
<ttcol align='left'>Summary</ttcol> <th align="left">Summary</th>
<ttcol align='left'>Reference</ttcol> <th align="left">Reference</th>
<c><spanx style="verb">Version</spanx></c> </tr>
<c>Implementation information</c> </thead>
<c><xref target="armor-header-key-version"/></c> <tbody>
<c><spanx style="verb">Comment</spanx></c> <tr>
<c>Arbitrary text</c> <td align="left">
<c><xref target="armor-header-key-comment"/></c> <tt>Version</tt></td>
<c><spanx style="verb">Hash</spanx></c> <td align="left">Implementation information</td>
<c>Hash algorithms used in some v4 cleartext signed messages</c> <td align="left">
<c><xref target="armor-header-key-hash"/></c> <xref target="armor-header-key-version"/></td>
<c><spanx style="verb">Charset</spanx></c> </tr>
<c>Character set</c> <tr>
<c><xref target="armor-header-key-charset"/></c> <td align="left">
</texttable> <tt>Comment</tt></td>
<td align="left">Arbitrary text</td>
<section anchor="armor-header-key-version"><name>"Version" Armor Header</name> <td align="left">
<xref target="armor-header-key-comment"/></td>
<t>The armor header key <spanx style="verb">Version</spanx> describes the OpenPG </tr>
P implementation and version used to encode the message. <tr>
<td align="left">
<tt>Hash</tt></td>
<td align="left">Hash algorithms used in some v4 cleartext signe
d messages</td>
<td align="left">
<xref target="armor-header-key-hash"/></td>
</tr>
<tr>
<td align="left">
<tt>Charset</tt></td>
<td align="left">Character set</td>
<td align="left">
<xref target="armor-header-key-charset"/></td>
</tr>
</tbody>
</table>
<section anchor="armor-header-key-version">
<name>"Version" Armor Header</name>
<t>The Armor Header Key <tt>Version</tt> describes the OpenPGP imple
mentation and version used to encode the message.
To minimize metadata, implementations <bcp14>SHOULD NOT</bcp14> emit this key an d its corresponding value except for debugging purposes with explicit user conse nt.</t> To minimize metadata, implementations <bcp14>SHOULD NOT</bcp14> emit this key an d its corresponding value except for debugging purposes with explicit user conse nt.</t>
</section>
</section> <section anchor="armor-header-key-comment">
<section anchor="armor-header-key-comment"><name>"Comment" Armor Header</name> <name>"Comment" Armor Header</name>
<t>The Armor Header Key <tt>Comment</tt> supplies a user-defined com
<t>The armor header key <spanx style="verb">Comment</spanx> supplies a user-defi ment.
ned comment. OpenPGP defines all text to be in UTF-8. A comment may be any UTF-8 s
OpenPGP defines all text to be in UTF-8. tring. However, the whole point of armoring is to provide 7-bit clean data. Cons
A comment may be any UTF-8 string. equently, if a comment has characters that are outside the ASCII range of UTF-8,
However, the whole point of armoring is to provide seven-bit-clean data. they may very well not survive transport.</t>
Consequently, if a comment has characters that are outside the US-ASCII range of </section>
UTF, they may very well not survive transport.</t> <section anchor="armor-header-key-hash">
<name>"Hash" Armor Header</name>
</section> <t>The Armor Header Key <tt>Hash</tt> is deprecated, but some older
<section anchor="armor-header-key-hash"><name>"Hash" Armor Header</name> implementations expect it in messages using the Cleartext Signature Framework (<
xref target="cleartext-signature"/>). When present, this Armor Header Key contai
<t>This header is deprecated, but some older implementations expect it in messag ns a comma-separated list of hash algorithms used in the signatures on message,
es using the Cleartext Signature Framework (<xref target="cleartext-signature"/> with digest names as specified in the "Text Name" column in <xref target="hash-a
). lgorithms-registry"/>.
When present, The armor header key <spanx style="verb">Hash</spanx> contains a c
omma-separated list of hash algorithms used in the signatures on message, with d
igest names as specified in "Text Name" column in <xref target="hash-algorithms-
registry"/>.
These headers <bcp14>SHOULD NOT</bcp14> be emitted unless:</t> These headers <bcp14>SHOULD NOT</bcp14> be emitted unless:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>The cleartext signed message contains a v4 signature made using a SHA2-base <t>the cleartext signed message contains a version 4 signature m
d digest (<spanx style="verb">SHA224</spanx>, <spanx style="verb">SHA256</spanx> ade using a SHA2-based digest (SHA224, SHA256, SHA384, or SHA512), and</t>
, <spanx style="verb">SHA384</spanx>, or <spanx style="verb">SHA512</spanx>), an </li>
d</t> <li>
<t>The cleartext signed message might be verified by a legacy OpenPGP implemen <t>the cleartext signed message might be verified by a legacy Op
tation that requires this header.</t> enPGP implementation that requires this header.</t>
</list></t> </li>
</ul>
<t>A verifying application <bcp14>MUST</bcp14> decline to validate any signature <t>A verifying application <bcp14>MUST</bcp14> decline to validate a
in a message with a non-conformant <spanx style="verb">Hash</spanx> header (tha ny signature in a message with a non-conformant <tt>Hash</tt> header (that is, a
t is, a <spanx style="verb">Hash</spanx> header that contains anything other tha <tt>Hash</tt> header that contains anything other than a comma-separated list o
n a comma-separated list of hash algorithms). f hash algorithms).
When a conformant <spanx style="verb">Hash</spanx> header is present, a verifyin When a conformant <tt>Hash</tt> header is present, a verifying application <bcp1
g application <bcp14>MUST</bcp14> ignore its contents, deferring to the hash alg 4>MUST</bcp14> ignore its contents, deferring to the hash algorithm indicated in
orithm indicated in the embedded signature.</t> the Embedded Signature.</t>
</section>
</section> <section anchor="armor-header-key-charset">
<section anchor="armor-header-key-charset"><name>"Charset" Armor Header</name> <name>"Charset" Armor Header</name>
<t>The Armor Header Key <tt>Charset</tt> contains a description of t
<t>The armor header key <spanx style="verb">Charset</spanx> contains a descripti he character set that the plaintext is in (see <xref target="RFC2978"/>).
on of the character set that the plaintext is in (see <xref target="RFC2978"/>).
Please note that OpenPGP defines text to be in UTF-8. Please note that OpenPGP defines text to be in UTF-8.
An implementation will get best results by translating into and out of UTF-8. An implementation will get the best results by translating into and out of UTF-8 .
However, there are many instances where this is easier said than done. However, there are many instances where this is easier said than done.
Also, there are communities of users who have no need for UTF-8 because they are all happy with a character set like ISO Latin-5 or a Japanese character set. Also, there are communities of users who have no need for UTF-8 because they are all happy with a character set like ISO Latin-5 or a Japanese character set.
In such instances, an implementation <bcp14>MAY</bcp14> override the UTF-8 defau lt by using this header key. In such instances, an implementation <bcp14>MAY</bcp14> override the UTF-8 defau lt by using this header key.
An implementation <bcp14>MAY</bcp14> implement this key and any translations it cares to; an implementation <bcp14>MAY</bcp14> ignore it and assume all text is UTF-8.</t> An implementation <bcp14>MAY</bcp14> implement this key and any translations it cares to; an implementation <bcp14>MAY</bcp14> ignore it and assume all text is UTF-8.</t>
</section>
</section> </section>
</section> <section anchor="armor-tail-line">
<section anchor="armor-tail-line"><name>Armor Tail Line</name> <name>Armor Tail Line</name>
<t>The Armor Tail Line is composed in the same manner as the Armor Hea
<t>The Armor Tail Line is composed in the same manner as the Armor Header Line, der Line, except the string "BEGIN" is replaced by the string "END".</t>
except the string "BEGIN" is replaced by the string "END".</t> </section>
</section>
</section> </section>
</section> <section anchor="cleartext-signature">
</section> <name>Cleartext Signature Framework</name>
<section anchor="cleartext-signature"><name>Cleartext Signature Framework</name> <t>It is desirable to be able to sign a textual octet stream without ASCII
armoring the stream itself, so the signed text is still readable with any tool
<t>It is desirable to be able to sign a textual octet stream without ASCII armor capable of rendering text.
ing the stream itself, so the signed text is still readable with any tool capabl In order to bind a signature to such a cleartext, the Cleartext Signature Framew
e of rendering text. ork is used, which follows the same basic format and restrictions as the ASCII a
In order to bind a signature to such a cleartext, this framework is used, which rmoring described in <xref target="forming-ascii-armor"/>.
follows the same basic format and restrictions as the ASCII armoring described i
n <xref target="forming-ascii-armor"/>.
(Note that this framework is not intended to be reversible. (Note that this framework is not intended to be reversible.
<xref target="RFC3156"/> defines another way to sign cleartext messages for envi ronments that support MIME.)</t> <xref target="RFC3156"/> defines another way to sign cleartext messages for envi ronments that support MIME.)</t>
<section anchor="cleartext-structure">
<section anchor="cleartext-structure"><name>Cleartext Signed Message Structure</ <name>Cleartext Signed Message Structure</name>
name> <t>An OpenPGP cleartext signed message consists of:</t>
<ul spacing="normal">
<t>An OpenPGP cleartext signed message consists of:</t> <li>
<t>The cleartext header <tt>-----BEGIN PGP SIGNED MESSAGE-----</tt>
<t><list style="symbols"> on a single line.</t>
<t>The cleartext header <spanx style="verb">-----BEGIN PGP SIGNED MESSAGE----- </li>
</spanx> on a single line,</t> <li>
<t>Some implementations <bcp14>MAY</bcp14> include one or more legacy <spanx s <t>One or more legacy <tt>Hash</tt> Armor Headers that <bcp14>MAY</b
tyle="verb">Hash</spanx> Armor Headers, which <bcp14>MUST</bcp14> be ignored whe cp14> be included by some implementations and <bcp14>MUST</bcp14> be ignored whe
n well-formed (see <xref target="armor-header-key-hash"/>),</t> n well formed (see <xref target="armor-header-key-hash"/>).</t>
<t>An empty line (not included into the message digest),</t> </li>
<t>The dash-escaped cleartext,</t> <li>
<t>A line ending separating the cleartext and following armored signature (not <t>An empty line (not included in the message digest).</t>
included into the message digest),</t> </li>
<t>The ASCII armored signature(s) including the <spanx style="verb">-----BEGIN <li>
PGP SIGNATURE-----</spanx> Armor Header and Armor Tail Lines.</t> <t>The dash-escaped cleartext.</t>
</list></t> </li>
<li>
<t>As with any other text signature (<xref target="sigtype-text"/>), a cleartext <t>A line ending separating the cleartext and following armored sign
signature is calculated on the text using canonical &lt;CR&gt;&lt;LF&gt; line e ature (not included in the message digest).</t>
ndings. </li>
As described above, the line ending before the <spanx style="verb">-----BEGIN PG <li>
P SIGNATURE-----</spanx> Armor Header Line of the armored signature is not consi <t>The ASCII-armored signature(s), including the <tt>-----BEGIN PGP
dered part of the signed text.</t> SIGNATURE-----</tt> Armor Header and Armor Tail Lines.</t>
</li>
<t>Also, any trailing whitespace --- spaces (0x20) and tabs (0x09) --- at the en </ul>
d of any line is removed before signing or verifying a cleartext signed message. <t>As with any other Text signature (<xref target="sigtype-text"/>), a c
</t> leartext signature is calculated on the text using canonical &lt;CR&gt;&lt;LF&gt
; line endings.
<t>Between the <spanx style="verb">-----BEGIN PGP SIGNED MESSAGE-----</spanx> li As described above, the line ending before the <tt>-----BEGIN PGP SIGNATURE-----
ne and the first empty line, the only Armor Header permitted is a well-formed <s </tt> Armor Header Line of the armored signature is not considered part of the s
panx style="verb">Hash</spanx> Armor Header (see <xref target="armor-header-key- igned text.</t>
hash"/>). <t>Also, any trailing whitespace -- spaces (0x20) and tabs (0x09) -- at
the end of any line is removed before signing or verifying a cleartext signed me
ssage.</t>
<t>Between the <tt>-----BEGIN PGP SIGNED MESSAGE-----</tt> line and the
first empty line, the only Armor Header permitted is a well-formed <tt>Hash</tt>
Armor Header (see <xref target="armor-header-key-hash"/>).
To reduce the risk of confusion about what has been signed, a verifying implemen tation <bcp14>MUST</bcp14> decline to validate any signature in a cleartext mess age if that message has any other Armor Header present in this location.</t> To reduce the risk of confusion about what has been signed, a verifying implemen tation <bcp14>MUST</bcp14> decline to validate any signature in a cleartext mess age if that message has any other Armor Header present in this location.</t>
</section>
<section anchor="dash-escaping">
<name>Dash-Escaped Text</name>
<t>The cleartext content of the message must also be dash-escaped.</t>
<t>Dash-escaped cleartext is the ordinary cleartext where every line sta
rting with a <u>-</u> is prefixed by the sequence <u>-</u> and <u> </u>.
This prevents the parser from recognizing Armor Headers of the cleartext itself.
An implementation <bcp14>MAY</bcp14> dash-escape any line, <bcp14>SHOULD</bcp14>
dash-escape lines commencing in "From" followed by a space, and <bcp14>MUST</bc
p14> dash-escape any line commencing in a dash. The message digest is computed u
sing the cleartext itself, not the dash-escaped form.</t>
<t>When reversing dash-escaping, an implementation <bcp14>MUST</bcp14> s
trip the string <tt>-</tt> if it occurs at the beginning of a line, and it <bcp1
4>SHOULD</bcp14> provide a warning for <tt>-</tt> and any character other than a
space at the beginning of a line.</t>
</section>
<section anchor="csf-issues">
<name>Issues with the Cleartext Signature Framework</name>
<t>Since creating a cleartext signed message involves trimming trailing
whitespace on every line, the Cleartext Signature Framework will fail to safely
round-trip any textual stream that may include semantically meaningful whitespac
e.</t>
<t>For example, the Unified Diff format <xref target="UNIFIED-DIFF"/> co
ntains semantically meaningful whitespace: an empty line of context will consist
of a line with a single <u> </u> character, and any line that has trailing whit
espace added or removed will represent such a change with semantically meaningfu
l whitespace.</t>
<t>Furthermore, a Cleartext Signature Framework message that is very lar
ge is unlikely to work well.
In particular, it will be difficult for any human reading the message to know wh
ich part is covered by the signature because they can't understand the whole mes
sage at once, especially in the case where an Armor Header line is placed somewh
ere in the body.
And, very large Cleartext Signature Framework messages cannot be processed in a
single pass, since the signature salt and digest algorithms are only discovered
at the end.</t>
<t>An implementation that knows it is working with a textual stream with
any of the above characteristics <bcp14>SHOULD NOT</bcp14> use the Cleartext Si
gnature Framework.
Safe alternatives for a semantically meaningful OpenPGP signature over such a fi
le format are:</t>
<ul spacing="normal">
<li>
<t>A signed message, as described in <xref target="openpgp-messages"
/>.</t>
</li>
<li>
<t>A detached signature, as described in <xref target="detached-sign
atures"/>.</t>
</li>
</ul>
<t>Either of these alternatives may be ASCII-armored (see <xref target="
forming-ascii-armor"/>) if they need to be transmitted across a text-only (or 7-
bit clean) channel.</t>
<t>Finally, when a Cleartext Signature Framework message is presented to
the user as is, an attacker can include additional text in the <tt>Hash</tt> he
ader, which may mislead the user into thinking it is part of the signed text.
The signature validation constraints described in Sections <xref target="armor-h
eader-key-hash" format="counter"/> and <xref target="cleartext-structure" format
="counter"/> help to mitigate the risk of arbitrary or misleading text in the Ar
mor Headers.</t>
</section>
</section>
</section> <section anchor="regular-expressions">
<section anchor="dash-escaping"><name>Dash-Escaped Text</name> <name>Regular Expressions</name>
<t>This section describes Regular Expressions.</t>
<t>The cleartext content of the message must also be dash-escaped.</t>
<t>Dash-escaped cleartext is the ordinary cleartext where every line starting wi
th a <u>-</u> is prefixed by the sequence <u>-</u> and <u> </u>.
This prevents the parser from recognizing armor headers of the cleartext itself.
An implementation <bcp14>MAY</bcp14> dash-escape any line, <bcp14>SHOULD</bcp14>
dash-escape lines commencing "From" followed by a space, and <bcp14>MUST</bcp14
> dash-escape any line commencing in a dash.
The message digest is computed using the cleartext itself, not the dash-escaped
form.</t>
<t>When reversing dash-escaping, an implementation <bcp14>MUST</bcp14> strip the
string <spanx style="verb">- </spanx> if it occurs at the beginning of a line,
and <bcp14>SHOULD</bcp14> warn on <spanx style="verb">-</spanx> and any characte
r other than a space at the beginning of a line.</t>
</section>
<section anchor="csf-issues"><name>Issues with the Cleartext Signature Framework
</name>
<t>Since creating a cleartext signed message involves trimming trailing whitespa <dl>
ce on every line, the Cleartext Signature Framework will fail to safely round-tr <dt>Regular Expression:</dt><dd>Zero or more branches, separated by <tt>|<
ip any textual stream that may include semantically meaningful whitespace.</t> /tt>.
It matches anything that matches one of the branches.</dd>
<dt>Branch:</dt><dd>Zero or more pieces, concatenated. It matches a match
for the first, followed by a match for the second, etc.</dd>
<dt>Piece:</dt><dd>An atom possibly followed by <tt>*</tt>, <tt>+</tt>, or
<tt>?</tt>.
An atom followed by <tt>*</tt> matches a sequence of 0 or more matches of the at
om.
An atom followed by <tt>+</tt> matches a sequence of 1 or more matches of the at
om.
An atom followed by <tt>?</tt> matches a match of the atom or the null string.</
dd>
<dt>Atom:</dt><dd>A Regular Expression in parentheses (matching a match fo
r the Regular Expression), a range (see below), a <tt>.</tt> (matching any singl
e Unicode character), a <tt>^</tt> (matching the null string at the beginning of
the input string), a <tt>$</tt> (matching the null string at the end of the inp
ut string), a <tt>\</tt> followed by a single Unicode character (matching that c
haracter), or a single Unicode character with no other significance (matching th
at character).</dd>
<dt>Range:</dt><dd>A sequence of characters enclosed in <tt>[]</tt>.
It normally matches any single character from the sequence.
If the sequence begins with <tt>^</tt>, it matches any single Unicode character
not from the rest of the sequence. If two characters in the sequence are separat
ed by <tt>-</tt>, this is shorthand for the full list of Unicode characters betw
een them in codepoint order (for example, <tt>[0-9]</tt> matches any decimal dig
it). To include a literal <tt>]</tt> in the sequence, make it the first characte
r (following a possible <tt>^</tt>). To include a literal <tt>-</tt>, make it th
e first or last character.</dd>
</dl>
</section>
<section anchor="constants">
<name>Constants</name>
<t>This section describes the constants used in OpenPGP.</t>
<t>Note that these tables are not exhaustive lists; an implementation <bcp
14>MAY</bcp14> implement an algorithm that is not on these lists, as long as the
algorithm IDs are chosen from the Private or Experimental Use algorithm range.<
/t>
<t>See <xref target="notes-on-algorithms"/> for more discussion of the alg
orithms.</t>
<section anchor="pubkey-algos">
<name>Public Key Algorithms</name>
<table anchor="pubkey-algo-registry">
<name>OpenPGP Public Key Algorithms Registry</name>
<thead>
<tr>
<th align="right">ID</th>
<th align="left">Algorithm</th>
<th align="left">Public Key Format</th>
<th align="left">Secret Key Format</th>
<th align="left">Signature Format</th>
<th align="left">PKESK Format</th>
</tr>
</thead>
<tbody>
<tr>
<td align="right">0</td>
<td align="left">Reserved</td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
</tr>
<tr>
<td align="right">1</td>
<td align="left">RSA (Encrypt or Sign) <xref target="FIPS186"/></t
d>
<td align="left">MPI(n), MPI(e) [<xref target="key-rsa"/>]</td>
<td align="left">MPI(d), MPI(p), MPI(q), MPI(u)</td>
<td align="left">MPI(m<sup>d</sup> mod n) [<xref target="sig-rsa"/
>]</td>
<td align="left">MPI(m<sup>e</sup> mod n) [<xref target="pkesk-rsa
"/>]</td>
</tr>
<tr>
<td align="right">2</td>
<td align="left">RSA Encrypt-Only <xref target="FIPS186"/></td>
<td align="left">MPI(n), MPI(e) [<xref target="key-rsa"/>]</td>
<td align="left">MPI(d), MPI(p), MPI(q), MPI(u)</td>
<td align="left">N/A</td>
<td align="left">MPI(m<sup>e</sup> mod n) [<xref target="pkesk-rsa
"/>]</td>
</tr>
<tr>
<td align="right">3</td>
<td align="left">RSA Sign-Only <xref target="FIPS186"/></td>
<td align="left">MPI(n), MPI(e) [<xref target="key-rsa"/>]</td>
<td align="left">MPI(d), MPI(p), MPI(q), MPI(u)</td>
<td align="left">MPI(m<sup>d</sup> mod n) [<xref target="sig-rsa"/
>]</td>
<td align="left">N/A</td>
</tr>
<tr>
<td align="right">16</td>
<td align="left">Elgamal (Encrypt-Only) <xref target="ELGAMAL"/></
td>
<td align="left">MPI(p), MPI(g), MPI(y) [<xref target="key-elgamal
"/>]</td>
<td align="left">MPI(x)</td>
<td align="left">N/A</td>
<td align="left">MPI(g<sup>k</sup> mod p), MPI(m * y<sup>k</sup> m
od p) [<xref target="pkesk-elgamal"/>]</td>
</tr>
<tr>
<td align="right">17</td>
<td align="left">DSA (Digital Signature Algorithm) <xref target="F
IPS186"/></td>
<td align="left">MPI(p), MPI(q), MPI(g), MPI(y) [<xref target="key
-dsa"/>]</td>
<td align="left">MPI(x)</td>
<td align="left">MPI(r), MPI(s) [<xref target="sig-dsa"/>]</td>
<td align="left">N/A</td>
</tr>
<tr>
<td align="right">18</td>
<td align="left">ECDH public key algorithm</td>
<td align="left">OID, MPI(point in curve-specific point format), K
DFParams [Sections <xref target="curve-specific-formats" format="counter"/> and
<xref target="key-ecdh" format="counter"/>]</td>
<td align="left">MPI(value in curve-specific format) [<xref target
="curve-specific-formats"/>]</td>
<td align="left">N/A</td>
<td align="left">MPI(point in curve-specific point format), size o
ctet, encoded key [Sections <xref target="curve-specific-formats" format="counte
r"/>, <xref target="pkesk-ecdh" format="counter"/>, and <xref target="ecdh" form
at="counter"/>]</td>
</tr>
<tr>
<td align="right">19</td>
<td align="left">ECDSA public key algorithm <xref target="FIPS186"
/></td>
<td align="left">OID, MPI(point in SEC1 format) [<xref target="key
-ecdsa"/>]</td>
<td align="left">MPI(value)</td>
<td align="left">MPI(r), MPI(s) [<xref target="sig-dsa"/>]</td>
<td align="left">N/A</td>
</tr>
<tr>
<td align="right">20</td>
<td align="left">Reserved (formerly Elgamal Encrypt or Sign)</td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
</tr>
<tr>
<td align="right">21</td>
<td align="left">Reserved for Diffie-Hellman (X9.42, as defined fo
r IETF-S/MIME)</td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
</tr>
<tr>
<td align="right">22</td>
<td align="left">EdDSALegacy (deprecated)</td>
<td align="left">OID, MPI(point in prefixed native format) [Sectio
ns <xref target="ec-point-prefixed-native" format="counter"/> and <xref target="
key-eddsa-legacy" format="counter"/>]</td>
<td align="left">MPI(value in curve-specific format) [<xref target
="curve-specific-formats"/>]</td>
<td align="left">MPI, MPI [Sections <xref target="curve-specific-f
ormats" format="counter"/> and <xref target="sig-eddsa-legacy" format="counter"/
>]</td>
<td align="left">N/A</td>
</tr>
<tr>
<td align="right">23</td>
<td align="left">Reserved (AEDH)</td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
</tr>
<tr>
<td align="right">24</td>
<td align="left">Reserved (AEDSA)</td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
</tr>
<tr>
<td align="right">25</td>
<td align="left">X25519</td>
<td align="left">32 octets [<xref target="key-x25519"/>]</td>
<td align="left">32 octets</td>
<td align="left">N/A</td>
<td align="left">32 octets, size octet, encoded key [<xref target=
"pkesk-x25519"/>]</td>
</tr>
<tr>
<td align="right">26</td>
<td align="left">X448</td>
<td align="left">56 octets [<xref target="key-x448"/>]</td>
<td align="left">56 octets</td>
<td align="left">N/A</td>
<td align="left">56 octets, size octet, encoded key [<xref target=
"pkesk-x448"/>]</td>
</tr>
<tr>
<td align="right">27</td>
<td align="left">Ed25519</td>
<td align="left">32 octets [<xref target="key-ed25519"/>]</td>
<td align="left">32 octets</td>
<td align="left">64 octets [<xref target="sig-ed25519"/>]</td>
<td align="left"> </td>
</tr>
<tr>
<td align="right">28</td>
<td align="left">Ed448</td>
<td align="left">57 octets [<xref target="key-ed448"/>]</td>
<td align="left">57 octets</td>
<td align="left">114 octets [<xref target="sig-ed448"/>]</td>
<td align="left"> </td>
</tr>
<tr>
<td align="right">100 to 110</td>
<td align="left">Private or Experimental Use</td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
<td align="left"> </td>
</tr>
</tbody>
</table>
<t>For example, the Unified Diff format <xref target="UNIFIED-DIFF"/> contains s <t>Implementations <bcp14>MUST</bcp14> implement Ed25519 (27) for signat
emantically meaningful whitespace: an empty line of context will consist of a li ures and X25519 (25) for encryption.
ne with a single <u> </u> character, and any line that has trailing whitespace a Implementations <bcp14>SHOULD</bcp14> implement Ed448 (28) and X448 (26).</t>
dded or removed will represent such a change with semantically meaningful whites <t>RSA (1) keys are deprecated and <bcp14>SHOULD NOT</bcp14> be generate
pace.</t> d but may be interpreted.
RSA Encrypt-Only (2) and RSA Sign-Only (3) are deprecated and <bcp14>MUST NOT</b
cp14> be generated (see <xref target="rsa-notes"/>). Elgamal (16) keys are depre
cated and <bcp14>MUST NOT</bcp14> be generated (see <xref target="elgamal-notes"
/>). DSA (17) keys are deprecated and <bcp14>MUST NOT</bcp14> be generated (see
<xref target="dsa-notes"/>). For notes on Elgamal Encrypt or Sign (20) and X9.42
(21), see <xref target="reserved-notes"/>.
Implementations <bcp14>MAY</bcp14> implement any other algorithm.</t>
<t>Note that an implementation conforming to the previous version of thi
s specification <xref target="RFC4880"/> has only DSA (17) and Elgamal (16) as t
he algorithms that <bcp14>MUST</bcp14> be implemented.</t>
<t>A compatible specification of ECDSA is given in <xref target="RFC6090
"/> (as "KT-I Signatures") and in <xref target="SEC1"/>; ECDH is defined in <xre
f target="ecdh"/> of this document.</t>
</section>
<section anchor="ec-curves">
<name>ECC Curves for OpenPGP</name>
<t>The parameter curve OID is an array of octets that defines a named cu
rve.</t>
<t>The table below specifies the exact sequence of octets for each named
curve referenced in this document. It also specifies which public key algorithm
s the curve can be used with, as well as the size of expected elements in octets
. Note that there is a break in "EdDSALegacy" for display purposes only.</t>
<t>Furthermore, a Cleartext Signature Framework message that is very large is un <table anchor="ecc-oid-usage-registry">
likely to work well. <name>OpenPGP ECC Curve OIDs and Usage Registry</name>
In particular, it will be difficult for any human reading the message to know wh <thead>
ich part of the message is covered by the signature because they can't understan <tr>
d the whole message at once, in case an Armor Header line is placed somewhere in <th align="left">ASN.1 Object Identifier</th>
the body. <th align="left">OID Len</th>
And, very large Cleartext Signature Framework messages cannot be processed in a <th align="left">Curve OID Octets</th>
single pass, since the signature salt and digest algorithms are only discovered <th align="left">Curve Name</th>
at the end.</t> <th align="left">Usage</th>
<th align="left">Field Size (fsize)</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">1.2.840.10045.3.1.7</td>
<td align="left">8</td>
<td align="left">2A 86 48 CE 3D 03 01 07</td>
<td align="left">NIST P-256</td>
<td align="left">ECDSA, ECDH</td>
<td align="left">32</td>
</tr>
<tr>
<td align="left">1.3.132.0.34</td>
<td align="left">5</td>
<td align="left">2B 81 04 00 22</td>
<td align="left">NIST P-384</td>
<td align="left">ECDSA, ECDH</td>
<td align="left">48</td>
</tr>
<tr>
<td align="left">1.3.132.0.35</td>
<td align="left">5</td>
<td align="left">2B 81 04 00 23</td>
<td align="left">NIST P-521</td>
<td align="left">ECDSA, ECDH</td>
<td align="left">66</td>
</tr>
<tr>
<td align="left">1.3.36.3.3.2.8.1.1.7</td>
<td align="left">9</td>
<td align="left">2B 24 03 03 02 08 01 01 07</td>
<td align="left">brainpoolP256r1</td>
<td align="left">ECDSA, ECDH</td>
<td align="left">32</td>
</tr>
<tr>
<td align="left">1.3.36.3.3.2.8.1.1.11</td>
<td align="left">9</td>
<td align="left">2B 24 03 03 02 08 01 01 0B</td>
<td align="left">brainpoolP384r1</td>
<td align="left">ECDSA, ECDH</td>
<td align="left">48</td>
</tr>
<tr>
<td align="left">1.3.36.3.3.2.8.1.1.13</td>
<td align="left">9</td>
<td align="left">2B 24 03 03 02 08 01 01 0D</td>
<td align="left">brainpoolP512r1</td>
<td align="left">ECDSA, ECDH</td>
<td align="left">64</td>
</tr>
<tr>
<td align="left">1.3.6.1.4.1.11591.15.1</td>
<td align="left">9</td>
<td align="left">2B 06 01 04 01 DA 47 0F 01</td>
<td align="left">Ed25519Legacy</td>
<td align="left">EdDSA<br/>Legacy</td>
<td align="left">32</td>
</tr>
<tr>
<td align="left">1.3.6.1.4.1.3029.1.5.1</td>
<td align="left">10</td>
<td align="left">2B 06 01 04 01 97 55 01 05 01</td>
<td align="left">Curve25519Legacy</td>
<td align="left">ECDH</td>
<td align="left">32</td>
</tr>
</tbody>
</table>
<t>An implementation that knows it is working with a textual stream with any of <t>The "Field Size (fsize)" column represents the field size of the grou
the above characteristics <bcp14>SHOULD NOT</bcp14> use the Cleartext Signature p in number of octets, rounded up, such that x or y coordinates for a point on t
Framework. he curve or native point representations for the curve can be represented in tha
Safe alternatives for a semantically meaningful OpenPGP signature over such a fi t many octets. The curves specified here, and scalars such as the base point ord
le format are:</t> er and the private key, can be represented in fsize octets. However, note that c
urves exist outside this specification where the representation of scalars requi
res an additional octet.</t>
<t>The sequence of octets in the third column is the result of applying
the Distinguished Encoding Rules (DER) to the ASN.1 Object Identifier with subse
quent truncation. The truncation removes the two fields of encoded Object Identi
fier. The first omitted field is 1 octet representing the Object Identifier tag,
and the second omitted field is the length of the Object Identifier body.
For example, the complete ASN.1 DER encoding for the NIST P-256 curve OID is "06
08 2A 86 48 CE 3D 03 01 07", from which the first entry in the table above is c
onstructed by omitting the first two octets.
Only the truncated sequence of octets is the valid representation of a curve OID
.</t>
<t>The deprecated OIDs for Ed25519Legacy and Curve25519Legacy are used o
nly in version 4 keys and signatures.
Implementations <bcp14>MAY</bcp14> implement these variants for compatibility wi
th existing version 4 key material and signatures.
Implementations <bcp14>MUST NOT</bcp14> accept or generate version 6 key materia
l using the deprecated OIDs.</t>
<section anchor="curve-specific-formats">
<name>Curve-Specific Wire Formats</name>
<t>Some elliptic curve public key algorithms use different conventions
for specific fields depending on the curve in use. Each field is always formatt
ed as an MPI, but with a curve-specific framing. This table summarizes those dis
tinctions.</t>
<table anchor="ecc-wire-formats-registry">
<name>OpenPGP ECC Curve-Specific Wire Formats Registry</name>
<thead>
<tr>
<th align="left">Curve</th>
<th align="left">ECDH Point Format</th>
<th align="left">ECDH Secret Key MPI</th>
<th align="left">EdDSA Secret Key MPI</th>
<th align="left">EdDSA Signature first MPI</th>
<th align="left">EdDSA Signature second MPI</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">NIST P-256</td>
<td align="left">SEC1</td>
<td align="left">integer</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
</tr>
<tr>
<td align="left">NIST P-384</td>
<td align="left">SEC1</td>
<td align="left">integer</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
</tr>
<tr>
<td align="left">NIST P-521</td>
<td align="left">SEC1</td>
<td align="left">integer</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
</tr>
<tr>
<td align="left">brainpoolP256r1</td>
<td align="left">SEC1</td>
<td align="left">integer</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
</tr>
<tr>
<td align="left">brainpoolP384r1</td>
<td align="left">SEC1</td>
<td align="left">integer</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
</tr>
<tr>
<td align="left">brainpoolP512r1</td>
<td align="left">SEC1</td>
<td align="left">integer</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
</tr>
<tr>
<td align="left">Ed25519Legacy</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
<td align="left">32 octets of secret</td>
<td align="left">32 octets of R</td>
<td align="left">32 octets of S</td>
</tr>
<tr>
<td align="left">Curve25519Legacy</td>
<td align="left">prefixed native</td>
<td align="left">integer (<xref target="curve25519-secrets"/>)</
td>
<td align="left">N/A</td>
<td align="left">N/A</td>
<td align="left">N/A</td>
</tr>
</tbody>
</table>
<t>For the native octet-string forms of Ed25519Legacy values, see <xre
f target="RFC8032"/>.
For the native octet-string forms of Curve25519Legacy secret scalars and points,
see <xref target="RFC7748"/>.</t>
</section>
</section>
<section anchor="symmetric-algos">
<name>Symmetric Key Algorithms</name>
<table anchor="symkey-algorithms-registry">
<name>OpenPGP Symmetric Key Algorithms Registry</name>
<thead>
<tr>
<th align="right">ID</th>
<th align="left">Algorithm</th>
<t><list style="symbols"> </tr>
<t>A Signed Message, as described in <xref target="openpgp-messages"/>.</t> </thead>
<t>A Detached Signature as described in <xref target="detached-signatures"/>.< <tbody>
/t> <tr>
</list></t> <td align="right">0</td>
<td align="left">Plaintext or unencrypted data</td>
<t>Either of these alternatives may be ASCII-armored (see <xref target="forming- </tr>
ascii-armor"/>) if they need to be transmitted across a text-only (or 7-bit clea <tr>
n) channel.</t> <td align="right">1</td>
<td align="left">IDEA <xref target="IDEA"/></td>
<t>Finally, when a Cleartext Signature Framework message is presented to the use </tr>
r as-is, an attacker can include additional text in the <spanx style="verb">Hash <tr>
</spanx> header, which may mislead the user into thinking it is part of the sign <td align="right">2</td>
ed text. <td align="left">TripleDES (or DES-EDE) <xref target="SP800-67"/>
The signature validation constraints described in <xref target="armor-header-key with 168-bit key derived from 192</td>
-hash"/> and <xref target="cleartext-structure"/> help to mitigate the risk of a
rbitrary or misleading text in the Armor Headers.</t>
</section> </tr>
</section> <tr>
<section anchor="regular-expressions"><name>Regular Expressions</name> <td align="right">3</td>
<td align="left">CAST5 with 128-bit key <xref target="RFC2144"/></
td>
<t>A regular expression is zero or more branches, separated by <spanx style="ver </tr>
b">|</spanx>. <tr>
It matches anything that matches one of the branches.</t> <td align="right">4</td>
<td align="left">Blowfish with 128-bit key, 16 rounds <xref target
="BLOWFISH"/></td>
<t>A branch is zero or more pieces, concatenated. </tr>
It matches a match for the first, followed by a match for the second, etc.</t> <tr>
<td align="right">5</td>
<td align="left">Reserved</td>
<t>A piece is an atom possibly followed by <spanx style="verb">*</spanx>, <spanx </tr>
style="verb">+</spanx>, or <spanx style="verb">?</spanx>. <tr>
An atom followed by <spanx style="verb">*</spanx> matches a sequence of 0 or mor <td align="right">6</td>
e matches of the atom. <td align="left">Reserved</td>
An atom followed by <spanx style="verb">+</spanx> matches a sequence of 1 or mor
e matches of the atom.
An atom followed by <spanx style="verb">?</spanx> matches a match of the atom, o
r the null string.</t>
<t>An atom is a regular expression in parentheses (matching a match for the regu </tr>
lar expression), a range (see below), <spanx style="verb">.</spanx> (matching an <tr>
y single Unicode character), <spanx style="verb">^</spanx> (matching the null st <td align="right">7</td>
ring at the beginning of the input string), <spanx style="verb">$</spanx> (match <td align="left">AES with 128-bit key <xref target="AES"/></td>
ing the null string at the end of the input string), a <spanx style="verb">\</sp
anx> followed by a single Unicode character (matching that character), or a sing
le Unicode character with no other significance (matching that character).</t>
<t>A range is a sequence of characters enclosed in <spanx style="verb">[]</spanx </tr>
>. <tr>
It normally matches any single character from the sequence. <td align="right">8</td>
If the sequence begins with <spanx style="verb">^</spanx>, it matches any single <td align="left">AES with 192-bit key</td>
Unicode character not from the rest of the sequence.
If two characters in the sequence are separated by <spanx style="verb">-</spanx>
, this is shorthand for the full list of Unicode characters between them in code
point order (for example, <spanx style="verb">[0-9]</spanx> matches any decimal
digit).
To include a literal <spanx style="verb">]</spanx> in the sequence, make it the
first character (following a possible <spanx style="verb">^</spanx>).
To include a literal <spanx style="verb">-</spanx>, make it the first or last ch
aracter.</t>
</section> </tr>
<section anchor="constants"><name>Constants</name> <tr>
<td align="right">9</td>
<td align="left">AES with 256-bit key</td>
<t>This section describes the constants used in OpenPGP.</t> </tr>
<tr>
<td align="right">10</td>
<td align="left">Twofish with 256-bit key <xref target="TWOFISH"/>
</td>
<t>Note that these tables are not exhaustive lists; an implementation <bcp14>MAY </tr>
</bcp14> implement an algorithm not on these lists, so long as the algorithm IDs <tr>
are chosen from the private or experimental algorithm range.</t> <td align="right">11</td>
<td align="left">Camellia with 128-bit key <xref target="RFC3713"/
></td>
<t>See <xref target="notes-on-algorithms"/> for more discussion of the algorithm </tr>
s.</t> <tr>
<td align="right">12</td>
<td align="left">Camellia with 192-bit key</td>
<section anchor="pubkey-algos"><name>Public-Key Algorithms</name> </tr>
<tr>
<td align="right">13</td>
<td align="left">Camellia with 256-bit key</td>
<texttable title="OpenPGP Public Key Algorithms registry" anchor="pubkey-algo-re </tr>
gistry"> <tr>
<ttcol align='right'>ID</ttcol> <td align="right">100-110</td>
<ttcol align='left'>Algorithm</ttcol> <td align="left">Private or Experimental Use</td>
<ttcol align='left'>Public Key Format</ttcol>
<ttcol align='left'>Secret Key Format</ttcol>
<ttcol align='left'>Signature Format</ttcol>
<ttcol align='left'>PKESK Format</ttcol>
<c>0</c>
<c>Reserved</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
<c>1</c>
<c>RSA (Encrypt or Sign) <xref target="FIPS186"/></c>
<c>MPI(n), MPI(e) [<xref target="key-rsa"/>]</c>
<c>MPI(d), MPI(p), MPI(q), MPI(u)</c>
<c>MPI(m**d mod n) [<xref target="sig-rsa"/>]</c>
<c>MPI(m**e mod n) [<xref target="pkesk-rsa"/>]</c>
<c>2</c>
<c>RSA Encrypt-Only <xref target="FIPS186"/></c>
<c>MPI(n), MPI(e) [<xref target="key-rsa"/>]</c>
<c>MPI(d), MPI(p), MPI(q), MPI(u)</c>
<c>N/A</c>
<c>MPI(m**e mod n) [<xref target="pkesk-rsa"/>]</c>
<c>3</c>
<c>RSA Sign-Only <xref target="FIPS186"/></c>
<c>MPI(n), MPI(e) [<xref target="key-rsa"/>]</c>
<c>MPI(d), MPI(p), MPI(q), MPI(u)</c>
<c>MPI(m**d mod n) [<xref target="sig-rsa"/>]</c>
<c>N/A</c>
<c>16</c>
<c>Elgamal (Encrypt-Only) <xref target="ELGAMAL"/></c>
<c>MPI(p), MPI(g), MPI(y) [<xref target="key-elgamal"/>]</c>
<c>MPI(x)</c>
<c>N/A</c>
<c>MPI(g**k mod p), MPI (m * y**k mod p) [<xref target="pkesk-elgamal"/>]<
/c>
<c>17</c>
<c>DSA (Digital Signature Algorithm) <xref target="FIPS186"/></c>
<c>MPI(p), MPI(q), MPI(g), MPI(y) [<xref target="key-dsa"/>]</c>
<c>MPI(x)</c>
<c>MPI(r), MPI(s) [<xref target="sig-dsa"/>]</c>
<c>N/A</c>
<c>18</c>
<c>ECDH public key algorithm</c>
<c>OID, MPI(point in curve-specific point format), KDFParams [see <xref ta
rget="curve-specific-formats"/>, <xref target="key-ecdh"/>]</c>
<c>MPI(value in curve-specific format) [<xref target="curve-specific-forma
ts"/>]</c>
<c>N/A</c>
<c>MPI(point in curve-specific point format), size octet, encoded key [<xr
ef target="curve-specific-formats"/>, <xref target="pkesk-ecdh"/>, <xref target=
"ecdh"/>]</c>
<c>19</c>
<c>ECDSA public key algorithm <xref target="FIPS186"/></c>
<c>OID, MPI(point in SEC1 format) [<xref target="key-ecdsa"/>]</c>
<c>MPI(value)</c>
<c>MPI(r), MPI(s) [<xref target="sig-dsa"/>]</c>
<c>N/A</c>
<c>20</c>
<c>Reserved (formerly Elgamal Encrypt or Sign)</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
<c>21</c>
<c>Reserved for Diffie-Hellman (X9.42, as defined for IETF-S/MIME)</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
<c>22</c>
<c>EdDSALegacy (deprecated)</c>
<c>OID, MPI(point in prefixed native format) [see <xref target="ec-point-p
refixed-native"/>, <xref target="key-eddsa-legacy"/>]</c>
<c>MPI(value in curve-specific format) [see <xref target="curve-specific-f
ormats"/>]</c>
<c>MPI, MPI [see <xref target="curve-specific-formats"/>, <xref target="si
g-eddsa-legacy"/>]</c>
<c>N/A</c>
<c>23</c>
<c>Reserved (AEDH)</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
<c>24</c>
<c>Reserved (AEDSA)</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
<c>25</c>
<c>X25519</c>
<c>32 octets [see <xref target="key-x25519"/>]</c>
<c>32 octets</c>
<c>N/A</c>
<c>32 octets, size octet, encoded key [see <xref target="pkesk-x25519"/>]<
/c>
<c>26</c>
<c>X448</c>
<c>56 octets [see <xref target="key-x448"/>]</c>
<c>56 octets</c>
<c>N/A</c>
<c>56 octets, size octet, encoded key [see <xref target="pkesk-x448"/>]</c
>
<c>27</c>
<c>Ed25519</c>
<c>32 octets [see <xref target="key-ed25519"/>]</c>
<c>32 octets</c>
<c>64 octets [see <xref target="sig-ed25519"/>]</c>
<c>&#160;</c>
<c>28</c>
<c>Ed448</c>
<c>57 octets [see <xref target="key-ed448"/>]</c>
<c>57 octets</c>
<c>114 octets [see <xref target="sig-ed448"/>]</c>
<c>&#160;</c>
<c>100 to 110</c>
<c>Private/Experimental algorithm</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
</texttable>
<t>Implementations <bcp14>MUST</bcp14> implement Ed25519 (27) for signatures, an </tr>
d X25519 (25) for encryption. <tr>
Implementations <bcp14>SHOULD</bcp14> implement Ed448 (28) and X448 (26).</t> <td align="right">253-255</td>
<td align="left">Reserved to avoid collision with Secret Key Encry
ption (<xref target="secret-key-protection-registry"/> and <xref target="secret-
key-packet-formats"/>)</td>
<t>RSA (1) keys are deprecated and <bcp14>SHOULD NOT</bcp14> be generated, but m </tr>
ay be interpreted. </tbody>
RSA Encrypt-Only (2) and RSA Sign-Only (3) are deprecated and <bcp14>MUST NOT</b </table>
cp14> be generated. <t>Implementations <bcp14>MUST</bcp14> implement AES-128.
See <xref target="rsa-notes"/>. Implementations <bcp14>SHOULD</bcp14> implement AES-256.
Elgamal (16) keys are deprecated and <bcp14>MUST NOT</bcp14> be generated (see < Implementations <bcp14>MUST NOT</bcp14> encrypt data with IDEA, TripleDES, or CA
xref target="elgamal-notes"/>). ST5.
DSA (17) keys are deprecated and <bcp14>MUST NOT</bcp14> be generated (see <xref Implementations <bcp14>MAY</bcp14> decrypt data that uses IDEA, TripleDES, or CA
target="dsa-notes"/>). ST5 for the sake of reading older messages or new messages from implementations
See <xref target="reserved-notes"/> for notes on Elgamal Encrypt or Sign (20), a predating support for <xref target="RFC2440"/>.
nd X9.42 (21). An Implementation that decrypts data using IDEA, TripleDES, or CAST5 <bcp14>SHOU
LD</bcp14> generate a deprecation warning about the symmetric algorithm, indicat
ing that message confidentiality is suspect.
Implementations <bcp14>MAY</bcp14> implement any other algorithm.</t> Implementations <bcp14>MAY</bcp14> implement any other algorithm.</t>
</section>
<section anchor="compression-algos">
<name>Compression Algorithms</name>
<table anchor="compression-algorithms-registry">
<name>OpenPGP Compression Algorithms Registry</name>
<thead>
<tr>
<th align="right">ID</th>
<th align="left">Algorithm</th>
<t>Note that an implementation conforming to the previous version of this standa </tr>
rd (<xref target="RFC4880"/>) has only DSA (17) and Elgamal (16) as its <bcp14>M </thead>
UST</bcp14>-implement algorithms.</t> <tbody>
<tr>
<td align="right">0</td>
<td align="left">Uncompressed</td>
<t>A compatible specification of ECDSA is given in <xref target="RFC6090"/> as " </tr>
KT-I Signatures" and in <xref target="SEC1"/>; ECDH is defined in <xref target=" <tr>
ecdh"/> of this document.</t> <td align="right">1</td>
<td align="left">ZIP <xref target="RFC1951"/></td>
</section> </tr>
<section anchor="ec-curves"><name>ECC Curves for OpenPGP</name> <tr>
<td align="right">2</td>
<td align="left">ZLIB <xref target="RFC1950"/></td>
<t>The parameter curve OID is an array of octets that defines a named curve.</t> </tr>
<tr>
<td align="right">3</td>
<td align="left">BZip2 <xref target="BZ2"/></td>
<t>The table below specifies the exact sequence of octets for each named curve r </tr>
eferenced in this document. <tr>
It also specifies which public key algorithms the curve can be used with, as wel <td align="right">100-110</td>
l as the size of expected elements in octets:</t> <td align="left">Private or Experimental Use</td>
<texttable title="OpenPGP ECC Curve OID and Usage registry" anchor="ecc-oid-usag </tr>
e-registry"> </tbody>
<ttcol align='left'>ASN.1 Object Identifier</ttcol> </table>
<ttcol align='left'>OID len</ttcol> <t>Implementations <bcp14>MUST</bcp14> implement uncompressed data.
<ttcol align='left'>Curve OID octets in hex</ttcol> Implementations <bcp14>SHOULD</bcp14> implement ZLIB.
<ttcol align='left'>Curve name</ttcol> For interoperability reasons, implementations <bcp14>SHOULD</bcp14> be able to d
<ttcol align='left'>Usage</ttcol> ecompress using ZIP.
<ttcol align='left'>Field Size (fsize)</ttcol> Implementations <bcp14>MAY</bcp14> implement any other algorithm.</t>
<c>1.2.840.10045.3.1.7</c> </section>
<c>8</c> <section anchor="hash-algos">
<c>2A 86 48 CE 3D 03 01 07</c> <name>Hash Algorithms</name>
<c>NIST P-256</c> <table anchor="hash-algorithms-registry">
<c>ECDSA, ECDH</c> <name>OpenPGP Hash Algorithms Registry</name>
<c>32</c> <thead>
<c>1.3.132.0.34</c> <tr>
<c>5</c> <th align="right">ID</th>
<c>2B 81 04 00 22</c> <th align="left">Algorithm</th>
<c>NIST P-384</c> <th align="left">Text Name</th>
<c>ECDSA, ECDH</c> <th align="left">V6 Signature Salt Size</th>
<c>48</c>
<c>1.3.132.0.35</c>
<c>5</c>
<c>2B 81 04 00 23</c>
<c>NIST P-521</c>
<c>ECDSA, ECDH</c>
<c>66</c>
<c>1.3.36.3.3.2.8.1.1.7</c>
<c>9</c>
<c>2B 24 03 03 02 08 01 01 07</c>
<c>brainpoolP256r1</c>
<c>ECDSA, ECDH</c>
<c>32</c>
<c>1.3.36.3.3.2.8.1.1.11</c>
<c>9</c>
<c>2B 24 03 03 02 08 01 01 0B</c>
<c>brainpoolP384r1</c>
<c>ECDSA, ECDH</c>
<c>48</c>
<c>1.3.36.3.3.2.8.1.1.13</c>
<c>9</c>
<c>2B 24 03 03 02 08 01 01 0D</c>
<c>brainpoolP512r1</c>
<c>ECDSA, ECDH</c>
<c>64</c>
<c>1.3.6.1.4.1.11591.15.1</c>
<c>9</c>
<c>2B 06 01 04 01 DA 47 0F 01</c>
<c>Ed25519Legacy</c>
<c>EdDSALegacy</c>
<c>32</c>
<c>1.3.6.1.4.1.3029.1.5.1</c>
<c>10</c>
<c>2B 06 01 04 01 97 55 01 05 01</c>
<c>Curve25519Legacy</c>
<c>ECDH</c>
<c>32</c>
</texttable>
<t>The "Field Size (fsize)" column represents the field size of the group in num </tr>
ber of octets, rounded up, such that x or y coordinates for a point on the curve </thead>
or native point representations for the curve can be represented in that many o <tbody>
ctets. <tr>
For the curves specified here, also scalars such as the base point order and the <td align="right">0</td>
private key can be represented in fsize octets. <td align="left">Reserved</td>
Note that, however, there exist curves outside this specification where the repr <td align="left"></td>
esentation of scalars requires an additional octet.</t> <td align="left"></td>
<t>The sequence of octets in the third column is the result of applying the Dist </tr>
inguished Encoding Rules (DER) to the ASN.1 Object Identifier with subsequent tr <tr>
uncation. <td align="right">1</td>
The truncation removes the two fields of encoded Object Identifier. <td align="left">MD5 <xref target="RFC1321"/></td>
The first omitted field is one octet representing the Object Identifier tag, and <td align="left">"MD5"</td>
the second omitted field is the length of the Object Identifier body. <td align="left">N/A</td>
For example, the complete ASN.1 DER encoding for the NIST P-256 curve OID is "06
08 2A 86 48 CE 3D 03 01 07", from which the first entry in the table above is c
onstructed by omitting the first two octets.
Only the truncated sequence of octets is the valid representation of a curve OID
.</t>
<t>The deprecated OIDs for Ed25519Legacy and Curve25519Legacy are used only in v </tr>
ersion 4 keys and signatures. <tr>
Implementations <bcp14>MAY</bcp14> implement these variants for compatibility wi <td align="right">2</td>
th existing v4 key material and signatures. <td align="left">SHA-1 <xref target="FIPS180"/>
Implementations <bcp14>MUST NOT</bcp14> accept or generate v6 key material using <!--<xref target="sha1cd"/> --></td>
the deprecated OIDs.</t> <td align="left">"SHA1"</td>
<td align="left">N/A</td>
<section anchor="curve-specific-formats"><name>Curve-Specific Wire Formats</name </tr>
> <tr>
<td align="right">3</td>
<td align="left">RIPEMD-160 <xref target="RIPEMD-160"/></td>
<td align="left">"RIPEMD160"</td>
<td align="left">N/A</td>
<t>Some Elliptic Curve Public Key Algorithms use different conventions for speci </tr>
fic fields depending on the curve in use. <tr>
Each field is always formatted as an MPI, but with a curve-specific framing. <td align="right">4</td>
This table summarizes those distinctions.</t> <td align="left">Reserved</td>
<td align="left"> </td>
<td align="left"> </td>
<texttable title="OpenPGP ECC Curve-specific Wire Formats registry" anchor="ecc- </tr>
wire-formats-registry"> <tr>
<ttcol align='left'>Curve</ttcol> <td align="right">5</td>
<ttcol align='left'>ECDH Point Format</ttcol> <td align="left">Reserved</td>
<ttcol align='left'>ECDH Secret Key MPI</ttcol> <td align="left"> </td>
<ttcol align='left'>EdDSA Secret Key MPI</ttcol> <td align="left"> </td>
<ttcol align='left'>EdDSA Signature first MPI</ttcol>
<ttcol align='left'>EdDSA Signature second MPI</ttcol>
<c>NIST P-256</c>
<c>SEC1</c>
<c>integer</c>
<c>N/A</c>
<c>N/A</c>
<c>N/A</c>
<c>NIST P-384</c>
<c>SEC1</c>
<c>integer</c>
<c>N/A</c>
<c>N/A</c>
<c>N/A</c>
<c>NIST P-521</c>
<c>SEC1</c>
<c>integer</c>
<c>N/A</c>
<c>N/A</c>
<c>N/A</c>
<c>brainpoolP256r1</c>
<c>SEC1</c>
<c>integer</c>
<c>N/A</c>
<c>N/A</c>
<c>N/A</c>
<c>brainpoolP384r1</c>
<c>SEC1</c>
<c>integer</c>
<c>N/A</c>
<c>N/A</c>
<c>N/A</c>
<c>brainpoolP512r1</c>
<c>SEC1</c>
<c>integer</c>
<c>N/A</c>
<c>N/A</c>
<c>N/A</c>
<c>Ed25519Legacy</c>
<c>N/A</c>
<c>N/A</c>
<c>32 octets of secret</c>
<c>32 octets of R</c>
<c>32 octets of S</c>
<c>Curve25519Legacy</c>
<c>prefixed native</c>
<c>integer (see <xref target="curve25519-secrets"/>)</c>
<c>N/A</c>
<c>N/A</c>
<c>N/A</c>
</texttable>
<t>For the native octet-string forms of Ed25519Legacy values, see <xref target=" </tr>
RFC8032"/>. <tr>
For the native octet-string forms of Curve25519Legacy secret scalars and points, <td align="right">6</td>
see <xref target="RFC7748"/>.</t> <td align="left">Reserved</td>
<td align="left"> </td>
<td align="left"> </td>
</section> </tr>
</section> <tr>
<section anchor="symmetric-algos"><name>Symmetric-Key Algorithms</name> <td align="right">7</td>
<td align="left">Reserved</td>
<td align="left"> </td>
<td align="left"> </td>
<texttable title="OpenPGP Symmetric Key Algorithms registry" anchor="symkey-algo </tr>
rithms-registry"> <tr>
<ttcol align='right'>ID</ttcol> <td align="right">8</td>
<ttcol align='left'>Algorithm</ttcol> <td align="left">SHA2-256 <xref target="FIPS180"/></td>
<c>0</c> <td align="left">"SHA256"</td>
<c>Plaintext or unencrypted data</c> <td align="left">16</td>
<c>1</c>
<c>IDEA <xref target="IDEA"/></c>
<c>2</c>
<c>TripleDES (DES-EDE, <xref target="SP800-67"/> - 168 bit key derived fro
m 192)</c>
<c>3</c>
<c>CAST5 (128 bit key, as per <xref target="RFC2144"/>)</c>
<c>4</c>
<c>Blowfish (128 bit key, 16 rounds) <xref target="BLOWFISH"/></c>
<c>5</c>
<c>Reserved</c>
<c>6</c>
<c>Reserved</c>
<c>7</c>
<c>AES with 128-bit key <xref target="AES"/></c>
<c>8</c>
<c>AES with 192-bit key</c>
<c>9</c>
<c>AES with 256-bit key</c>
<c>10</c>
<c>Twofish with 256-bit key <xref target="TWOFISH"/></c>
<c>11</c>
<c>Camellia with 128-bit key <xref target="RFC3713"/></c>
<c>12</c>
<c>Camellia with 192-bit key</c>
<c>13</c>
<c>Camellia with 256-bit key</c>
<c>100 to 110</c>
<c>Private/Experimental algorithm</c>
<c>253, 254 and 255</c>
<c>Reserved to avoid collision with Secret Key Encryption (see <xref targe
t="secret-key-protection-registry"/> and <xref target="secret-key-packet-formats
"/>)</c>
</texttable>
<t>Implementations <bcp14>MUST</bcp14> implement AES-128. </tr>
Implementations <bcp14>SHOULD</bcp14> implement AES-256. <tr>
Implementations <bcp14>MUST NOT</bcp14> encrypt data with IDEA, TripleDES, or CA <td align="right">9</td>
ST5. <td align="left">SHA2-384 <xref target="FIPS180"/></td>
Implementations <bcp14>MAY</bcp14> decrypt data that uses IDEA, TripleDES, or CA <td align="left">"SHA384"</td>
ST5 for the sake of reading older messages or new messages from implementations <td align="left">24</td>
predating support for <xref target="RFC2440"/>.
An Implementation that decrypts data using IDEA, TripleDES, or CAST5 <bcp14>SHOU
LD</bcp14> generate a deprecation warning about the symmetric algorithm, indicat
ing that message confidentiality is suspect.
Implementations <bcp14>MAY</bcp14> implement any other algorithm.</t>
</section> </tr>
<section anchor="compression-algos"><name>Compression Algorithms</name> <tr>
<td align="right">10</td>
<td align="left">SHA2-512 <xref target="FIPS180"/></td>
<td align="left">"SHA512"</td>
<td align="left">32</td>
<texttable title="OpenPGP Compression Algorithms registry" anchor="compression-a </tr>
lgorithms-registry"> <tr>
<ttcol align='right'>ID</ttcol> <td align="right">11</td>
<ttcol align='left'>Algorithm</ttcol> <td align="left">SHA2-224 <xref target="FIPS180"/></td>
<c>0</c> <td align="left">"SHA224"</td>
<c>Uncompressed</c> <td align="left">16</td>
<c>1</c>
<c>ZIP <xref target="RFC1951"/></c>
<c>2</c>
<c>ZLIB <xref target="RFC1950"/></c>
<c>3</c>
<c>BZip2 <xref target="BZ2"/></c>
<c>100 to 110</c>
<c>Private/Experimental algorithm</c>
</texttable>
<t>Implementations <bcp14>MUST</bcp14> implement uncompressed data. </tr>
Implementations <bcp14>SHOULD</bcp14> implement ZLIB. <tr>
For interoperability reasons implementations <bcp14>SHOULD</bcp14> be able to de <td align="right">12</td>
compress using ZIP. <td align="left">SHA3-256 <xref target="FIPS202"/></td>
Implementations <bcp14>MAY</bcp14> implement any other algorithm.</t> <td align="left">"SHA3-256"</td>
<td align="left">16</td>
</section> </tr>
<section anchor="hash-algos"><name>Hash Algorithms</name> <tr>
<td align="right">13</td>
<td align="left">Reserved</td>
<td align="left"> </td>
<td align="left"> </td>
<texttable title="OpenPGP Hash Algorithms registry" anchor="hash-algorithms-regi </tr>
stry"> <tr>
<ttcol align='right'>ID</ttcol> <td align="right">14</td>
<ttcol align='left'>Algorithm</ttcol> <td align="left">SHA3-512 <xref target="FIPS202"/></td>
<ttcol align='left'>Text Name</ttcol> <td align="left">"SHA3-512"</td>
<ttcol align='left'>V6 signature salt size</ttcol> <td align="left">32</td>
<c>1</c>
<c>MD5 <xref target="RFC1321"/></c>
<c>"MD5"</c>
<c>N/A</c>
<c>2</c>
<c>SHA-1 <xref target="FIPS180"/>, <xref target="sha1cd"/></c>
<c>"SHA1"</c>
<c>N/A</c>
<c>3</c>
<c>RIPEMD-160 <xref target="RIPEMD-160"/></c>
<c>"RIPEMD160"</c>
<c>N/A</c>
<c>4</c>
<c>Reserved</c>
<c>&#160;</c>
<c>&#160;</c>
<c>5</c>
<c>Reserved</c>
<c>&#160;</c>
<c>&#160;</c>
<c>6</c>
<c>Reserved</c>
<c>&#160;</c>
<c>&#160;</c>
<c>7</c>
<c>Reserved</c>
<c>&#160;</c>
<c>&#160;</c>
<c>8</c>
<c>SHA2-256 <xref target="FIPS180"/></c>
<c>"SHA256"</c>
<c>16</c>
<c>9</c>
<c>SHA2-384 <xref target="FIPS180"/></c>
<c>"SHA384"</c>
<c>24</c>
<c>10</c>
<c>SHA2-512 <xref target="FIPS180"/></c>
<c>"SHA512"</c>
<c>32</c>
<c>11</c>
<c>SHA2-224 <xref target="FIPS180"/></c>
<c>"SHA224"</c>
<c>16</c>
<c>12</c>
<c>SHA3-256 <xref target="FIPS202"/></c>
<c>"SHA3-256"</c>
<c>16</c>
<c>13</c>
<c>Reserved</c>
<c>&#160;</c>
<c>&#160;</c>
<c>14</c>
<c>SHA3-512 <xref target="FIPS202"/></c>
<c>"SHA3-512"</c>
<c>32</c>
<c>100 to 110</c>
<c>Private/Experimental algorithm</c>
<c>&#160;</c>
<c>&#160;</c>
</texttable>
<texttable title="OpenPGP Hash Algorithm Identifiers for RSA Signatures use of E </tr>
MSA-PKCS1-v1_5 Padding registry" anchor="emsa-hash-oids-registry"> <tr>
<ttcol align='left'>Hash Algorithm</ttcol> <td align="right">100-110</td>
<ttcol align='left'>OID</ttcol> <td align="left">Private or Experimental Use</td>
<ttcol align='left'>Full hash prefix</ttcol> <td align="left"> </td>
<c>MD5</c> <td align="left"> </td>
<c>1.2.840.113549.2.5</c>
<c>0x30, 0x20, 0x30, 0x0C, 0x06, 0x08, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D,
0x02, 0x05, 0x05, 0x00, 0x04, 0x10</c>
<c>SHA-1</c>
<c>1.3.14.3.2.26</c>
<c>0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2B, 0x0E, 0x03, 0x02, 0x1A, 0x05,
0x00, 0x04, 0x14</c>
<c>RIPEMD-160</c>
<c>1.3.36.3.2.1</c>
<c>0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2B, 0x24, 0x03, 0x02, 0x01, 0x05,
0x00, 0x04, 0x14</c>
<c>SHA2-256</c>
<c>2.16.840.1.101.3.4.2.1</c>
<c>0x30, 0x31, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03,
0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20</c>
<c>SHA2-384</c>
<c>2.16.840.1.101.3.4.2.2</c>
<c>0x30, 0x41, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03,
0x04, 0x02, 0x02, 0x05, 0x00, 0x04, 0x30</c>
<c>SHA2-512</c>
<c>2.16.840.1.101.3.4.2.3</c>
<c>0x30, 0x51, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03,
0x04, 0x02, 0x03, 0x05, 0x00, 0x04, 0x40</c>
<c>SHA2-224</c>
<c>2.16.840.1.101.3.4.2.4</c>
<c>0x30, 0x2D, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03,
0x04, 0x02, 0x04, 0x05, 0x00, 0x04, 0x1C</c>
<c>SHA3-256</c>
<c>2.16.840.1.101.3.4.2.8</c>
<c>0x30, 0x31, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03,
0x04, 0x02, 0x08, 0x05, 0x00, 0x04, 0x20</c>
<c>SHA3-512</c>
<c>2.16.840.1.101.3.4.2.10</c>
<c>0x30, 0x51, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03,
0x04, 0x02, 0x0a, 0x05, 0x00, 0x04, 0x40</c>
</texttable>
<t>Implementations <bcp14>MUST</bcp14> implement SHA2-256. </tr>
</tbody>
</table>
<table anchor="emsa-hash-oids-registry">
<name>OpenPGP Hash Algorithm Identifiers for RSA Signatures' Use of EM
SA&nbhy;PKCS1&nbhy;v1_5 Padding Registry</name>
<thead>
<tr>
<th align="left">Hash Algorithm</th>
<th align="left">OID</th>
<th align="left">Full Hash Prefix</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">MD5</td>
<td align="left">1.2.840.113549.2.5</td>
<td align="left">0x30, 0x20, 0x30, 0x0C, 0x06, 0x08, 0x2A, 0x86, 0
x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, 0x05, 0x00, 0x04, 0x10</td>
</tr>
<tr>
<td align="left">SHA-1</td>
<td align="left">1.3.14.3.2.26</td>
<td align="left">0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2B, 0x0E, 0
x03, 0x02, 0x1A, 0x05, 0x00, 0x04, 0x14</td>
</tr>
<tr>
<td align="left">RIPEMD-160</td>
<td align="left">1.3.36.3.2.1</td>
<td align="left">0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2B, 0x24, 0
x03, 0x02, 0x01, 0x05, 0x00, 0x04, 0x14</td>
</tr>
<tr>
<td align="left">SHA2-256</td>
<td align="left">2.16.840.1.101.3.4.2.1</td>
<td align="left">0x30, 0x31, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0
x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20</td>
</tr>
<tr>
<td align="left">SHA2-384</td>
<td align="left">2.16.840.1.101.3.4.2.2</td>
<td align="left">0x30, 0x41, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0
x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02, 0x05, 0x00, 0x04, 0x30</td>
</tr>
<tr>
<td align="left">SHA2-512</td>
<td align="left">2.16.840.1.101.3.4.2.3</td>
<td align="left">0x30, 0x51, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0
x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, 0x05, 0x00, 0x04, 0x40</td>
</tr>
<tr>
<td align="left">SHA2-224</td>
<td align="left">2.16.840.1.101.3.4.2.4</td>
<td align="left">0x30, 0x2D, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0
x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04, 0x05, 0x00, 0x04, 0x1C</td>
</tr>
<tr>
<td align="left">SHA3-256</td>
<td align="left">2.16.840.1.101.3.4.2.8</td>
<td align="left">0x30, 0x31, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0
x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x08, 0x05, 0x00, 0x04, 0x20</td>
</tr>
<tr>
<td align="left">SHA3-512</td>
<td align="left">2.16.840.1.101.3.4.2.10</td>
<td align="left">0x30, 0x51, 0x30, 0x0D, 0x06, 0x09, 0x60, 0x86, 0
x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x0a, 0x05, 0x00, 0x04, 0x40</td>
</tr>
</tbody>
</table>
<t>Implementations <bcp14>MUST</bcp14> implement SHA2-256.
Implementations <bcp14>SHOULD</bcp14> implement SHA2-384 and SHA2-512. Implementations <bcp14>SHOULD</bcp14> implement SHA2-384 and SHA2-512.
Implementations <bcp14>MAY</bcp14> implement other algorithms. Implementations <bcp14>MAY</bcp14> implement other algorithms.
Implementations <bcp14>SHOULD NOT</bcp14> create messages which require the use of SHA-1 with the exception of computing version 4 key fingerprints and for purp oses of the Modification Detection Code (MDC) in version 1 Symmetrically Encrypt ed Integrity Protected Data packets. Implementations <bcp14>SHOULD NOT</bcp14> create messages that require the use o f SHA-1, with the exception of computing version 4 key fingerprints for purposes of the MDC in version 1 Symmetrically Encrypted and Integrity Protected Data pa ckets.
Implementations <bcp14>MUST NOT</bcp14> generate signatures with MD5, SHA-1, or RIPEMD-160. Implementations <bcp14>MUST NOT</bcp14> generate signatures with MD5, SHA-1, or RIPEMD-160.
Implementations <bcp14>MUST NOT</bcp14> use MD5, SHA-1, or RIPEMD-160 as a hash function in an ECDH KDF. Implementations <bcp14>MUST NOT</bcp14> use MD5, SHA-1, or RIPEMD-160 as a hash function in an ECDH KDF.
Implementations <bcp14>MUST NOT</bcp14> generate packets using MD5, SHA-1, or RI PEMD-160 as a hash function in an S2K KDF. Implementations <bcp14>MUST NOT</bcp14> generate packets using MD5, SHA-1, or RI PEMD-160 as a hash function in an S2K KDF.
Implementations <bcp14>MUST NOT</bcp14> decrypt a secret using MD5, SHA-1, or RI PEMD-160 as a hash function in an S2K KDF in a version 6 (or later) packet. Implementations <bcp14>MUST NOT</bcp14> decrypt a secret using MD5, SHA-1, or RI PEMD-160 as a hash function in an S2K KDF in a version 6 (or later) packet.
Implementations <bcp14>MUST NOT</bcp14> validate any recent signature that depen ds on MD5, SHA-1, or RIPEMD-160. Implementations <bcp14>MUST NOT</bcp14> validate any recent signature that depen ds on MD5, SHA-1, or RIPEMD-160.
Implementations <bcp14>SHOULD NOT</bcp14> validate any old signature that depend s on MD5, SHA-1, or RIPEMD-160 unless the signature's creation date predates kno wn weakness of the algorithm used, and the implementation is confident that the message has been in the secure custody of the user the whole time.</t> Implementations <bcp14>SHOULD NOT</bcp14> validate any old signature that depend s on MD5, SHA-1, or RIPEMD-160 unless the signature's creation date predates kno wn weakness of the algorithm used, and the implementation is confident that the message has been in the secure custody of the user the whole time.</t>
</section>
<section anchor="aead-algorithms">
<name>AEAD Algorithms</name>
<table anchor="aead-algorithms-registry">
<name>OpenPGP AEAD Algorithms Registry</name>
<thead>
<tr>
<th align="right">ID</th>
<th align="left">Name</th>
<th align="left">Nonce Length (Octets)</th>
<th align="left">Authentication Tag Length (Octets)</th>
</section> </tr>
<section anchor="aead-algorithms"><name>AEAD Algorithms</name> </thead>
<tbody>
<tr>
<td align="right">0</td>
<td align="left">Reserved</td>
<td align="left"></td>
<td align="left"></td>
<texttable title="OpenPGP AEAD Algorithms registry" anchor="aead-algorithms-regi </tr>
stry"> <tr>
<ttcol align='right'>ID</ttcol> <td align="right">1</td>
<ttcol align='left'>Name</ttcol> <td align="left">EAX <xref target="EAX"/></td>
<ttcol align='left'>Reference</ttcol> <td align="left">16</td>
<ttcol align='left'>Nonce length (octets)</ttcol> <td align="left">16</td>
<ttcol align='left'>authentication tag length (octets)</ttcol>
<c>1</c>
<c>EAX</c>
<c><xref target="EAX"/></c>
<c>16</c>
<c>16</c>
<c>2</c>
<c>OCB</c>
<c><xref target="RFC7253"/></c>
<c>15</c>
<c>16</c>
<c>3</c>
<c>GCM</c>
<c><xref target="SP800-38D"/></c>
<c>12</c>
<c>16</c>
<c>100 to 110</c>
<c>Private/Experimental algorithm</c>
<c>&#160;</c>
<c>&#160;</c>
<c>&#160;</c>
</texttable>
<t>Implementations <bcp14>MUST</bcp14> implement OCB. </tr>
Implementations <bcp14>MAY</bcp14> implement EAX, GCM and other algorithms.</t> <tr>
<td align="right">2</td>
<td align="left">OCB <xref target="RFC7253"/></td>
<td align="left">15</td>
<td align="left">16</td>
</section> </tr>
</section> <tr>
<section anchor="packet-sequence-composition"><name>Packet Sequence Composition< <td align="right">3</td>
/name> <td align="left">GCM <xref target="SP800-38D"/></td>
<td align="left">12</td>
<td align="left">16</td>
<t>OpenPGP packets are assembled into sequences in order to create messages and </tr>
to transfer keys. <tr>
<td align="right">100-110</td>
<td align="left">Private or Experimental Use</td>
<td align="left"> </td>
<td align="left"> </td>
</tr>
</tbody>
</table>
<t>Implementations <bcp14>MUST</bcp14> implement OCB. Implementations <b
cp14>MAY</bcp14> implement EAX, GCM, and other algorithms.</t>
</section>
</section>
<section anchor="packet-sequence-composition">
<name>Packet Sequence Composition</name>
<t>OpenPGP packets are assembled into sequences in order to create message
s and to transfer keys.
Not all possible packet sequences are meaningful and correct. Not all possible packet sequences are meaningful and correct.
This section describes the rules for how packets should be placed into sequences .</t> This section describes the rules for how packets should be placed into sequences .</t>
<t>There are three distinct sequences of packets:</t>
<t>There are three distinct sequences of packets:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>Transferable Public Keys (<xref target="transferable-public-keys"/>
<t>Transferable Public Keys (<xref target="transferable-public-keys"/>) and th ) and their close counterpart, Transferable Secret Keys (<xref target="transfera
eir close counterpart, Transferable Secret Keys (<xref target="transferable-secr ble-secret-keys"/>)</t>
et-keys"/>)</t> </li>
<t>OpenPGP Messages (<xref target="openpgp-messages"/>)</t> <li>
<t>Detached Signatures (<xref target="detached-signatures"/>)</t> <t>OpenPGP Messages (<xref target="openpgp-messages"/>)</t>
</list></t> </li>
<li>
<t>Each sequence has an explicit grammar of what packet types (<xref target="pac <t>Detached Signatures (<xref target="detached-signatures"/>)</t>
ket-types-registry"/>) can appear in what place. </li>
The presence of an unknown critical packet, or a known but unexpected packet is </ul>
a critical error, invalidating the entire sequence (see <xref target="packet-cri <t>Each sequence has an explicit grammar of what packet types (<xref targe
ticality"/>). t="packet-types-registry"/>) can appear in what place. The presence of an unknow
On the other hand, unknown non-critical packets can appear anywhere within any s n critical packet, or a known but unexpected packet, is a critical error, invali
equence. dating the entire sequence (see <xref target="packet-criticality"/>).
This provides a structured way to introduce new packets into the protocol, while On the other hand, unknown non-critical packets can appear anywhere within any s
making sure that certain packets will be handled strictly.</t> equence. This provides a structured way to introduce new packets into OpenPGP, w
hile making sure that certain packets will be handled strictly.</t>
<t>An implementation may "recognize" a packet, but not implement it. <t>An implementation may "recognize" a packet but not implement it.
The purpose of Packet Criticality is to allow the producer to tell the consumer whether it would prefer a new, unknown packet to generate an error or be ignored .</t> The purpose of Packet Criticality is to allow the producer to tell the consumer whether it would prefer a new, unknown packet to generate an error or be ignored .</t>
<t>Note that previous versions of this document did not have a concept of
<t>Note that previous versions of this document did not have a concept of Packet Packet Criticality and did not give clear guidance on what to do when unknown pa
Criticality, and did not give clear guidance on what to do when unknown packets ckets are encountered. Therefore, implementations of the previous versions may r
are encountered. eject unknown non-critical packets or accept unknown critical packets.</t>
Therefore, implementations of older versions of this document may reject unknown <t>When generating a sequence of OpenPGP packets according to one of the t
non-critical packets, or accept unknown critical packets.</t> hree grammars, an implementation <bcp14>MUST NOT</bcp14> inject a critical packe
t of a type that does not adhere to the grammar.</t>
<t>When generating a sequence of OpenPGP packets according to one of the three g <t>When consuming a sequence of OpenPGP packets, if an implementation enco
rammars, an implementation <bcp14>MUST NOT</bcp14> inject a critical packet of a unters a critical packet of an inappropriate type according to the relevant gram
type that does not adhere to the grammar.</t> mar, the implementation <bcp14>MUST</bcp14> reject the sequence with an error.</
t>
<t>When consuming a sequence of OpenPGP packets according to one of the three gr <section anchor="transferable-public-keys">
ammars, an implementation <bcp14>MUST</bcp14> reject the sequence with an error <name>Transferable Public Keys</name>
if it encounters a critical packet of inappropriate type according to the gramma <t>OpenPGP users may transfer public keys.
r.</t>
<section anchor="transferable-public-keys"><name>Transferable Public Keys</name>
<t>OpenPGP users may transfer public keys.
This section describes the structure of public keys in transit to ensure interop erability. This section describes the structure of public keys in transit to ensure interop erability.
An OpenPGP Transferable Public Key is also known as an OpenPGP certificate, in o An OpenPGP Transferable Public Key is also known as an OpenPGP certificate, in o
rder to distinguish it from both its constituent Public-Key packets (<xref targe rder to distinguish it from both its constituent Public Key packets (Sections <x
t="pubkey"/> and <xref target="pubsubkey"/>) and the underlying cryptographic ke ref target="pubkey" format="counter"/> and <xref target="pubsubkey" format="coun
y material.</t> ter"/>) and the underlying cryptographic key material.</t>
<section anchor="v6-certificate-structures">
<section anchor="v6-certificate-structures"><name>OpenPGP v6 Certificate Structu <name>OpenPGP Version 6 Certificate Structure</name>
re</name> <t>The format of an OpenPGP version 6 certificate is as follows.
<t>The format of an OpenPGP v6 certificate is as follows.
Entries in square brackets are optional and ellipses indicate repetition.</t> Entries in square brackets are optional and ellipses indicate repetition.</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
Primary Key Primary Key
[Revocation Signature...] [Revocation Signature...]
Direct Key Signature... Direct Key Signature...
[User ID or User Attribute [User ID or User Attribute
[Certification Revocation Signature...] [Certification Revocation Signature...]
[Certification Signature...]]... [Certification Signature...]]...
[Subkey [Subkey Revocation Signature...] [Subkey [Subkey Revocation Signature...]
Subkey Binding Signature...]... Subkey Binding Signature...]...
[Padding] [Padding]
]]></artwork></figure> ]]></artwork>
<t>In addition to these rules, a Marker packet (<xref target="marker-p
<t>In addition to these rules, a marker packet (<xref target="marker-packet"/>) acket"/>) can appear anywhere in the sequence.</t>
can appear anywhere in the sequence.</t> <t>Note that a version 6 key uses a self-signed Direct Key signature t
o store algorithm preferences.</t>
<t>Note, that a v6 key uses a self-signed direct key signature to store algorith <t>Every subkey for a version 6 primary key <bcp14>MUST</bcp14> be a v
m preferences.</t> ersion 6 subkey.
Every subkey <bcp14>MUST</bcp14> have at least one Subkey Binding signature.
<t>Every subkey for a v6 primary key <bcp14>MUST</bcp14> be a v6 subkey. Every Subkey Binding signature <bcp14>MUST</bcp14> be a self-signature (that is,
Every subkey <bcp14>MUST</bcp14> have at least one subkey binding signature. made by the version 6 primary key).
Every subkey binding signature <bcp14>MUST</bcp14> be a self-signature (that is, Like all other signatures, every self-signature made by a version 6 key <bcp14>M
made by the v6 primary key). UST</bcp14> be a version 6 signature.</t>
Like all other signatures, every self-signature made by a v6 key <bcp14>MUST</bc </section>
p14> be a v6 signature.</t> <section anchor="v6-revocation-certificate">
<name>OpenPGP Version 6 Revocation Certificate</name>
</section> <t>When a primary version 6 Public Key is revoked, it is sometimes dis
<section anchor="v6-revocation-certificate"><name>OpenPGP v6 Revocation Certific tributed with only the Revocation Signature:</t>
ate</name> <artwork><![CDATA[
<t>When a primary v6 Public Key is revoked, it is sometimes distributed with onl
y the revocation signature:</t>
<figure><artwork><![CDATA[
Primary Key Primary Key
Revocation Signature Revocation Signature
]]></artwork></figure> ]]></artwork>
<t>In this case, the Direct Key signature is no longer necessary, sinc
<t>In this case, the direct key signature is no longer necessary, since the prim e the primary key itself has been marked as unusable.</t>
ary key itself has been marked as unusable.</t> </section>
<section anchor="openpgp-v4-certificate-structure">
</section> <name>OpenPGP Version 4 Certificate Structure</name>
<section anchor="openpgp-v4-certificate-structure"><name>OpenPGP v4 Certificate <t>The format of an OpenPGP version 4 key is as follows.</t>
Structure</name> <artwork><![CDATA[
<t>The format of an OpenPGP v4 key is as follows.</t>
<figure><artwork><![CDATA[
Primary Key Primary Key
[Revocation Signature] [Revocation Signature]
[Direct Key Signature...] [Direct Key Signature...]
[User ID or User Attribute [Signature...]]... [User ID or User Attribute [Signature...]]...
[Subkey [Subkey Revocation Signature...] [Subkey [Subkey Revocation Signature...]
Subkey Binding Signature...]... Subkey Binding Signature...]...
]]></artwork></figure> ]]></artwork>
<t>In addition to these rules, a Marker packet (<xref target="marker-p
<t>In addition to these rules, a marker packet (<xref target="marker-packet"/>) acket"/>) can appear anywhere in the sequence.</t>
can appear anywhere in the sequence.</t> <t>A subkey always has at least one Subkey Binding signature after it
that is issued using the primary key to tie the two keys together. These binding
<t>A subkey always has at least one subkey binding signature after it that is is signatures may be in either version 3 or version 4 format, but they <bcp14>SHOU
sued using the primary key to tie the two keys together. LD</bcp14> be in version 4 format.
These binding signatures may be in either v3 or v4 format, but <bcp14>SHOULD</bc Subkeys that can issue signatures <bcp14>MUST</bcp14> have a version 4 binding s
p14> be in v4 format. ignature due to the <bcp14>REQUIRED</bcp14> embedded Primary Key Binding signatu
Subkeys that can issue signatures <bcp14>MUST</bcp14> have a v4 binding signatur re.</t>
e due to the <bcp14>REQUIRED</bcp14> embedded primary key binding signature.</t> <t>Every subkey for a version 4 primary key <bcp14>MUST</bcp14> be a v
ersion 4 subkey.</t>
<t>Every subkey for a v4 primary key <bcp14>MUST</bcp14> be a v4 subkey.</t> <t>When a primary version 4 Public Key is revoked, the Revocation Sign
ature is sometimes distributed by itself, without the primary key packet it appl
<t>When a primary v4 Public Key is revoked, the revocation signature is sometime ies to. This is referred to as a "revocation certificate".
s distributed by itself, without the primary key packet it applies to. This is r Instead, a version 6 revocation certificate <bcp14>MUST</bcp14> include the prim
eferred to as a "revocation certificate". ary key packet, as described in <xref target="v6-revocation-certificate"/>.</t>
Instead, a v6 revocation certificate <bcp14>MUST</bcp14> include the primary key </section>
packet, as described in <xref target="v6-revocation-certificate"/>.</t> <section anchor="openpgp-v3-key-structure">
<name>OpenPGP Version 3 Key Structure</name>
</section> <t>The format of an OpenPGP version 3 key is as follows.</t>
<section anchor="openpgp-v3-key-structure"><name>OpenPGP v3 Key Structure</name> <artwork><![CDATA[
<t>The format of an OpenPGP v3 key is as follows.</t>
<figure><artwork><![CDATA[
RSA Public Key RSA Public Key
[Revocation Signature] [Revocation Signature]
User ID [Signature...] User ID [Signature...]
[User ID [Signature...]]... [User ID [Signature...]]...
]]></artwork></figure> ]]></artwork>
<t>In addition to these rules, a Marker packet (<xref target="marker-p
<t>In addition to these rules, a marker packet (<xref target="marker-packet"/>) acket"/>) can appear anywhere in the sequence.</t>
can appear anywhere in the sequence.</t> <t>Each signature certifies the RSA public key and the preceding User
ID.
<t>Each signature certifies the RSA public key and the preceding User ID. The RSA public key can have many User IDs, and each User ID can have many signat
The RSA public key can have many User IDs and each User ID can have many signatu ures.
res. Version 3 keys are deprecated. Implementations <bcp14>MUST NOT</bcp14> generate
V3 keys are deprecated. new version 3 keys but <bcp14>MAY</bcp14> continue to use existing ones.</t>
Implementations <bcp14>MUST NOT</bcp14> generate new v3 keys, but <bcp14>MAY</bc <t>Version 3 keys <bcp14>MUST NOT</bcp14> have subkeys.</t>
p14> continue to use existing ones.</t> </section>
<section anchor="common-requirements">
<t>V3 keys <bcp14>MUST NOT</bcp14> have subkeys.</t> <name>Common Requirements</name>
<t>The Public Key packet occurs first.</t>
</section> <t>The primary key <bcp14>MUST</bcp14> be an algorithm capable of maki
<section anchor="common-requirements"><name>Common requirements</name> ng signatures (that is, not an encryption-only algorithm). This is because the p
rimary key needs to be able to create self-signatures (see <xref target="self-si
<t>The Public-Key packet occurs first.</t> gs"/>).
The subkeys may be keys of any type. For example, there may be a single-key RSA
<t>The primary key <bcp14>MUST</bcp14> be an algorithm capable of making signatu key, an Ed25519 primary key with an RSA encryption subkey, an Ed25519 primary ke
res (that is, not an encryption-only algorithm). y with an X25519 subkey, etc.</t>
This is because the primary key needs to be able to create self-signatures (see <t>Each of the following User ID packets provides the identity of the
<xref target="self-sigs"/>). owner of this public key.
The subkeys may be keys of any type. If there are multiple User ID packets, this corresponds to multiple means of ide
For example, there may be a single-key RSA key, an Ed25519 primary key with an R ntifying the same unique individual user; for example, a user may have more than
SA encryption subkey, or an Ed25519 primary key with an X25519 subkey, etc.</t> one email address and construct a User ID for each one.
A Transferable Public Key <bcp14>SHOULD</bcp14> include at least one User ID pac
<t>Each of the following User ID packets provides the identity of the owner of t ket unless storage requirements prohibit this.</t>
his public key. <t>Immediately following each User ID packet, there are zero or more S
If there are multiple User ID packets, this corresponds to multiple means of ide ignature packets.
ntifying the same unique individual user; for example, a user may have more than Each Signature packet is calculated on the immediately preceding User ID packet
one email address, and construct a User ID for each one. and the initial Public Key packet. The signature serves to certify the correspon
A transferable public key <bcp14>SHOULD</bcp14> include at least one User ID pac ding public key and User ID. In effect, the signer is testifying to the belief t
ket unless storage requirements prohibit this.</t> hat this public key belongs to the user identified by this User ID.</t>
<t>Within the same section as the User ID packets, there are zero or m
<t>Immediately following each User ID packet, there are zero or more Signature p ore User Attribute packets. Like the User ID packets, a User Attribute packet is
ackets. followed by zero or more Signature packets calculated on the immediately preced
Each Signature packet is calculated on the immediately preceding User ID packet ing User Attribute packet and the initial Public Key packet.</t>
and the initial Public-Key packet. <t>User Attribute packets and User ID packets may be freely intermixed
The signature serves to certify the corresponding public key and User ID. in this section, as long as the signatures that follow them are maintained on t
In effect, the signer is testifying to his or her belief that this public key be he proper User Attribute or User ID packet.</t>
longs to the user identified by this User ID.</t> <t>After the sequence of User ID packets and Attribute packets and the
ir associated signatures, zero or more Subkey packets follow, each with their ow
<t>Within the same section as the User ID packets, there are zero or more User A n signatures. In general, subkeys are provided in cases where the top-level publ
ttribute packets. ic key is a certification-only key.
Like the User ID packets, a User Attribute packet is followed by zero or more Si However, any version 4 or version 6 key may have subkeys, and the subkeys may be
gnature packets calculated on the immediately preceding User Attribute packet an encryption keys, signing keys, authentication keys, etc.
d the initial Public-Key packet.</t> It is good practice to use separate subkeys for every operation (i.e., signature
-only, encryption-only, authentication-only keys, etc.).</t>
<t>User Attribute packets and User ID packets may be freely intermixed in this s <t>Each Subkey packet <bcp14>MUST</bcp14> be followed by one Signature
ection, so long as the signatures that follow them are maintained on the proper packet, which should be a Subkey Binding signature issued by the top-level key.
User Attribute or User ID packet.</t> For subkeys that can issue signatures, the Subkey Binding signature <bcp14>MUST<
/bcp14> contain an Embedded Signature subpacket with a Primary Key Binding signa
<t>After the sequence of User ID packets and Attribute packets and their associa ture (Type ID 0x19) issued by the subkey on the top-level key.</t>
ted signatures, zero or more Subkey packets follow, each with their own signatur <t>Subkey and Key packets may each be followed by a Revocation Signatu
es. re packet to indicate that the key is revoked.
In general, subkeys are provided in cases where the top-level public key is a ce Revocation Signatures are only accepted if they are issued by the key itself or
rtification-only key. by a key that is authorized to issue revocations via a Revocation Key subpacket
However, any v4 or v6 key may have subkeys, and the subkeys may be encryption ke in a self-signature by the top-level key.</t>
ys, signing keys, authentication keys, etc. <t>The optional trailing Padding packet is a mechanism to defend again
It is good practice to use separate subkeys for every operation (i.e. signature- st traffic analysis (see <xref target="traffic-analysis"/>).
only, encryption-only, authentication-only keys, etc.).</t> For maximum interoperability, if the Public Key packet is a version 4 key, the o
ptional Padding packet <bcp14>SHOULD NOT</bcp14> be present unless the recipient
<t>Each Subkey packet <bcp14>MUST</bcp14> be followed by one Signature packet, w has indicated that they are capable of ignoring it successfully.
hich should be a subkey binding signature issued by the top-level key. An implementation that is capable of receiving a Transferable Public Key with a
For subkeys that can issue signatures, the subkey binding signature <bcp14>MUST< version 6 Public Key primary key <bcp14>MUST</bcp14> be able to accept (and igno
/bcp14> contain an Embedded Signature subpacket with a primary key binding signa re) the trailing optional Padding packet.</t>
ture (0x19) issued by the subkey on the top-level key.</t> <t>Transferable Public Key packet sequences may be concatenated to all
ow transferring multiple public keys in one operation (see <xref target="keyring
<t>Subkey and Key packets may each be followed by a revocation Signature packet s"/>).</t>
to indicate that the key is revoked. </section>
Revocation signatures are only accepted if they are issued by the key itself, or </section>
by a key that is authorized to issue revocations via a Revocation Key subpacket <section anchor="transferable-secret-keys">
in a self-signature by the top-level key.</t> <name>Transferable Secret Keys</name>
<t>OpenPGP users may transfer secret keys.
<t>The optional trailing Padding packet is a mechanism to defend against traffic The format of a Transferable Secret Key is the same as a Transferable Pub
analysis (see <xref target="traffic-analysis"/>). lic Key except that Secret Key and Secret Subkey packets can be used in addition
For maximum interoperability, if the Public-Key packet is a v4 key, the optional to the Public Key and Public Subkey packets. If a single Secret Key or Secret S
Padding packet <bcp14>SHOULD NOT</bcp14> be present unless the recipient has in ubkey packet is included in a packet sequence, it is a Transferable Secret Key a
dicated that they are capable of ignoring it successfully. nd should be handled and marked as such (see <xref target="armor-header-line"/>)
An implementation that is capable of receiving a transferable public key with a .
v6 Public-Key primary key <bcp14>MUST</bcp14> be able to accept (and ignore) the An implementation <bcp14>SHOULD</bcp14> include self-signatures on any User IDs
trailing optional Padding packet.</t> and subkeys, as this allows for a complete public key to be automatically extrac
ted from the Transferable Secret Key. An implementation <bcp14>MAY</bcp14> choos
<t>Transferable public-key packet sequences may be concatenated to allow transfe e to omit the self-signatures, especially if a Transferable Public Key accompani
rring multiple public keys in one operation (see <xref target="keyrings"/>).</t> es the Transferable Secret Key.</t>
</section>
</section> <section anchor="openpgp-messages">
</section> <name>OpenPGP Messages</name>
<section anchor="transferable-secret-keys"><name>Transferable Secret Keys</name> <t>An OpenPGP Message is a packet or sequence of packets that adheres to
the following grammatical rules (a comma (,) represents sequential composition,
<t>OpenPGP users may transfer secret keys. and a vertical bar (|) separates alternatives):</t>
The format of a transferable secret key is the same as a transferable public key <dl>
except that Secret-Key and Secret-Subkey packets can be used in addition to the <dt>OpenPGP Message:</dt>
Public-Key and Public-Subkey packets. <dd>
If a single Secret-Key or Secret-Subkey packet is included in a packet sequence, <t>Encrypted Message | Signed Message | Compressed Message | Literal
it is a transferable secret key and should be handled and marked as such (see < Message.</t>
xref target="forming-ascii-armor"/>). </dd>
An implementation <bcp14>SHOULD</bcp14> include self-signatures on any User IDs <dt>Compressed Message:</dt>
and subkeys, as this allows for a complete public key to be automatically extrac <dd>
ted from the transferable secret key. <t>Compressed Data Packet.</t>
An implementation <bcp14>MAY</bcp14> choose to omit the self-signatures, especia </dd>
lly if a transferable public key accompanies the transferable secret key.</t> <dt>Literal Message:</dt>
<dd>
</section> <t>Literal Data Packet.</t>
<section anchor="openpgp-messages"><name>OpenPGP Messages</name> </dd>
<dt>ESK:</dt>
<t>An OpenPGP message is a packet or sequence of packets that corresponds to the <dd>
following grammatical rules (comma (,) represents sequential composition, and v <t>Public Key Encrypted Session Key Packet | Symmetric Key Encrypted
ertical bar (|) separates alternatives):</t> Session Key Packet.</t>
</dd>
<dl> <dt>ESK Sequence:</dt>
<dt>OpenPGP Message :-</dt> <dd>
<dd> <t>ESK | ESK Sequence, ESK.</t>
<t>Encrypted Message | Signed Message | Compressed Message | Literal Message </dd>
.</t> <dt>Encrypted Data:</dt>
</dd> <dd>
<dt>Compressed Message :-</dt> <t>Symmetrically Encrypted Data Packet | Symmetrically Encrypted and
<dd> Integrity Protected Data Packet.</t>
<t>Compressed Data Packet.</t> </dd>
</dd> <dt>Encrypted Message:</dt>
<dt>Literal Message :-</dt> <dd>
<dd> <t>Encrypted Data | ESK Sequence, Encrypted Data.</t>
<t>Literal Data Packet.</t> </dd>
</dd> <dt>One-Pass Signed Message:</dt>
<dt>ESK :-</dt> <dd>
<dd> <t>One-Pass Signature Packet, OpenPGP Message, Corresponding Signatu
<t>Public-Key Encrypted Session Key Packet | Symmetric-Key Encrypted Session re Packet.</t>
Key Packet.</t> </dd>
</dd> <dt>Signed Message:</dt>
<dt>ESK Sequence :-</dt> <dd>
<dd> <t>Signature Packet, OpenPGP Message | One-Pass Signed Message.</t>
<t>ESK | ESK Sequence, ESK.</t> </dd>
</dd> <dt>Optionally Padded Message:</dt>
<dt>Encrypted Data :-</dt> <dd>
<dd> <t>OpenPGP Message | OpenPGP Message, Padding Packet.</t>
<t>Symmetrically Encrypted Data Packet | Symmetrically Encrypted Integrity P </dd>
rotected Data Packet</t> </dl>
</dd> <t>In addition to these rules, a Marker packet (<xref target="marker-pac
<dt>Encrypted Message :-</dt> ket"/>) can appear anywhere in the sequence.</t>
<dd> <section anchor="unwrapping">
<t>Encrypted Data | ESK Sequence, Encrypted Data.</t> <name>Unwrapping Encrypted and Compressed Messages</name>
</dd> <t>In addition to the above grammar, certain messages can be "unwrappe
<dt>One-Pass Signed Message :-</dt> d" to yield new messages.
<dd>
<t>One-Pass Signature Packet, OpenPGP Message, Corresponding Signature Packe
t.</t>
</dd>
<dt>Signed Message :-</dt>
<dd>
<t>Signature Packet, OpenPGP Message | One-Pass Signed Message.</t>
</dd>
<dt>Optionally Padded Message :-</dt>
<dd>
<t>OpenPGP Message | OpenPGP Message, Padding Packet.</t>
</dd>
</dl>
<t>In addition to these rules, a marker packet (<xref target="marker-packet"/>)
can appear anywhere in the sequence.</t>
<section anchor="unwrapping"><name>Unwrapping Encrypted and Compressed Messages<
/name>
<t>In addition to the above grammar, certain messages can be "unwrapped" to yiel
d new messages.
In particular:</t> In particular:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>Decrypting a version 2 Symmetrically Encrypted and Integrity Protected Data <t>Decrypting a version 2 Symmetrically Encrypted and Integrity Pr
packet <bcp14>MUST</bcp14> yield a valid Optionally Padded Message.</t> otected Data packet <bcp14>MUST</bcp14> yield a valid Optionally Padded Message.
<t>Decrypting a version 1 Symmetrically Encrypted and Integrity Protected Data </t>
packet or --- for historic data --- a Symmetrically Encrypted Data packet <bcp1 </li>
4>MUST</bcp14> yield a valid OpenPGP Message.</t> <li>
<t>Decompressing a Compressed Data packet <bcp14>MUST</bcp14> also yield a val <t>Decrypting a version 1 Symmetrically Encrypted and Integrity Pr
id OpenPGP Message.</t> otected Data packet or -- for historic data -- a Symmetrically Encrypted Data pa
</list></t> cket <bcp14>MUST</bcp14> yield a valid OpenPGP Message.</t>
</li>
<t>When any unwrapping is performed, the resulting stream of octets is parsed in <li>
to a series of OpenPGP packets like any other stream of octets. <t>Decompressing a Compressed Data packet <bcp14>MUST</bcp14> also
yield a valid OpenPGP Message.</t>
</li>
</ul>
<t>When any unwrapping is performed, the resulting stream of octets is
parsed into a series of OpenPGP packets like any other stream of octets.
The packet boundaries found in the series of octets are expected to align with t he length of the unwrapped octet stream. The packet boundaries found in the series of octets are expected to align with t he length of the unwrapped octet stream.
An implementation <bcp14>MUST NOT</bcp14> interpret octets beyond the boundaries of the unwrapped octet stream as part of any OpenPGP packet. An implementation <bcp14>MUST NOT</bcp14> interpret octets beyond the boundaries of the unwrapped octet stream as part of any OpenPGP packet.
If an implementation encounters a packet whose header length indicates that it w ould extend beyond the boundaries of the unwrapped octet stream, the implementat ion <bcp14>MUST</bcp14> reject that packet as malformed and unusable.</t> If an implementation encounters a packet whose header length indicates that it w ould extend beyond the boundaries of the unwrapped octet stream, the implementat ion <bcp14>MUST</bcp14> reject that packet as malformed and unusable.</t>
</section>
</section> <section anchor="additional-constraints-on-packet-sequences">
<section anchor="additional-constraints-on-packet-sequences"><name>Additional Co <name>Additional Constraints on Packet Sequences</name>
nstraints on Packet Sequences</name> <t>Note that some subtle combinations that are formally acceptable by
this grammar are nonetheless unacceptable.</t>
<t>Note that some subtle combinations that are formally acceptable by this gramm <section anchor="encrypted-message-versions">
ar are nonetheless unacceptable.</t> <name>Packet Versions in Encrypted Messages</name>
<t>As noted above, an Encrypted Message is a sequence of zero or mor
<section anchor="encrypted-message-versions"><name>Packet Versions in Encrypted e PKESK packets (<xref target="pkesk"/>) and SKESK packets (<xref target="skesk"
Messages</name> />), followed by an SEIPD (<xref target="seipd"/>) payload. In some historic dat
a, the payload may be a deprecated SED packet (<xref target="sed"/>) instead of
<t>As noted above, an Encrypted Message is a sequence of zero or more PKESKs (<x SEIPD, though implementations <bcp14>MUST NOT</bcp14> generate SED packets (see
ref target="pkesk"/>) and SKESKs (<xref target="skesk"/>), followed by an SEIPD <xref target="ciphertext-malleability"/>).
(<xref target="seipd"/>) payload.
In some historic data, the payload may be a deprecated SED (<xref target="sed"/>
) packet instead of SEIPD, though implementations <bcp14>MUST NOT</bcp14> genera
te SED packets (see <xref target="ciphertext-malleability"/>).
The versions of the preceding ESK packets within an Encrypted Message <bcp14>MUS T</bcp14> align with the version of the payload SEIPD packet, as described in th is section.</t> The versions of the preceding ESK packets within an Encrypted Message <bcp14>MUS T</bcp14> align with the version of the payload SEIPD packet, as described in th is section.</t>
<t>v3 PKESK and v4 SKESK packets both contain the Symmetric Cipher A
<t>v3 PKESK and v4 SKESK packets both contain in their cleartext the symmetric c lgorithm ID and the session key for the subsequent SEIPD packet in their clearte
ipher algorithm ID in addition to the session key for the subsequent SEIPD packe xt.
t.
Since a v1 SEIPD does not contain a symmetric algorithm ID, all ESK packets prec eding a v1 SEIPD payload <bcp14>MUST</bcp14> be either v3 PKESK or v4 SKESK.</t> Since a v1 SEIPD does not contain a symmetric algorithm ID, all ESK packets prec eding a v1 SEIPD payload <bcp14>MUST</bcp14> be either v3 PKESK or v4 SKESK.</t>
<t>On the other hand, the cleartext of the v6 ESK packets (either PK
<t>On the other hand, the cleartext of the v6 ESK packets (either PKESK or SKESK ESK or SKESK) do not contain a Symmetric Cipher Algorithm ID, so they cannot be
) do not contain a symmetric cipher algorithm ID, so they cannot be used in comb used in combination with a v1 SEIPD payload.
ination with a v1 SEIPD payload.
The payload following any v6 PKESK or v6 SKESK packet <bcp14>MUST</bcp14> be a v 2 SEIPD.</t> The payload following any v6 PKESK or v6 SKESK packet <bcp14>MUST</bcp14> be a v 2 SEIPD.</t>
<t>Additionally, to avoid potentially conflicting cipher algorithm I
<t>Additionally, to avoid potentially conflicting cipher algorithm IDs, and for Ds, and for simplicity, implementations <bcp14>MUST NOT</bcp14> precede a v2 SEI
simplicity, implementations <bcp14>MUST NOT</bcp14> precede a v2 SEIPD payload w PD payload with either v3 PKESK or v4 SKESK packets.</t>
ith either v3 PKESK or v4 SKESK packets.</t> <t>The versions of packets found in an Encrypted Message are summari
zed in the following table.
<t>The versions of packets found in an Encrypted Message are summarized in the f
ollowing table.
An implementation <bcp14>MUST</bcp14> only generate an Encrypted Message using p acket versions that match a row with "Yes" in the "Generate?" column. An implementation <bcp14>MUST</bcp14> only generate an Encrypted Message using p acket versions that match a row with "Yes" in the "Generate?" column.
Other rows are provided for the purpose of historic interoperability. Other rows are provided for the purpose of historic interoperability.
A conforming implementation <bcp14>MUST</bcp14> only generate an Encrypted Messa ge using packets whose versions correspond to a single row.</t> A conforming implementation <bcp14>MUST</bcp14> only generate an Encrypted Messa ge using packets whose versions correspond to a single row.</t>
<table anchor="encrypted-packet-versions-registry">
<texttable title="OpenPGP Encrypted Message Packet Versions registry" anchor="en <name>OpenPGP Encrypted Message Packet Versions Registry</name>
crypted-packet-versions-registry"> <thead>
<ttcol align='left'>Version of Encrypted Data payload</ttcol> <tr>
<ttcol align='left'>Version of preceding Symmetric-Key ESK (if any)</ttcol <th align="left">Version of Encrypted Data Payload</th>
> <th align="left">Version of Preceding Symmetric Key ESK (If An
<ttcol align='left'>Version of preceding Public-Key ESK (if any)</ttcol> y)</th>
<ttcol align='left'>Generate?</ttcol> <th align="left">Version of Preceding Public Key ESK (If Any)<
<c>SED (<xref target="sed"/>)</c> /th>
<c>-</c> <th align="left">Generate?</th>
<c>v2 PKESK (<xref target="RFC2440"/>)</c> </tr>
<c>No</c> </thead>
<c>SED (<xref target="sed"/>)</c> <tbody>
<c>v4 SKESK (<xref target="v4-skesk"/>)</c> <tr>
<c>v3 PKESK (<xref target="v3-pkesk"/>)</c> <td align="left">SED (<xref target="sed"/>)</td>
<c>No</c> <td align="left">-</td>
<c>v1 SEIPD (<xref target="version-one-seipd"/>)</c> <td align="left">v2 PKESK <xref target="RFC2440"/></td>
<c>v4 SKESK (<xref target="v4-skesk"/>)</c> <td align="left">No</td>
<c>v3 PKESK (<xref target="v3-pkesk"/>)</c> </tr>
<c>Yes</c> <tr>
<c>v2 SEIPD (<xref target="version-two-seipd"/>)</c> <td align="left">SED (<xref target="sed"/>)</td>
<c>v6 SKESK (<xref target="v6-skesk"/>)</c> <td align="left">v4 SKESK (<xref target="v4-skesk"/>)</td>
<c>v6 PKESK (<xref target="v6-pkesk"/>)</c> <td align="left">v3 PKESK (<xref target="v3-pkesk"/>)</td>
<c>Yes</c> <td align="left">No</td>
</texttable> </tr>
<tr>
<t>An implementation processing an Encrypted Message <bcp14>MUST</bcp14> discard <td align="left">v1 SEIPD (<xref target="version-one-seipd"/>)
any preceding ESK packet with a version that does not align with the version of </td>
the payload.</t> <td align="left">v4 SKESK (<xref target="v4-skesk"/>)</td>
<td align="left">v3 PKESK (<xref target="v3-pkesk"/>)</td>
</section> <td align="left">Yes</td>
<section anchor="signed-message-versions"><name>Packet Versions in Signatures</n </tr>
ame> <tr>
<td align="left">v2 SEIPD (<xref target="version-two-seipd"/>)
<t>OpenPGP key packets and signature packets are also versioned. </td>
<td align="left">v6 SKESK (<xref target="v6-skesk"/>)</td>
<td align="left">v6 PKESK (<xref target="v6-pkesk"/>)</td>
<td align="left">Yes</td>
</tr>
</tbody>
</table>
<t>An implementation processing an Encrypted Message <bcp14>MUST</bc
p14> discard any preceding ESK packet with a version that does not align with th
e version of the payload.</t>
</section>
<section anchor="signed-message-versions">
<name>Packet Versions in Signatures</name>
<t>OpenPGP Key packets and Signature packets are also versioned.
The version of a Signature typically matches the version of the signing key. The version of a Signature typically matches the version of the signing key.
When a v6 key produces a signature packet, it <bcp14>MUST</bcp14> produce a vers ion 6 signature packet, regardless of the signature packet type. When a version 6 key produces a Signature packet, it <bcp14>MUST</bcp14> produce a version 6 Signature packet, regardless of the Signature packet type.
When a message is signed or verified using the one-pass construction, the versio n of the One-Pass Signature packet (<xref target="one-pass-sig"/>) should also b e aligned to the other versions.</t> When a message is signed or verified using the one-pass construction, the versio n of the One-Pass Signature packet (<xref target="one-pass-sig"/>) should also b e aligned to the other versions.</t>
<t>Some legacy implementations have produced unaligned signature ver
<t>Some legacy implementations have produced unaligned signature versions for ol sions for older key material, which are also described in the table below for th
der key material, which are also described in the table below for purpose of his e purpose of historic interoperability.
toric interoperability. A conforming implementation <bcp14>MUST</bcp14> only generate Signature packets
A conforming implementation <bcp14>MUST</bcp14> only generate signature packets with version numbers matching rows with "Yes" in the "Generate?" column.</t>
with version numbers matching rows with "Yes" in the "Generate?" column.</t> <table anchor="signed-packet-versions-registry">
<name>OpenPGP Key and Signature Versions Registry</name>
<texttable title="OpenPGP Key and Signature Versions registry" anchor="signed-pa <thead>
cket-versions-registry"> <tr>
<ttcol align='left'>Signing key version</ttcol> <th align="left">Signing Key Version</th>
<ttcol align='left'>Signature packet version</ttcol> <th align="left">Signature Packet Version</th>
<ttcol align='left'>OPS packet version</ttcol> <th align="left">OPS Packet Version</th>
<ttcol align='left'>Generate?</ttcol> <th align="left">Generate?</th>
<c>3 (<xref target="v3-pubkeys"/>)</c> </tr>
<c>3 (<xref target="version-three-sig"/>)</c> </thead>
<c>3 <xref target="one-pass-sig"/></c> <tbody>
<c>No</c> <tr>
<c>4 (<xref target="v4-pubkeys"/>)</c> <td align="left">3 (<xref target="v3-pubkeys"/>)</td>
<c>3 (<xref target="version-three-sig"/>)</c> <td align="left">3 (<xref target="version-three-sig"/>)</td>
<c>3 <xref target="one-pass-sig"/></c> <td align="left">3 (<xref target="one-pass-sig"/>)</td>
<c>No</c> <td align="left">No</td>
<c>4 (<xref target="v4-pubkeys"/>)</c> </tr>
<c>4 (<xref target="version-four-and-six-sig"/>)</c> <tr>
<c>3 <xref target="one-pass-sig"/></c> <td align="left">4 (<xref target="v4-pubkeys"/>)</td>
<c>Yes</c> <td align="left">3 (<xref target="version-three-sig"/>)</td>
<c>6 (<xref target="v6-pubkeys"/>)</c> <td align="left">3 (<xref target="one-pass-sig"/>)</td>
<c>6 (<xref target="version-four-and-six-sig"/>)</c> <td align="left">No</td>
<c>6 <xref target="one-pass-sig"/></c> </tr>
<c>Yes</c> <tr>
</texttable> <td align="left">4 (<xref target="v4-pubkeys"/>)</td>
<td align="left">4 (<xref target="version-four-and-six-sig"/>)
<t>Note, however, that a version mismatch between these packets does not invalid </td>
ate the packet sequence as a whole, it merely invalidates the signature, as a si <td align="left">3 (<xref target="one-pass-sig"/>)</td>
gnature with an unknown version <bcp14>SHOULD</bcp14> be discarded (see <xref ta <td align="left">Yes</td>
rget="malformed-signatures"/>).</t> </tr>
<tr>
</section> <td align="left">6 (<xref target="v6-pubkeys"/>)</td>
</section> <td align="left">6 (<xref target="version-four-and-six-sig"/>)
</section> </td>
<section anchor="detached-signatures"><name>Detached Signatures</name> <td align="left">6 (<xref target="one-pass-sig"/>)</td>
<td align="left">Yes</td>
<t>Some OpenPGP applications use so-called "detached signatures". </tr>
For example, a program bundle may contain a file, and with it a second file that </tbody>
is a detached signature of the first file. </table>
These detached signatures are simply one or more Signature packets stored separa <t>Note, however, that a version mismatch between these packets does
tely from the data for which they are a signature.</t> not invalidate the packet sequence as a whole; it merely invalidates the signat
ure, as a signature with an unknown version <bcp14>SHOULD</bcp14> be discarded (
<t>In addition, a marker packet (<xref target="marker-packet"/>) and a padding p see <xref target="malformed-signatures"/>).</t>
acket (<xref target="padding-packet"/>) can appear anywhere in the sequence.</t> </section>
</section>
</section> </section>
</section> <section anchor="detached-signatures">
<section anchor="elliptic-curve-cryptography"><name>Elliptic Curve Cryptography< <name>Detached Signatures</name>
/name> <t>Some OpenPGP applications use so-called "detached signatures".
For example, a program bundle may contain a file, and with it a second file that
<t>This section describes algorithms and parameters used with Elliptic Curve Cry is a detached signature of the first file. These detached signatures are simply
ptography (ECC) keys. one or more Signature packets stored separately from the data for which they ar
A thorough introduction to ECC can be found in <xref target="KOBLITZ"/>.</t> e a signature.</t>
<t>In addition, a Marker packet (<xref target="marker-packet"/>) and a P
<t>None of the ECC methods described in this document are allowed with deprecate adding packet (<xref target="padding-packet"/>) can appear anywhere in the seque
d v3 keys. nce.</t>
Refer to <xref target="FIPS186"/>, B.4.1, for the method to generate a uniformly </section>
distributed ECC private key.</t> </section>
<section anchor="elliptic-curve-cryptography">
<section anchor="ecc-curves"><name>ECC Curves</name> <name>Elliptic Curve Cryptography</name>
<t>This section describes algorithms and parameters used with Elliptic Cur
<t>This document references three named prime field curves defined in <xref targ ve Cryptography (ECC) keys. A thorough introduction to ECC can be found in <xref
et="FIPS186"/> as "Curve P-256", "Curve P-384", and "Curve P-521"; and three nam target="KOBLITZ"/>. Refer to <xref target="FIPS186"/>, Appendix B.4, for the me
ed prime field curves defined in <xref target="RFC5639"/> as "brainpoolP256r1", thods to generate a uniformly distributed ECC private key.</t>
"brainpoolP384r1", and "brainpoolP512r1". <t>None of the ECC methods described in this document are allowed with dep
The three <xref target="FIPS186"/> curves and the three <xref target="RFC5639"/> recated version 3 keys. </t>
curves can be used with ECDSA and ECDH public key algorithms. <section anchor="ecc-curves">
They are referenced using a sequence of octets, referred to as the curve OID. <name>ECC Curves</name>
<xref target="ec-curves"/> describes in detail how this sequence of octets is fo <t>This document references three named prime field curves defined in <x
rmed.</t> ref target="FIPS186"/> as "Curve P-256", "Curve P-384", and "Curve P-521" and th
ree named prime field curves defined in <xref target="RFC5639"/> as "brainpoolP2
<t>Separate algorithms are also defined for the use of X25519 and X448, defined 56r1", "brainpoolP384r1", and "brainpoolP512r1". All six curves can be used with
in <xref target="RFC7748"/>; and Ed25519 and Ed448, defined in <xref target="RFC ECDSA and ECDH public key algorithms. They are referenced using a sequence of o
8032"/>. ctets, referred to as the curve OID. <xref target="ec-curves"/> describes in det
ail how this sequence of octets is formed.</t>
<t>Separate algorithms are also defined for the use of X25519 and X448 <
xref target="RFC7748"/> and Ed25519 and Ed448 <xref target="RFC8032"/>.
Additionally, legacy OIDs are defined for "Curve25519Legacy" (for encryption usi ng the ECDH algorithm) and "Ed25519Legacy" (for signing using the EdDSALegacy al gorithm).</t> Additionally, legacy OIDs are defined for "Curve25519Legacy" (for encryption usi ng the ECDH algorithm) and "Ed25519Legacy" (for signing using the EdDSALegacy al gorithm).</t>
</section>
</section> <section anchor="ec-point-wire-formats">
<section anchor="ec-point-wire-formats"><name>EC Point Wire Formats</name> <name>EC Point Wire Formats</name>
<t>A point on an elliptic curve will always be represented on the wire a
<t>A point on an elliptic curve will always be represented on the wire as an MPI s an MPI.
.
Each curve uses a specific point format for the data within the MPI itself. Each curve uses a specific point format for the data within the MPI itself.
Each format uses a designated prefix octet to ensure that the high octet has at Each format uses a designated prefix octet to ensure that the high octet has at
least one bit set to make the MPI a constant size.</t> least 1 bit set to make the MPI a constant size.</t>
<table anchor="ec-point-wire-formats-registry">
<texttable title="OpenPGP Elliptic Curve Point Wire Formats registry" anchor="ec <name>OpenPGP Elliptic Curve Point Wire Formats Registry</name>
-point-wire-formats-registry"> <thead>
<ttcol align='right'>Name</ttcol> <tr>
<ttcol align='left'>Wire Format</ttcol> <th align="right">Name</th>
<ttcol align='left'>Reference</ttcol> <th align="left">Wire Format</th>
<c>SEC1</c> <th align="left">Reference</th>
<c>0x04 || x || y</c> </tr>
<c><xref target="ec-point-sec1"/></c> </thead>
<c>Prefixed native</c> <tbody>
<c>0x40 || native</c> <tr>
<c><xref target="ec-point-prefixed-native"/></c> <td align="right">SEC1</td>
</texttable> <td align="left">0x04 || x || y</td>
<td align="left">
<section anchor="ec-point-sec1"><name>SEC1 EC Point Wire Format</name> <xref target="ec-point-sec1"/></td>
</tr>
<t>For a SEC1-encoded (uncompressed) point the content of the MPI is:</t> <tr>
<td align="right">Prefixed native</td>
<figure><artwork><![CDATA[ <td align="left">0x40 || native</td>
<td align="left">
<xref target="ec-point-prefixed-native"/></td>
</tr>
</tbody>
</table>
<section anchor="ec-point-sec1">
<name>SEC1 EC Point Wire Format</name>
<t>For a SEC1-encoded (uncompressed) point, the content of the MPI is:
</t>
<artwork><![CDATA[
B = 04 || x || y B = 04 || x || y
]]></artwork></figure> ]]></artwork>
<t>where x and y are coordinates of the point P = (x, y), and each is
<t>where x and y are coordinates of the point P = (x, y), and each is encoded in encoded in the big-endian format and zero-padded to the adjusted underlying fiel
the big-endian format and zero-padded to the adjusted underlying field size. d size.
The adjusted underlying field size is the underlying field size rounded up to th e nearest 8-bit boundary, as noted in the "fsize" column in <xref target="ec-cur ves"/>. The adjusted underlying field size is the underlying field size rounded up to th e nearest 8-bit boundary, as noted in the "fsize" column in <xref target="ec-cur ves"/>.
This encoding is compatible with the definition given in <xref target="SEC1"/>.< /t> This encoding is compatible with the definition given in <xref target="SEC1"/>.< /t>
</section>
</section> <section anchor="ec-point-prefixed-native">
<section anchor="ec-point-prefixed-native"><name>Prefixed Native EC Point Wire F <name>Prefixed Native EC Point Wire Format</name>
ormat</name> <t>For a custom compressed point, the content of the MPI is:</t>
<artwork><![CDATA[
<t>For a custom compressed point the content of the MPI is:</t>
<figure><artwork><![CDATA[
B = 40 || p B = 40 || p
]]></artwork></figure> ]]></artwork>
<t>where p is the public key of the point encoded using the rules defi
<t>where p is the public key of the point encoded using the rules defined for th ned for the specified curve.
e specified curve. This format is used for ECDH keys based on curves expressed in Montgomery form a
This format is used for ECDH keys based on curves expressed in Montgomery form, nd for points when using EdDSA.</t>
and for points when using EdDSA.</t> </section>
<section anchor="notes-on-ec-point-wire-formats">
</section> <name>Notes on EC Point Wire Formats</name>
<section anchor="notes-on-ec-point-wire-formats"><name>Notes on EC Point Wire Fo <t>Given the above definitions, the exact size of the MPI payload for
rmats</name> an encoded point is 515 bits for both NIST P-256 and brainpoolP256r1, 771 for bo
th NIST P-384 and brainpoolP384r1, 1059 for NIST P-521, 1027 for brainpoolP512r1
<t>Given the above definitions, the exact size of the MPI payload for an encoded , and 263 for both Curve25519Legacy and Ed25519Legacy. For example, the length o
point is 515 bits for both NIST P-256 and brainpoolP256r1, 771 for both NIST P- f an EdDSALegacy public key for the curve Ed25519Legacy is 263 bits: 7 bits to r
384 and brainpoolP384r1, 1059 for NIST P-521, 1027 for brainpoolP512r1, and 263 epresent the 0x40 prefix octet and 32 octets for the native value of the public
for both Curve25519Legacy and Ed25519Legacy. key.</t>
For example, the length of a EdDSALegacy public key for the curve Ed25519Legacy <t>Even though the zero point (also called the "point at infinity") ma
is 263 bits: 7 bits to represent the 0x40 prefix octet and 32 octets for the nat y occur as a result of arithmetic operations on points of an elliptic curve, it
ive value of the public key.</t> <bcp14>SHALL NOT</bcp14> appear in data structures defined in this document.</t>
<t>Each particular curve uses a designated wire format for the point f
<t>Even though the zero point, also called the point at infinity, may occur as a ound in its public key or ECDH data structure.
result of arithmetic operations on points of an elliptic curve, it <bcp14>SHALL An implementation <bcp14>MUST NOT</bcp14> use a different wire format for a poin
NOT</bcp14> appear in data structures defined in this document.</t> t other than the wire format associated with the curve.</t>
</section>
<t>Each particular curve uses a designated wire format for the point found in it </section>
s public key or ECDH data structure. <section anchor="ec-scalar-wire-formats">
An implementation <bcp14>MUST NOT</bcp14> use a different wire format for a poin <name>EC Scalar Wire Formats</name>
t than the wire format associated with the curve.</t> <t>Some non-curve values in elliptic curve cryptography (for example, se
cret keys and signature components) are not points on a curve, but they are also
</section> encoded on the wire in OpenPGP as an MPI.</t>
</section> <t>Because of different patterns of deployment, some curves treat these
<section anchor="ec-scalar-wire-formats"><name>EC Scalar Wire Formats</name> values as opaque bit strings with the high bit set, while others are treated as
actual integers, encoded in the standard OpenPGP big-endian form.
<t>Some non-curve values in elliptic curve cryptography (for example, secret key The choice of encoding is specific to the public key algorithm in use.</t
s and signature components) are not points on a curve, but are also encoded on t >
he wire in OpenPGP as an MPI.</t> <table anchor="ec-scalar-wire-formats-registry">
<name>OpenPGP Elliptic Curve Scalar Encodings Registry</name>
<t>Because of different patterns of deployment, some curves treat these values a <thead>
s opaque bit strings with the high bit set, while others are treated as actual i <tr>
ntegers, encoded in the standard OpenPGP big-endian form. <th align="left">Type</th>
The choice of encoding is specific to the public key algorithm in use.</t> <th align="left">Description</th>
<th align="left">Reference</th>
<texttable title="OpenPGP Elliptic Curve Scalar Encodings registry" anchor="ec-s </tr>
calar-wire-formats-registry"> </thead>
<ttcol align='left'>Type</ttcol> <tbody>
<ttcol align='left'>Description</ttcol> <tr>
<ttcol align='left'>Reference</ttcol> <td align="left">integer</td>
<c>integer</c> <td align="left">An integer encoded in big-endian format as a stan
<c>An integer, big-endian encoded as a standard OpenPGP MPI</c> dard OpenPGP MPI</td>
<c><xref target="mpi"/></c> <td align="left">
<c>octet string</c> <xref target="mpi"/></td>
<c>An octet string of fixed length, that may be shorter on the wire due to </tr>
leading zeros being stripped by the MPI encoding, and may need to be zero-padde <tr>
d before use</c> <td align="left">octet string</td>
<c><xref target="ec-octet-string"/></c> <td align="left">An octet string of fixed length that may be short
<c>prefixed N octets</c> er on the wire due to leading zeros being stripped by the MPI encoding and may n
<c>An octet string of fixed length N, prefixed with octet 0x40 to ensure n eed to be zero-padded before use</td>
o leading zero octet</c> <td align="left">
<c><xref target="ec-prefix"/></c> <xref target="ec-octet-string"/></td>
</texttable> </tr>
<tr>
<section anchor="ec-octet-string"><name>EC Octet String Wire Format</name> <td align="left">prefixed N octets</td>
<td align="left">An octet string of fixed length N, prefixed with
<t>Some opaque strings of octets are represented on the wire as an MPI by simply octet 0x40 to ensure no leading zero octet</td>
stripping the leading zeros and counting the remaining bits. <td align="left">
<xref target="ec-prefix"/></td>
</tr>
</tbody>
</table>
<section anchor="ec-octet-string">
<name>EC Octet String Wire Format</name>
<t>Some opaque strings of octets are represented on the wire as an MPI
by simply stripping the leading zeros and counting the remaining bits.
These strings are of known, fixed length. These strings are of known, fixed length.
They are represented in this document as <spanx style="verb">MPI(N octets of X)< They are represented in this document as <tt>MPI(N octets of X)</tt>, where <tt>
/spanx> where <spanx style="verb">N</spanx> is the expected length in octets of N</tt> is the expected length in octets of the octet string.</t>
the octet string.</t> <t>For example, a 5-octet opaque string (<tt>MPI(5 octets of X)</tt>)
where <tt>X</tt> has the value <tt>00 02 EE 19 00</tt> would be represented on t
<t>For example, a five-octet opaque string (<spanx style="verb">MPI(5 octets of he wire as an MPI like so: <tt>00 1A 02 EE 19 00</tt>.</t>
X)</spanx>) where <spanx style="verb">X</spanx> has the value <spanx style="verb <t>To encode <tt>X</tt> to the wire format, set the MPI's 2-octet bit
">00 02 EE 19 00</spanx> would be represented on the wire as an MPI like so: <sp counter to the value of the highest set bit (bit 26, or 0x001A), and do not tran
anx style="verb">00 1A 02 EE 19 00</spanx>.</t> sfer the leading all-zero octet to the wire.</t>
<t>To reverse the process, an implementation can take the following st
<t>To encode <spanx style="verb">X</spanx> to the wire format, we set the MPI's eps, if it knows that X has an expected lenth of, for example, 5 octets:</t>
two-octet bit counter to the value of the highest set bit (bit 26, or 0x001A), a <ul spacing="normal">
nd do not transfer the leading all-zero octet to the wire.</t> <li>
<t>Ensure that the MPI's 2-octet bit count is less than or equal t
<t>To reverse the process, an implementation that knows this value has an expect o 40 (5 octets of 8 bits)</t>
ed length of 5 octets can take the following steps:</t> </li>
<li>
<t><list style="symbols"> <t>Allocate 5 octets, setting all to zero initially</t>
<t>Ensure that the MPI's two-octet bitcount is less than or equal to 40 (5 oct </li>
ets of 8 bits)</t> <li>
<t>Allocate 5 octets, setting all to zero initially</t> <t>Copy the MPI data octets (without the two count octets) into th
<t>Copy the MPI data octets (without the two count octets) into the lower octe e lower octets of the allocated space</t>
ts of the allocated space</t> </li>
</list></t> </ul>
</section>
</section> <section anchor="ec-prefix">
<section anchor="ec-prefix"><name>Elliptic Curve Prefixed Octet String Wire Form <name>EC Prefixed Octet String Wire Format</name>
at</name> <t>Another way to ensure that a fixed-length bytes string is encoded s
imply to the wire while remaining in MPI format is to prefix the byte string wit
<t>Another way to ensure that a fixed-length bytestring is encoded simply to the h a dedicated non-zero octet.
wire while remaining in MPI format is to prefix the bytestring with a dedicated
non-zero octet.
This specification uses 0x40 as the prefix octet. This specification uses 0x40 as the prefix octet.
This is represented in this standard as <spanx style="verb">MPI(prefixed N octet This is represented in this specification as <tt>MPI(prefixed N octets of X)</tt
s of X)</spanx>, where <spanx style="verb">N</spanx> is the known bytestring len >, where <tt>N</tt> is the known byte string length.</t>
gth.</t> <t>For example, a 5-octet opaque string using <tt>MPI(prefixed 5 octet
s of X)</tt> where <tt>X</tt> has the value <tt>00 02 EE 19 00</tt> would be wri
<t>For example, a five-octet opaque string using <spanx style="verb">MPI(prefixe tten to the wire form as: <tt>00 2F 40 00 02 EE 19 00</tt>.</t>
d 5 octets of X)</spanx> where <spanx style="verb">X</spanx> has the value <span <t>To encode the string, prefix it with the octet 0x40 (whose 7th bit
x style="verb">00 02 EE 19 00</spanx> would be written to the wire form as: <spa is set), and then set the MPI's 2-octet bit counter to 47 (0x002F -- 7 bits for
nx style="verb">00 2F 40 00 02 EE 19 00</spanx>.</t> the prefix octet and 40 bits for the string).</t>
<t>To decode the string from the wire, an implementation that knows th
<t>To encode the string, we prefix it with the octet 0x40 (whose 7th bit is set) at the variable is formed in this way can:</t>
, then set the MPI's two-octet bit counter to 47 (0x002F, 7 bits for the prefix <ul spacing="normal">
octet and 40 bits for the string).</t> <li>
<t>ensure that the first three octets of the MPI (the 2-bit count
<t>To decode the string from the wire, an implementation that knows that the var octets plus the prefix octet) are <tt>00 2F 40</tt>, and</t>
iable is formed in this way can:</t> </li>
<li>
<t><list style="symbols"> <t>use the remainder of the MPI directly off the wire.</t>
<t>Ensure that the first three octets of the MPI (the two bit-count octets plu </li>
s the prefix octet) are <spanx style="verb">00 2F 40</spanx>, and</t> </ul>
<t>Use the remainder of the MPI directly off the wire.</t> <t>Note that this is a similar approach to that used in the EC point e
</list></t> ncodings found in <xref target="ec-point-prefixed-native"/>.</t>
</section>
<t>Note that this is a similar approach to that used in the EC point encodings f </section>
ound in <xref target="ec-point-prefixed-native"/>.</t> <section anchor="key-derivation-function">
<name>Key Derivation Function</name>
</section> <t>A key derivation function (KDF) is necessary to implement EC encrypti
</section> on.
<section anchor="key-derivation-function"><name>Key Derivation Function</name>
<t>A key derivation function (KDF) is necessary to implement EC encryption.
The Concatenation Key Derivation Function (Approved Alternative 1) <xref target= "SP800-56A"/> with the KDF hash function that is SHA2-256 <xref target="FIPS180" /> or stronger is <bcp14>REQUIRED</bcp14>.</t> The Concatenation Key Derivation Function (Approved Alternative 1) <xref target= "SP800-56A"/> with the KDF hash function that is SHA2-256 <xref target="FIPS180" /> or stronger is <bcp14>REQUIRED</bcp14>.</t>
<t>For convenience, the synopsis of the encoding method is given below w
<t>For convenience, the synopsis of the encoding method is given below with sign ith significant simplifications attributable to the restricted choice of hash fu
ificant simplifications attributable to the restricted choice of hash functions nctions in this document.
in this document.
However, <xref target="SP800-56A"/> is the normative source of the definition.</ t> However, <xref target="SP800-56A"/> is the normative source of the definition.</ t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
// Implements KDF( X, oBits, Param ); // Implements KDF( X, oBits, Param );
// Input: point X = (x,y) // Input: point X = (x,y)
// oBits - the desired size of output // oBits - the desired size of output
// hBits - the size of output of hash function Hash // hBits - the size of output of hash function Hash
// Param - octets representing the parameters // Param - octets representing the parameters
// Assumes that oBits <= hBits // Assumes that oBits <= hBits
// Convert the point X to the octet string: // Convert the point X to the octet string:
// ZB' = 04 || x || y // ZB' = 04 || x || y
// and extract the x portion from ZB' // and extract the x portion from ZB'
ZB = x; ZB = x;
MB = Hash ( 00 || 00 || 00 || 01 || ZB || Param ); MB = Hash ( 00 || 00 || 00 || 01 || ZB || Param );
return oBits leftmost bits of MB. return oBits leftmost bits of MB.
]]></artwork></figure> ]]></artwork>
<t>Note that ZB in the KDF description above is the compact representati
<t>Note that ZB in the KDF description above is the compact representation of X on of X as defined in <xref section="4.2" sectionFormat="of" target="RFC6090"/>.
as defined in <xref section="4.2" sectionFormat="of" target="RFC6090"/>.</t> </t>
</section>
</section> <section anchor="ecdh">
<section anchor="ecdh"><name>EC DH Algorithm (ECDH)</name> <name>ECDH Algorithm</name>
<t>This section describes the One-Pass Diffie-Hellman method, which is a
<t>The method is a combination of an ECC Diffie-Hellman method to establish a sh combination of the ECC Diffie-Hellman method that establishes a
ared secret, a key derivation method to process the shared secret into a derived shared secret and the key derivation method that processes the
key, and a key wrapping method that uses the derived key to protect a session k shared secret into a derived key. Additionally, this section
ey used to encrypt a message.</t> describes a key wrapping method that uses the derived key to protect
a session key used to encrypt a message.</t>
<t>The One-Pass Diffie-Hellman method C(1, 1, ECC CDH) <xref target="SP800-56A"/ <t>The One-Pass Diffie-Hellman method C(1, 1, ECC CDH) <xref target="SP8
> <bcp14>MUST</bcp14> be implemented with the following restrictions: the ECC CD 00-56A"/> <bcp14>MUST</bcp14> be implemented with the following restrictions: th
H primitive employed by this method is modified to always assume the cofactor is e ECC Cofactor Diffie-Hellman (CDH) primitive employed by this method is modifie
1, the KDF specified in <xref target="key-derivation-function"/> is used, and t d to always assume the cofactor is 1, the KDF specified in <xref target="key-der
he KDF parameters specified below are used.</t> ivation-function"/> is used, and the KDF parameters specified below are used.</t
>
<t>The KDF parameters are encoded as a concatenation of the following 5 variable <t>The KDF parameters are encoded as a concatenation of the following 5
-length and fixed-length fields, which are compatible with the definition of the variable-length and fixed-length fields, which are compatible with the definitio
OtherInfo bitstring <xref target="SP800-56A"/>:</t> n of the OtherInfo bit string <xref target="SP800-56A"/>:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>A variable-length field containing a curve OID, which is formatted as follo <t>A variable-length field containing a curve OID, which is formatte
ws: <list style="symbols"> d as follows: </t>
<t>A one-octet size of the following field,</t> <ul spacing="normal">
<t>The octets representing a curve OID defined in <xref target="ec-curves" <li>
/>;</t> <t>A 1-octet size of the following field.</t>
</list></t> </li>
<t>A one-octet public key algorithm ID defined in <xref target="pubkey-algos"/ <li>
>;</t> <t>The octets representing a curve OID, as defined in <xref targ
<t>A variable-length field containing KDF parameters, which are identical to t et="ec-curves"/>.</t>
he corresponding field in the ECDH public key, and are formatted as follows: <l </li>
ist style="symbols"> </ul>
<t>A one-octet size of the following fields; values 0 and 0xFF are reserve </li>
d for future extensions,</t> <li>
<t>A one-octet value 0x01, reserved for future extensions,</t> <t>A 1-octet public key algorithm ID, as defined in <xref target="pu
<t>A one-octet hash function ID used with the KDF,</t> bkey-algos"/>.</t>
<t>A one-octet algorithm ID for the symmetric algorithm used to wrap the s </li>
ymmetric key for message encryption; see <xref target="ecdh"/> for details;</t> <li>
</list></t> <t>A variable-length field containing KDF parameters, which are iden
<t>20 octets representing the UTF-8 encoding of the string <spanx style="verb" tical to the corresponding field in the ECDH public key and formatted as follows
>Anonymous Sender    </spanx>, which is the octet sequence 41 6E 6F 6E 79 6D 6F : </t>
75 73 20 53 65 6E 64 65 72 20 20 20 20;</t> <ul spacing="normal">
<t>A variable-length field containing the fingerprint of the recipient encrypt <li>
ion subkey identifying the key material that is needed for decryption. <t>A 1-octet size of the following fields; values 0 and 0xFF are
reserved for future extensions.</t>
</li>
<li>
<t>A 1-octet value 0x01, reserved for future extensions.</t>
</li>
<li>
<t>A 1-octet hash function ID used with the KDF.</t>
</li>
<li>
<t>A 1-octet algorithm ID for the symmetric algorithm that is us
ed to wrap the symmetric key for message encryption; see <xref target="ecdh"/> f
or details.</t>
</li>
</ul>
</li>
<li>
<t>20 octets representing the UTF-8 encoding of the string "Anonymou
s Sender" padded at the end with spaces (0x20) to 20 octets, which is the octet
sequence 41 6E 6F 6E 79 6D 6F 75 73 20 53 65 6E 64 65 72 20 20 20 20.</t>
</li>
<li>
<t>A variable-length field containing the fingerprint of the recipie
nt encryption subkey identifying the key material that is needed for decryption.
For version 4 keys, this field is 20 octets. For version 4 keys, this field is 20 octets.
For version 6 keys, this field is 32 octets.</t> For version 6 keys, this field is 32 octets.</t>
</list></t> </li>
</ul>
<t>The size in octets of the KDF parameters sequence, defined above, for encrypt <t>The size in octets of the KDF parameters sequence, as defined above,
ing to a v4 key is either 54 for curve NIST P-256, 51 for curves NIST P-384 and for encrypting to a version 4 key is 54 for curve NIST P-256; 51 for curves NIST
NIST P-521, 55 for curves brainpoolP256r1, brainpoolP384r1 and brainpoolP512r1, P-384 and NIST P-521; 55 for curves brainpoolP256r1, brainpoolP384r1, and brain
or 56 for Curve25519Legacy. poolP512r1; or 56 for Curve25519Legacy. For encrypting to a version 6 key, the s
For encrypting to a v6 key, the size of the sequence is either 66 for curve NIST ize of the sequence is 66 for curve NIST P-256; 63 for curves NIST P-384 and NIS
P-256, 63 for curves NIST P-384 and NIST P-521, or 67 for curves brainpoolP256r T P-521; or 67 for curves brainpoolP256r1, brainpoolP384r1, and brainpoolP512r1.
1, brainpoolP384r1 and brainpoolP512r1.</t> </t>
<t>The key wrapping method is described in <xref target="RFC3394"/>.
<t>The key wrapping method is described in <xref target="RFC3394"/>. The KDF produces a symmetric key that is used as a KEK as specified in <xref tar
The KDF produces a symmetric key that is used as a key-encryption key (KEK) as s get="RFC3394"/>. Refer to <xref target="ecdh-parameters"/> for the details regar
pecified in <xref target="RFC3394"/>. ding the choice of the KEK algorithm, which <bcp14>SHOULD</bcp14> be one of the
Refer to <xref target="ecdh-parameters"/> for the details regarding the choice o three AES algorithms.
f the KEK algorithm, which <bcp14>SHOULD</bcp14> be one of the three AES algorit
hms.
Key wrapping and unwrapping is performed with the default initial value of <xref target="RFC3394"/>.</t> Key wrapping and unwrapping is performed with the default initial value of <xref target="RFC3394"/>.</t>
<t>To produce the input to the key wrapping method, first concatenate th
<t>To produce the input to the key wrapping method, first concatenate the follow e following values:</t>
ing values:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>The 1-octet algorithm identifier, if it was passed (in the case o
<t>The one-octet algorithm identifier, if it was passed (in the case of a v3 P f a v3 PKESK packet).</t>
KESK packet).</t> </li>
<t>The session key.</t> <li>
<t>A two-octet checksum of the session key, equal to the sum of the session ke <t>The session key.</t>
y octets, modulo 65536.</t> </li>
</list></t> <li>
<t>A 2-octet checksum of the session key, equal to the sum of the se
<t>Then, the above values are padded using the method described in <xref target= ssion key octets, modulo 65536.</t>
"RFC2898"/> to an 8-octet granularity.</t> </li>
</ul>
<t>For example, in a v3 Public-Key Encrypted Session Key packet, an AES-256 sess <t>Then, the above values are padded to an 8-octet granularity using the
ion key is encoded as follows, forming a 40 octet sequence:</t> method described in <xref target="RFC8018"/>.</t>
<t>For example, in a version 3 Public Key Encrypted Session Key packet,
<figure><artwork><![CDATA[ an AES-256 session key is encoded as follows, forming a 40-octet sequence:</t>
<artwork><![CDATA[
09 k0 k1 ... k31 s0 s1 05 05 05 05 05 09 k0 k1 ... k31 s0 s1 05 05 05 05 05
]]></artwork></figure> ]]></artwork>
<t>The octets k0 to k31 above denote the session key, and the octets s0
<t>The octets k0 to k31 above denote the session key, and the octets s0 and s1 d and s1 denote the checksum of the session key octets.
enote the checksum of the session key octets.
This encoding allows the sender to obfuscate the size of the symmetric encryptio n key used to encrypt the data. This encoding allows the sender to obfuscate the size of the symmetric encryptio n key used to encrypt the data.
For example, assuming that an AES algorithm is used for the session key, the sen der <bcp14>MAY</bcp14> use 21, 13, and 5 octets of padding for AES-128, AES-192, and AES-256, respectively, to provide the same number of octets, 40 total, as a n input to the key wrapping method.</t> For example, assuming that an AES algorithm is used for the session key, the sen der <bcp14>MAY</bcp14> use 21, 13, and 5 octets of padding for AES-128, AES-192, and AES-256, respectively, to provide the same number of octets, 40 total, as a n input to the key wrapping method.</t>
<t>In a version 6 Public Key Encrypted Session Key packet, the symmetric
<t>In a v6 Public-Key Encrypted Session Key packet, the symmetric algorithm is n algorithm is not included, as described in <xref target="pkesk"/>.
ot included, as described in <xref target="pkesk"/>.
For example, an AES-256 session key would be composed as follows:</t> For example, an AES-256 session key would be composed as follows:</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
k0 k1 ... k31 s0 s1 06 06 06 06 06 06 k0 k1 ... k31 s0 s1 06 06 06 06 06 06
]]></artwork></figure> ]]></artwork>
<t>The octets k0 to k31 above again denote the session key, and the octe
<t>The octets k0 to k31 above again denote the session key, and the octets s0 an ts s0 and s1 denote the checksum.
d s1 denote the checksum.
In this case, assuming that an AES algorithm is used for the session key, the se nder <bcp14>MAY</bcp14> use 22, 14, and 6 octets of padding for AES-128, AES-192 , and AES-256, respectively, to provide the same number of octets, 40 total, as an input to the key wrapping method.</t> In this case, assuming that an AES algorithm is used for the session key, the se nder <bcp14>MAY</bcp14> use 22, 14, and 6 octets of padding for AES-128, AES-192 , and AES-256, respectively, to provide the same number of octets, 40 total, as an input to the key wrapping method.</t>
<t>The output of the method consists of two fields.
<t>The output of the method consists of two fields.
The first field is the MPI containing the ephemeral key used to establish the sh ared secret. The first field is the MPI containing the ephemeral key used to establish the sh ared secret.
The second field is composed of the following two subfields:</t> The second field is composed of the following two subfields:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>One octet encoding the size in octets of the result of the key wrapping met <t>One octet encoding the size in octets of the result of the key wr
hod; the value 255 is reserved for future extensions;</t> apping method; the value 255 is reserved for future extensions.</t>
<t>Up to 254 octets representing the result of the key wrapping method, applie </li>
d to the 8-octet padded session key, as described above.</t> <li>
</list></t> <t>Up to 254 octets representing the result of the key wrapping meth
od, applied to the 8-octet padded session key, as described above.</t>
<t>Note that for session key sizes 128, 192, and 256 bits, the size of the resul </li>
t of the key wrapping method is, respectively, 32, 40, and 48 octets, unless siz </ul>
e obfuscation is used.</t> <t>Note that for session key sizes 128, 192, and 256 bits, the size of t
he result of the key wrapping method is, respectively, 32, 40, and 48 octets, un
<t>For convenience, the synopsis of the encoding method is given below; however, less size obfuscation is used.</t>
this section, <xref target="SP800-56A"/>, and <xref target="RFC3394"/> are the <t>For convenience, the synopsis of the encoding method is given below;
normative sources of the definition.</t> however, this section, <xref target="SP800-56A"/>, and <xref target="RFC3394"/>
are the normative sources of the definition.</t>
<t><list style="symbols"> <ul spacing="normal">
<t>Obtain the authenticated recipient public key R</t> <li>
<t>Generate an ephemeral, single-use key pair {v, V=vG}</t> <t>Obtain the authenticated recipient public key R</t>
<t>Compute the shared point S = vR;</t> </li>
<t>m = symm_alg_ID || session key || checksum || pkcs5_padding;</t> <li>
<t>curve_OID_len = (octet)len(curve_OID);</t> <t>Generate an ephemeral, single-use key pair {v, V=vG}</t>
<t>Param = curve_OID_len || curve_OID || public_key_alg_ID || 03 || 01 || KDF_ </li>
hash_ID || KEK_alg_ID for AESKeyWrap || <spanx style="verb">Anonymous Sender     <li>
</spanx> || recipient_fingerprint;</t> <t>Compute the shared point S = vR</t>
<t>Z_len = the key size for the KEK_alg_ID used with AESKeyWrap</t> </li>
<t>Compute Z = KDF( S, Z_len, Param );</t> <li>
<t>Compute C = AESKeyWrap( Z, m ); (as per <xref target="RFC3394"/>)</t> <t>m = symm_alg_ID || session key || checksum || pkcs5_padding</t>
<t>Wipe the memory that contained S, v, and Z to avoid leaking ephemeral secre </li>
ts</t> <li>
<t>VB = convert point V to the octet string</t> <t>curve_OID_len = (octet)len(curve_OID)</t>
<t>Output (MPI(VB) || len(C) || C).</t> </li>
</list></t> <li>
<t>Param = curve_OID_len || curve_OID || public_key_alg_ID || 03 ||
<t>The decryption is the inverse of the method given. 01 || KDF_hash_ID || KEK_alg_ID for AESKeyWrap || 41 6E 6F 6E 79 6D 6F 75 73 20
53 65 6E 64 65 72 20 20 20 20 || recipient_fingerprint</t>
</li>
<li>
<t>Z_len = the key size for the KEK_alg_ID used with AESKeyWrap</t>
</li>
<li>
<t>Compute Z = KDF( S, Z_len, Param )</t>
</li>
<li>
<t>Compute C = AESKeyWrap( Z, m ) (per <xref target="RFC3394"/>)</t>
</li>
<li>
<t>Wipe the memory that contained S, v, and Z to avoid leaking ephem
eral secrets</t>
</li>
<li>
<t>VB = convert point V to the octet string</t>
</li>
<li>
<t>Output (MPI(VB) || len(C) || C)</t>
</li>
</ul>
<t>The decryption is the inverse of the method given.
Note that the recipient with key pair (r,R) obtains the shared secret by calcula ting:</t> Note that the recipient with key pair (r,R) obtains the shared secret by calcula ting:</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
S = rV = rvG S = rV = rvG
]]></artwork></figure> ]]></artwork>
<section anchor="ecdh-parameters">
<section anchor="ecdh-parameters"><name>ECDH Parameters</name> <name>ECDH Parameters</name>
<t>ECDH keys have a hash algorithm parameter for key derivation and a
<t>ECDH keys have a hash algorithm parameter for key derivation and a symmetric symmetric algorithm for key encapsulation.</t>
algorithm for key encapsulation.</t> <t>For version 6 keys, the following algorithms <bcp14>MUST</bcp14> be
used depending on the curve.
<t>For v6 keys, the following algorithms <bcp14>MUST</bcp14> be used depending o An implementation <bcp14>MUST NOT</bcp14> generate a version 6 ECDH key over any
n the curve. listed curve that uses different KDF or KEK parameters.
An implementation <bcp14>MUST NOT</bcp14> generate a v6 ECDH key over any listed An implementation <bcp14>MUST NOT</bcp14> encrypt any message to a version 6 ECD
curve that uses different KDF or KEK parameters. H key over a listed curve that announces a different KDF or KEK parameter.</t>
An implementation <bcp14>MUST NOT</bcp14> encrypt any message to a v6 ECDH key o <t>For version 4 keys, the following algorithms <bcp14>SHOULD</bcp14>
ver a listed curve that announces a different KDF or KEK parameter.</t> be used depending on the curve.
<t>For v4 keys, the following algorithms <bcp14>SHOULD</bcp14> be used depending
on the curve.
An implementation <bcp14>SHOULD</bcp14> only use an AES algorithm as a KEK algor ithm.</t> An implementation <bcp14>SHOULD</bcp14> only use an AES algorithm as a KEK algor ithm.</t>
<table anchor="ecdh-kdf-kek-parameters-registry">
<name>OpenPGP ECDH KDF and KEK Parameters Registry</name>
<thead>
<tr>
<th align="left">Curve</th>
<th align="left">Hash Algorithm</th>
<th align="left">Symmetric Algorithm</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">NIST P-256</td>
<td align="left">SHA2-256</td>
<td align="left">AES-128</td>
</tr>
<tr>
<td align="left">NIST P-384</td>
<td align="left">SHA2-384</td>
<td align="left">AES-192</td>
</tr>
<tr>
<td align="left">NIST P-521</td>
<td align="left">SHA2-512</td>
<td align="left">AES-256</td>
</tr>
<tr>
<td align="left">brainpoolP256r1</td>
<td align="left">SHA2-256</td>
<td align="left">AES-128</td>
</tr>
<tr>
<td align="left">brainpoolP384r1</td>
<td align="left">SHA2-384</td>
<td align="left">AES-192</td>
</tr>
<tr>
<td align="left">brainpoolP512r1</td>
<td align="left">SHA2-512</td>
<td align="left">AES-256</td>
</tr>
<tr>
<td align="left">Curve25519Legacy</td>
<td align="left">SHA2-256</td>
<td align="left">AES-128</td>
</tr>
</tbody>
</table>
</section>
</section>
</section>
<section anchor="notes-on-algorithms">
<name>Notes on Algorithms</name>
<section anchor="pkcs-encoding">
<name>PKCS#1 Encoding in OpenPGP</name>
<t>This specification makes use of the PKCS#1 functions EME-PKCS1-v1_5 a
nd EMSA-PKCS1-v1_5. However, the calling conventions of these functions have cha
nged in the past. To avoid potential confusion and interoperability problems, we
are including local copies in this document, adapted from those in PKCS#1 v2.1
<xref target="RFC8017"/>. <xref target="RFC8017"/> should be treated as the ulti
mate authority on PKCS#1 for OpenPGP. Nonetheless, we believe that there is valu
e in having a self-contained document that avoids problems in the future with ne
eded changes in the conventions.</t>
<section anchor="eme-pkcs1-v1-5-encode">
<texttable title="OpenPGP ECDH KDF and KEK Parameters registry" anchor="ecdh-kdf <name>EME-PKCS1-v1_5-ENCODE</name>
-kek-parameters-registry"> <t>Input:</t>
<ttcol align='left'>Curve</ttcol> <dl>
<ttcol align='left'>Hash algorithm</ttcol> <dt>k =</dt>
<ttcol align='left'>Symmetric algorithm</ttcol> <dd>key modulus length in octets.
<c>NIST P-256</c> </dd>
<c>SHA2-256</c> <dt>M =</dt>
<c>AES-128</c> <dd>message to be encoded; an octet string of length mLen, where mLe
<c>NIST P-384</c> n &lt;= k - 11.
<c>SHA2-384</c> </dd>
<c>AES-192</c> </dl>
<c>NIST P-521</c> <t>Output:</t>
<c>SHA2-512</c> <dl>
<c>AES-256</c> <dt>EM =</dt>
<c>brainpoolP256r1</c> <dd>encoded message; an octet string of length k.
<c>SHA2-256</c> </dd>
<c>AES-128</c> </dl>
<c>brainpoolP384r1</c> <t>Error: "message too long".</t>
<c>SHA2-384</c> <ol spacing="normal" type="1"><li>
<c>AES-192</c> <t>Length checking: If mLen &gt; k - 11, output "message too long"
<c>brainpoolP512r1</c> and stop.</t>
<c>SHA2-512</c> </li>
<c>AES-256</c> <li>
<c>Curve25519Legacy</c> <t>Generate an octet string PS of length k - mLen - 3 consisting o
<c>SHA2-256</c> f pseudorandomly generated non-zero octets. The length of PS will be at least 8
<c>AES-128</c> octets.</t>
</texttable> </li>
<li>
</section> <t>Concatenate PS, the message M, and other padding to form an enc
</section> oded message EM of length k octets as </t>
</section> <artwork><![CDATA[
<section anchor="notes-on-algorithms"><name>Notes on Algorithms</name>
<section anchor="pkcs-encoding"><name>PKCS#1 Encoding in OpenPGP</name>
<t>This standard makes use of the PKCS#1 functions EME-PKCS1-v1_5 and EMSA-PKCS1
-v1_5.
However, the calling conventions of these functions has changed in the past.
To avoid potential confusion and interoperability problems, we are including loc
al copies in this document, adapted from those in PKCS#1 v2.1 <xref target="RFC8
017"/>.
<xref target="RFC8017"/> should be treated as the ultimate authority on PKCS#1 f
or OpenPGP.
Nonetheless, we believe that there is value in having a self-contained document
that avoids problems in the future with needed changes in the conventions.</t>
<section anchor="eme-pkcs1-v1-5-encode"><name>EME-PKCS1-v1_5-ENCODE</name>
<t>Input:</t>
<dl>
<dt>k =</dt>
<dd>
<t>the length in octets of the key modulus.</t>
</dd>
<dt>M =</dt>
<dd>
<t>message to be encoded, an octet string of length mLen, where mLen &lt;= k
- 11.</t>
</dd>
</dl>
<t>Output:</t>
<dl>
<dt>EM =</dt>
<dd>
<t>encoded message, an octet string of length k.</t>
</dd>
</dl>
<t>Error: "message too long".</t>
<t><list style="numbers">
<t>Length checking: If mLen &gt; k - 11, output "message too long" and stop.</
t>
<t>Generate an octet string PS of length k - mLen - 3 consisting of pseudo-ran
domly generated nonzero octets.
The length of PS will be at least eight octets.</t>
<t>Concatenate PS, the message M, and other padding to form an encoded message
EM of length k octets as <vspace blankLines='1'/>
<figure><artwork><![CDATA[
EM = 0x00 || 0x02 || PS || 0x00 || M. EM = 0x00 || 0x02 || PS || 0x00 || M.
]]></artwork></figure> ]]></artwork>
</t> </li>
<t>Output EM.</t> <li>
</list></t> <t>Output EM.</t>
</li>
</section> </ol>
<section anchor="eme-pkcs1-v1-5-decode"><name>EME-PKCS1-v1_5-DECODE</name> </section>
<section anchor="eme-pkcs1-v1-5-decode">
<t>Input:</t> <name>EME-PKCS1-v1_5-DECODE</name>
<t>Input:</t>
<dl> <dl>
<dt>EM =</dt> <dt>EM =</dt>
<dd> <dd>
<t>encoded message, an octet string</t> <t>encoded message; an octet string.</t>
</dd> </dd>
</dl> </dl>
<t>Output:</t>
<t>Output:</t> <dl>
<dt>M =</dt>
<dl> <dd>
<dt>M =</dt> <t>decoded message; an octet string.</t>
<dd> </dd>
<t>message, an octet string.</t> </dl>
</dd> <t>Error: "decryption error".</t>
</dl> <t>To decode an EME-PKCS1_v1_5 message, separate the encoded message E
M into an octet string PS consisting of non-zero octets and a message M as follo
<t>Error: "decryption error".</t> ws</t>
<artwork><![CDATA[
<t>To decode an EME-PKCS1_v1_5 message, separate the encoded message EM into an
octet string PS consisting of nonzero octets and a message M as follows</t>
<figure><artwork><![CDATA[
EM = 0x00 || 0x02 || PS || 0x00 || M. EM = 0x00 || 0x02 || PS || 0x00 || M.
]]></artwork></figure> ]]></artwork>
<t>If the first octet of EM does not have hexadecimal value 0x00, the
<t>If the first octet of EM does not have hexadecimal value 0x00, if the second second octet of EM does not have hexadecimal value 0x02, there is no octet with
octet of EM does not have hexadecimal value 0x02, if there is no octet with hexa hexadecimal value 0x00 to separate PS from M, or the length of PS is less than 8
decimal value 0x00 to separate PS from M, or if the length of PS is less than 8 octets, output "decryption error" and stop. See also <xref target="pkcs1-errors
octets, output "decryption error" and stop. "/> regarding differences in reporting between a decryption error and a padding
See also <xref target="pkcs1-errors"/> regarding differences in reporting betwee error.</t>
n a decryption error and a padding error.</t> </section>
<section anchor="emsa-pkcs1-v1-5">
</section> <name>EMSA-PKCS1-v1_5</name>
<section anchor="emsa-pkcs1-v1-5"><name>EMSA-PKCS1-v1_5</name> <t>This encoding method is deterministic and only has an encoding oper
ation.</t>
<t>This encoding method is deterministic and only has an encoding operation.</t> <t>Input:</t>
<dl>
<t>Option:</t> <dt>Hash =</dt>
<dd>
<dl> <t>hash function to be used.</t>
<dt>Hash -</dt> </dd>
<dd> <dt>M =</dt>
<t>a hash function in which hLen denotes the length in octets of the hash fu <dd>
nction output.</t> <t>message to be encoded.</t>
</dd> </dd>
</dl> <dt>emLen =</dt>
<dd>
<t>Input:</t> <t>intended length of the encoded message in octets, at least tLen
+ 11, where tLen is the octet length of the DER encoding T of a certain value c
<dl> omputed during the encoding operation.</t>
<dt>M =</dt> </dd>
<dd> </dl>
<t>message to be encoded.</t> <t>Output:</t>
</dd> <dl>
<dt>emLen =</dt> <dt>EM =</dt>
<dd> <dd>
<t>intended length in octets of the encoded message, at least tLen + 11, whe <t>encoded message; an octet string of length emLen.</t>
re tLen is the octet length of the DER encoding T of a certain value computed du </dd>
ring the encoding operation.</t> </dl>
</dd> <t>Errors: "message too long"; "intended encoded message length too sh
</dl> ort".</t>
<t>Steps:</t>
<t>Output:</t> <ol spacing="normal" type="1"><li>
<t>Apply the hash function to the message M to produce hash value
<dl> H: </t>
<dt>EM =</dt> <t>
<dd> H = Hash(M). </t>
<t>encoded message, an octet string of length emLen.</t> <t>
</dd>
</dl>
<t>Errors: "message too long"; "intended encoded message length too short".</t>
<t>Steps:</t>
<t><list style="numbers">
<t>Apply the hash function to the message M to produce a hash value H: <vspac
e blankLines='1'/>
H = Hash(M). <vspace blankLines='1'/>
If the hash function outputs "message too long," output "message too long" and s top.</t> If the hash function outputs "message too long," output "message too long" and s top.</t>
<t>Using the list in <xref target="hash-algos"/>, produce an ASN.1 DER value f </li>
or the hash function used. <li>
Let T be the full hash prefix from the list, and let tLen be the length in octet <t>Let T be the Full Hash Prefix from <xref target="emsa-hash-oids
s of T.</t> -registry"/> for the given hash function, concatenated with the hash digest H (r
<t>If emLen &lt; tLen + 11, output "intended encoded message length too short" epresenting an ASN.1 DER value for the hash function used and the hash digest).
and stop.</t> Let tLen be the length in octets of T.</t>
<t>Generate an octet string PS consisting of emLen - tLen - 3 octets with hexa </li>
decimal value 0xFF. <li>
<t>If emLen &lt; tLen + 11, output "intended encoded message lengt
h too short" and stop.</t>
</li>
<li>
<t>Generate an octet string PS consisting of emLen - tLen - 3 octe
ts with hexadecimal value 0xFF.
The length of PS will be at least 8 octets.</t> The length of PS will be at least 8 octets.</t>
<t>Concatenate PS, the hash prefix T, and other padding to form the encoded me </li>
ssage EM as <vspace blankLines='1'/> <li>
<figure><artwork><![CDATA[ <t>Concatenate PS, the hash prefix T, and other padding to form th
e encoded message EM as </t>
<artwork><![CDATA[
EM = 0x00 || 0x01 || PS || 0x00 || T. EM = 0x00 || 0x01 || PS || 0x00 || T.
]]></artwork></figure> ]]></artwork>
</t> </li>
<t>Output EM.</t> <li>
</list></t> <t>Output EM.</t>
</li>
</section> </ol>
</section> </section>
<section anchor="symmetric-algorithm-preferences"><name>Symmetric Algorithm Pref </section>
erences</name> <section anchor="symmetric-algorithm-preferences">
<name>Symmetric Algorithm Preferences</name>
<t>The symmetric algorithm preference is an ordered list of algorithms that the <t>The symmetric algorithm preference is an ordered list of algorithms t
keyholder accepts. hat the keyholder accepts.
Since it is found on a self-signature, it is possible that a keyholder may have Since it is found on a self-signature, it is possible that a keyholder may have
multiple, different preferences. multiple, different preferences. For example, Alice may have AES-128 only specif
For example, Alice may have AES-128 only specified for "alice@work.com" but Came ied for "alice@work.com" but Camellia-256, Twofish, and AES-128 specified for "a
llia-256, Twofish, and AES-128 specified for "alice@home.org". lice@home.org". Note that it is also possible for preferences to be in a subkey'
Note that it is also possible for preferences to be in a subkey's binding signat s binding signature.</t>
ure.</t> <t>Since AES-128 is the algorithm that <bcp14>MUST</bcp14> be implemente
d, if it is not explicitly in the list, it is tacitly at the end. However, it is
<t>Since AES-128 is the <bcp14>MUST</bcp14>-implement algorithm, if it is not ex good form to place it there explicitly.
plicitly in the list, it is tacitly at the end. Note also that if an implementation does not implement the preference, then it i
However, it is good form to place it there explicitly. s implicitly an AES-128-only implementation. Furthermore, note that implementati
Note also that if an implementation does not implement the preference, then it i ons conforming to the previous version of this specification <xref target="RFC48
s implicitly an AES-128-only implementation. 80"/> have TripleDES as the only algorithm that <bcp14>MUST</bcp14> be implement
Note further that implementations conforming to previous versions of this standa ed.</t>
rd <xref target="RFC4880"/> have TripleDES as its only <bcp14>MUST</bcp14>-imple <t>An implementation <bcp14>MUST NOT</bcp14> use a symmetric algorithm t
ment algorithm.</t> hat is not in the recipient's preference list. When encrypting to more than one
recipient, the implementation finds a suitable algorithm by taking the intersect
<t>An implementation <bcp14>MUST NOT</bcp14> use a symmetric algorithm that is n ion of the preferences of the recipients. Note that since the AES-128 algorithm
ot in the recipient's preference list. <bcp14>MUST</bcp14> be implemented, the intersection is guaranteed to be non-emp
When encrypting to more than one recipient, the implementation finds a suitable ty.</t>
algorithm by taking the intersection of the preferences of the recipients. <t>If an implementation can decrypt a message that a keyholder doesn't h
Note that the <bcp14>MUST</bcp14>-implement algorithm, AES-128, ensures that the ave in their preferences, the implementation <bcp14>SHOULD</bcp14> decrypt the m
intersection is non-empty. essage anyway, but it <bcp14>MUST</bcp14> warn the keyholder. For example, suppo
The implementation may use any mechanism to pick an algorithm in the intersectio se that Alice (above) has an implementation that implements all algorithms in th
n.</t> is specification. Nonetheless, she prefers subsets for work or home. If she is s
ent a message encrypted with IDEA, which is not in her preferences, the implemen
<t>If an implementation can decrypt a message that a keyholder doesn't have in t tation warns her that someone sent an IDEA-encrypted message, but it would ideal
heir preferences, the implementation <bcp14>SHOULD</bcp14> decrypt the message a ly decrypt it anyway.</t>
nyway, but <bcp14>MUST</bcp14> warn the keyholder that the protocol has been vio <section anchor="plaintext">
lated. <name>Plaintext</name>
For example, suppose that Alice, above, has an implementation that implements al <t>Algorithm 0, "plaintext", may only be used to denote secret keys th
l algorithms in this specification. at are stored in the clear.
Nonetheless, she prefers subsets for work or home. An implementation <bcp14>MUST NOT</bcp14> use algorithm 0 as the indicated symme
If she is sent a message encrypted with IDEA, which is not in her preferences, t tric cipher for an encrypted data packet (Sections <xref target="sed" format="co
he implementation warns her that someone sent her an IDEA-encrypted message, but unter"/> or <xref target="seipd" format="counter"/>); it can use a Literal Data
it would ideally decrypt it anyway.</t> packet (<xref target="lit"/>) to encode unencrypted literal data.</t>
</section>
<section anchor="plaintext"><name>Plaintext</name> </section>
<section anchor="other-algorithm-preferences">
<t>Algorithm 0, "plaintext", may only be used to denote secret keys that are sto <name>Other Algorithm Preferences</name>
red in the clear. <t>Other algorithm preferences work similarly to the symmetric algorithm
An implementation <bcp14>MUST NOT</bcp14> use algorithm 0 as the indicated symme preference in that they specify which algorithms the keyholder accepts. There a
tric cipher for an encrypted data packet (<xref target="sed"/> or <xref target=" re two interesting cases in which further comments are needed: the compression p
seipd"/>); it can use a Literal Data packet (<xref target="lit"/>) to encode une references and the hash preferences.</t>
ncrypted literal data.</t> <section anchor="compression-preferences">
<name>Compression Preferences</name>
</section> <t>Like the algorithm preferences, an implementation <bcp14>MUST NOT</
</section> bcp14> use an algorithm that is not in the preference vector.
<section anchor="other-algorithm-preferences"><name>Other Algorithm Preferences<
/name>
<t>Other algorithm preferences work similarly to the symmetric algorithm prefere
nce, in that they specify which algorithms the keyholder accepts.
There are two interesting cases that other comments need to be made about, thoug
h, the compression preferences and the hash preferences.</t>
<section anchor="compression-preferences"><name>Compression Preferences</name>
<t>Like the algorithm preferences, an implementation <bcp14>MUST NOT</bcp14> use
an algorithm that is not in the preference vector.
If Uncompressed (0) is not explicitly in the list, it is tacitly at the end. If Uncompressed (0) is not explicitly in the list, it is tacitly at the end.
That is, uncompressed messages may always be sent.</t> That is, uncompressed messages may always be sent.</t>
<t>Note that earlier implementations may assume that the absence of co
<t>Note that earlier implementations may assume that the absence of compression mpression preferences means that [ZIP(1), Uncompressed(0)] are preferred, and de
preferences means that [ZIP(1), Uncompressed(0)] are preferred, and default to Z fault to ZIP compression.
IP compression. Therefore, an implementation that prefers uncompressed data <bcp14>SHOULD</bcp14
Therefore, an implementation that prefers uncompressed data <bcp14>SHOULD</bcp14 > explicitly state this in the Preferred Compression Algorithms.</t>
> explicitly state this in the preferred compression algorithms.</t> <section anchor="uncompressed">
<name>Uncompressed</name>
<section anchor="uncompressed"><name>Uncompressed</name> <t>Algorithm 0, "uncompressed", may only be used to denote a prefere
nce for uncompressed data.
<t>Algorithm 0, "uncompressed", may only be used to denote a preference for unco
mpressed data.
An implementation <bcp14>MUST NOT</bcp14> use algorithm 0 as the indicated compr ession algorithm in a Compressed Data packet (<xref target="compressed-data"/>); it can use a Literal Data packet (<xref target="lit"/>) to encode uncompressed literal data.</t> An implementation <bcp14>MUST NOT</bcp14> use algorithm 0 as the indicated compr ession algorithm in a Compressed Data packet (<xref target="compressed-data"/>); it can use a Literal Data packet (<xref target="lit"/>) to encode uncompressed literal data.</t>
</section>
</section> </section>
</section> <section anchor="hash-algorithm-preferences">
<section anchor="hash-algorithm-preferences"><name>Hash Algorithm Preferences</n <name>Hash Algorithm Preferences</name>
ame> <t>Typically, the signer chooses which hash algorithm to use, rather t
han the verifier, because a signer rarely knows who is going to be verifying the
<t>Typically, the choice of a hash algorithm is something the signer does, rathe signature. This preference allows a protocol based upon digital signatures ease
r than the verifier, because a signer rarely knows who is going to be verifying in negotiation.</t>
the signature. <t>Thus, if Alice is authenticating herself to Bob with a signature, i
This preference, though, allows a protocol based upon digital signatures ease in t makes sense for her to use a hash algorithm that Bob's implementation uses. Th
negotiation.</t> is preference allows Bob to state which algorithms Alice may use in his key.</t>
<t>Since SHA2-256 is the hash algorithm that <bcp14>MUST</bcp14> be im
<t>Thus, if Alice is authenticating herself to Bob with a signature, it makes se plemented, if it is not explicitly in the list, it is tacitly at the end.
nse for her to use a hash algorithm that Bob's implementation uses.
This preference allows Bob to state in his key which algorithms Alice may use.</
t>
<t>Since SHA2-256 is the <bcp14>MUST</bcp14>-implement hash algorithm, if it is
not explicitly in the list, it is tacitly at the end.
However, it is good form to place it there explicitly.</t> However, it is good form to place it there explicitly.</t>
</section>
</section> </section>
</section> <section anchor="rsa-notes">
<section anchor="rsa-notes"><name>RSA</name> <name>RSA</name>
<t>The PKCS1-v1_5 padding scheme, used by the RSA algorithms defined in
<t>The PKCS1-v1_5 padding scheme, used by the RSA algorithms defined in this doc this document, is no longer recommended, and its use is deprecated by <xref targ
ument, is no longer recommended, and its use is deprecated by <xref target="SP80 et="SP800-131A"/>.
0-131A"/>.
Therefore, an implementation <bcp14>SHOULD NOT</bcp14> generate RSA keys.</t> Therefore, an implementation <bcp14>SHOULD NOT</bcp14> generate RSA keys.</t>
<t>There are algorithm types for RSA Sign-Only and RSA Encrypt-Only keys
<t>There are algorithm types for RSA Sign-Only, and RSA Encrypt-Only keys. . These types are deprecated in favor of the Key Flags signature subpacket. An i
These types are deprecated. mplementation <bcp14>MUST NOT</bcp14> create such a key, but it <bcp14>MAY</bcp1
The "key flags" subpacket in a signature is a much better way to express the sam 4> interpret it.</t>
e idea, and generalizes it to all algorithms. <t>An implementation <bcp14>MUST NOT</bcp14> generate RSA keys of a size
An implementation <bcp14>MUST NOT</bcp14> create such a key, but <bcp14>MAY</bcp less than 3072 bits.
14> interpret it.</t> An implementation <bcp14>SHOULD NOT</bcp14> encrypt, sign, or verify using RSA k
eys of a size less than 3072 bits. An implementation <bcp14>MUST NOT</bcp14> enc
<t>An implementation <bcp14>MUST NOT</bcp14> generate RSA keys of size less than rypt, sign, or verify using RSA keys of a size less than 2048 bits. An implement
3072 bits. ation that decrypts a message using an RSA secret key of a size less than 3072 b
An implementation <bcp14>SHOULD NOT</bcp14> encrypt, sign or verify using RSA ke its <bcp14>SHOULD</bcp14> generate a deprecation warning that the key is too wea
ys of size less than 3072 bits. k for modern use.</t>
An implementation <bcp14>MUST NOT</bcp14> encrypt, sign or verify using RSA keys </section>
of size less than 2048 bits. <section anchor="dsa-notes">
An implementation that decrypts a message using an RSA secret key of size less t <name>DSA</name>
han 3072 bits <bcp14>SHOULD</bcp14> generate a deprecation warning that the key <t>DSA is no longer recommended.
is too weak for modern use.</t>
</section>
<section anchor="dsa-notes"><name>DSA</name>
<t>DSA is no longer recommended.
It has also been deprecated in <xref target="FIPS186"/>. It has also been deprecated in <xref target="FIPS186"/>.
Therefore, an implementation <bcp14>MUST NOT</bcp14> generate DSA keys.</t> Therefore, an implementation <bcp14>MUST NOT</bcp14> generate DSA keys.</t>
<t>An implementation <bcp14>MUST NOT</bcp14> sign or verify using DSA ke
<t>An implementation <bcp14>MUST NOT</bcp14> sign or verify using DSA keys.</t> ys.</t>
</section>
</section> <section anchor="elgamal-notes">
<section anchor="elgamal-notes"><name>Elgamal</name> <name>Elgamal</name>
<t>The PKCS1-v1_5 padding scheme, used by the Elgamal algorithm defined
<t>The PKCS1-v1_5 padding scheme, used by the Elgamal algorithm defined in this in this document, is no longer recommended, and its use is deprecated by <xref t
document, is no longer recommended, and its use is deprecated by <xref target="S arget="SP800-131A"/>.
P800-131A"/>.
Therefore, an implementation <bcp14>MUST NOT</bcp14> generate Elgamal keys.</t> Therefore, an implementation <bcp14>MUST NOT</bcp14> generate Elgamal keys.</t>
<t>An implementation <bcp14>MUST NOT</bcp14> encrypt using Elgamal keys.
<t>An implementation <bcp14>MUST NOT</bcp14> encrypt using Elgamal keys.
An implementation that decrypts a message using an Elgamal secret key <bcp14>SHO ULD</bcp14> generate a deprecation warning that the key is too weak for modern u se.</t> An implementation that decrypts a message using an Elgamal secret key <bcp14>SHO ULD</bcp14> generate a deprecation warning that the key is too weak for modern u se.</t>
</section>
</section> <section anchor="eddsa-notes">
<section anchor="eddsa-notes"><name>EdDSA</name> <name>EdDSA</name>
<t>Although the EdDSA algorithm allows arbitrary data as input, its use
<t>Although the EdDSA algorithm allows arbitrary data as input, its use with Ope with OpenPGP requires that a digest of the message be used as input (pre-hashed)
nPGP requires that a digest of the message is used as input (pre-hashed). . See <xref target="computing-signatures"/> for details.
See <xref target="computing-signatures"/> for details.
Truncation of the resulting digest is never applied; the resulting digest value is used verbatim as input to the EdDSA algorithm.</t> Truncation of the resulting digest is never applied; the resulting digest value is used verbatim as input to the EdDSA algorithm.</t>
<t>For clarity: while <xref target="RFC8032"/> describes different varia
<t>For clarity: while <xref target="RFC8032"/> describes different variants of E nts of EdDSA, OpenPGP uses the "pure" variant (PureEdDSA).
dDSA, OpenPGP uses the "pure" variant (PureEdDSA).
The hashing that happens with OpenPGP is done as part of the standard OpenPGP si gnature process, and that hash itself is fed as the input message to the PureEdD SA algorithm.</t> The hashing that happens with OpenPGP is done as part of the standard OpenPGP si gnature process, and that hash itself is fed as the input message to the PureEdD SA algorithm.</t>
<t>As specified in <xref target="RFC8032"/>, Ed448 also expects a "conte
<t>As specified in <xref target="RFC8032"/>, Ed448 also expects a "context strin xt string".
g".
In OpenPGP, Ed448 is used with the empty string as a context string.</t> In OpenPGP, Ed448 is used with the empty string as a context string.</t>
</section>
<section anchor="reserved-notes">
<name>Reserved Algorithm IDs</name>
<t>A number of algorithm IDs have been reserved for algorithms that woul
d be useful to use in an OpenPGP implementation, yet there are issues that preve
nt an implementer from actually implementing the algorithm. These are marked as
reserved in <xref target="pubkey-algos"/>.</t>
</section> <t>The reserved public key algorithm X9.42 (21) does not have the necess
<section anchor="reserved-notes"><name>Reserved Algorithm IDs</name> ary parameters, parameter order, or semantics defined. The same is currently tru
e for reserved public key algorithms AEDH (23) and AEDSA (24).</t>
<t>A number of algorithm IDs have been reserved for algorithms that would be use <t>Previous versions of the OpenPGP specification permitted Elgamal <xre
ful to use in an OpenPGP implementation, yet there are issues that prevent an im f target="ELGAMAL"/> signatures with a public key algorithm ID of 20. These are
plementer from actually implementing the algorithm. no longer permitted. An implementation <bcp14>MUST NOT</bcp14> generate such key
These are marked as reserved in <xref target="pubkey-algos"/>.</t> s. An implementation <bcp14>MUST NOT</bcp14> generate Elgamal signatures;
see <xref target="BLEICHENBACHER"/>.</t>
<t>The reserved public-key algorithm X9.42 (21) does not have the necessary para </section>
meters, parameter order, or semantics defined. <section anchor="cfb-mode">
The same is currently true for reserved public-key algorithms AEDH (23) and AEDS <name>CFB Mode</name>
A (24).</t> <t>The Cipher Feedback (CFB) mode used in this document is defined in Se
ction 6.3 of <xref target="SP800-38A"/>.</t>
<t>Previous versions of OpenPGP permitted Elgamal <xref target="ELGAMAL"/> signa <t>The CFB segment size <tt>s</tt> is equal to the block size of the cip
tures with a public-key algorithm ID of 20. her (i.e., n-bit CFB mode, where n is the block size used).</t>
These are no longer permitted. </section>
An implementation <bcp14>MUST NOT</bcp14> generate such keys. <section anchor="private-or-experimental-parameters">
An implementation <bcp14>MUST NOT</bcp14> generate Elgamal signatures. <name>Private or Experimental Parameters</name>
See <xref target="BLEICHENBACHER"/>.</t> <t>S2K Specifiers, Signature Subpacket Type IDs, User Attribute Subpacke
t Type IDs, image format IDs, and the various algorithm IDs described in <xref t
</section> arget="constants"/> all reserve the range 100 to 110 for Private and Experimenta
<section anchor="cfb-mode"><name>CFB Mode</name> l Use.
Packet Type IDs reserve the range 60 to 63 for Private and Experimental Use.
<t>The Cipher Feedback (CFB) mode used in this document is defined in Section 6. These are intentionally managed by the Private Use and Experimental Use policies
3 of <xref target="SP800-38A"/>.</t> , as described in <xref target="RFC8126"/>.</t>
<t>However, implementations need to be careful with these and promote th
<t>The CFB segment size <spanx style="verb">s</spanx> is equal to the block size em to full IANA-managed parameters when they grow beyond the original, limited s
of the cipher (i.e., n-bit CFB mode where n is the block size is used).</t> ystem.</t>
</section>
</section> <section anchor="meta-considerations-for-expansion">
<section anchor="private-or-experimental-parameters"><name>Private or Experiment <name>Meta Considerations for Expansion</name>
al Parameters</name> <t>If OpenPGP is extended in a way that is not backward compatible, mean
ing that old implementations will not gracefully handle their absence of a new f
<t>S2K specifiers, Signature subpacket type IDs, User Attribute subpacket type I eature, the extension proposal can be declared in the keyholder's self-signature
Ds, image format IDs, and the various algorithm IDs described in <xref target="c as part of the Features signature subpacket.</t>
onstants"/> all reserve the range 100 to 110 for private and experimental use. <t>We cannot state definitively what extensions will not be forward comp
Packet type IDs reserve the range 60 to 63 for private and experimental use. atible, but typically new algorithms are forward compatible, whereas new packets
These are intentionally managed with the PRIVATE USE method, as described in <xr are not.</t>
ef target="RFC8126"/>.</t> <t>If an extension proposal does not update the Features system, it <bcp
14>SHOULD</bcp14> include an explanation of why this is unnecessary.
<t>However, implementations need to be careful with these and promote them to fu
ll IANA-managed parameters when they grow beyond the original, limited system.</
t>
</section>
<section anchor="meta-considerations-for-expansion"><name>Meta-Considerations fo
r Expansion</name>
<t>If OpenPGP is extended in a way that is not backwards-compatible, meaning tha
t old implementations will not gracefully handle their absence of a new feature,
the extension proposal can be declared in the keyholder's self-signature as par
t of the Features signature subpacket.</t>
<t>We cannot state definitively what extensions will not be upwards-compatible,
but typically new algorithms are upwards-compatible, whereas new packets are not
.</t>
<t>If an extension proposal does not update the Features system, it <bcp14>SHOUL
D</bcp14> include an explanation of why this is unnecessary.
If the proposal contains neither an extension to the Features system nor an expl anation of why such an extension is unnecessary, the proposal <bcp14>SHOULD</bcp 14> be rejected.</t> If the proposal contains neither an extension to the Features system nor an expl anation of why such an extension is unnecessary, the proposal <bcp14>SHOULD</bcp 14> be rejected.</t>
</section>
</section> </section>
</section> <section anchor="security-considerations">
<section anchor="security-considerations"><name>Security Considerations</name> <name>Security Considerations</name>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>As with any technology involving cryptography, implementers should check th <t>As with any technology involving cryptography, implementers should
e current literature to determine if any algorithms used here have been found to check the current literature to determine if any algorithms used here have been
be vulnerable to an attack. found to be vulnerable to an attack.
If so, implementers should consider disallowing such algorithms for new data and If so, implementers should consider disallowing such algorithms for new data and
warn or prevent the enduser when they are trying to consume data protected by s warning the end user, or preventing use, when they are trying to consume data p
uch now vulnerable algorithms.</t> rotected by such algorithms that are now vulnerable.</t>
<t>This specification uses Public-Key Cryptography technologies. </li>
<li>
<t>This specification uses Public Key Cryptography technologies.
It is assumed that the private key portion of a public-private key pair is contr olled and secured by the proper party or parties.</t> It is assumed that the private key portion of a public-private key pair is contr olled and secured by the proper party or parties.</t>
<t>The MD5 and SHA-1 hash algorithms have been found to have weaknesses, with </li>
collisions found in a number of cases. <li>
MD5 and SHA-1 are deprecated for use in OpenPGP (See <xref target="hash-algos"/> <t>The MD5 and SHA-1 hash algorithms have been found to have weaknesse
).</t> s, with collisions found in a number of cases.
<t>Many security protocol designers think that it is a bad idea to use a singl MD5 and SHA-1 are deprecated for use in OpenPGP (see <xref target="hash-algos"/>
e key for both privacy (encryption) and integrity (signatures). ).</t>
In fact, this was one of the motivating forces behind the v4 key format with sep </li>
arate signature and encryption keys. <li>
Using a single key for encrypting and signing is discouraged.</t> <t>Many security protocol designers think that it is a bad idea to use
<t>The DSA algorithm will work with any hash, but is sensitive to the quality a single key for both privacy (encryption) and integrity (signatures).
of the hash algorithm. In fact, this was one of the motivating forces behind the version 4 key format w
Verifiers should be aware that even if the signer used a strong hash, an attacke ith separate signature and encryption keys. Using a single key for encrypting an
r could have modified the signature to use a weak one. d signing is discouraged.</t>
Only signatures using acceptably strong hash algorithms should be accepted as va </li>
lid.</t> <li>
<t>As OpenPGP combines many different asymmetric, symmetric, and hash algorith <t>The DSA algorithm will work with any hash, but it is sensitive to t
ms, each with different measures of strength, care should be taken that the weak he quality of the hash algorithm.
est element of an OpenPGP message is still sufficiently strong for the purpose a Verifiers should be aware that even if the signer used a strong hash, an attacke
t hand. r could have modified the signature to use a weak one. Only signatures using acc
While consensus about the strength of a given algorithm may evolve, NIST Special eptably strong hash algorithms should be accepted as valid.</t>
Publication 800-57 <xref target="SP800-57"/> contains recommendations current a </li>
t the time of this publication about equivalent security levels of different alg <li>
orithms.</t> <t>As OpenPGP combines many different asymmetric, symmetric, and hash
<t>There is a somewhat-related potential security problem in signatures. algorithms, each with different measures of strength, care should be taken to en
If an attacker can find a message that hashes to the same hash with a different sure that the weakest element of an OpenPGP Message is still sufficiently strong
algorithm, a bogus signature structure can be constructed that evaluates correct for the purpose at hand. While consensus about the strength of a given algorith
ly. <vspace blankLines='1'/> m may evolve, NIST Special Publication 800-57 <xref target="SP800-57"/> contains
For example, suppose Alice DSA signs message M using hash algorithm H. recommendations (current at the time of this publication) about equivalent secu
rity levels of different algorithms.</t>
</li>
<li>
<t>There is a somewhat-related potential security problem in signature
s.
If an attacker can find a message that hashes to the same hash with a different
algorithm, a bogus signature structure can be constructed that evaluates correct
ly. </t>
<t>
For example, suppose Alice DSA-signs message M using hash algorithm H.
Suppose that Mallet finds a message M' that has the same hash value as M with H' . Suppose that Mallet finds a message M' that has the same hash value as M with H' .
Mallet can then construct a signature block that verifies as Alice's signature o f M' with H'. Mallet can then construct a signature block that verifies as Alice's signature o f M' with H'.
However, this would also constitute a weakness in either H or H' or both. However, this would also constitute a weakness in either H or H', or both.
Should this ever occur, a revision will have to be made to this document to revi se the allowed hash algorithms.</t> Should this ever occur, a revision will have to be made to this document to revi se the allowed hash algorithms.</t>
<t>If you are building an authentication system, the recipient may specify a p </li>
referred signing algorithm. <li>
<t>If you are building an authentication system, the recipient may spe
cify a preferred signing algorithm.
However, the signer would be foolish to use a weak algorithm simply because the recipient requests it.</t> However, the signer would be foolish to use a weak algorithm simply because the recipient requests it.</t>
<t>Some of the encryption algorithms mentioned in this document have been anal </li>
yzed less than others. <li>
<t>Some of the encryption algorithms mentioned in this document have b
een analyzed less than others.
For example, although TWOFISH is presently considered reasonably strong, it has been analyzed much less than AES. For example, although TWOFISH is presently considered reasonably strong, it has been analyzed much less than AES.
Other algorithms may have other concerns surrounding them.</t> Other algorithms may have other concerns surrounding them.</t>
<t>In late summer 2002, Jallad, Katz, and Schneier published an interesting at </li>
tack on older versions of the OpenPGP protocol and some of its implementations < <li>
xref target="JKS02"/>. <t>In late summer 2002, Jallad, Katz, and Schneier published an intere
sting attack on previous versions of the OpenPGP specification and some of its i
mplementations <xref target="JKS02"/>.
In this attack, the attacker modifies a message and sends it to a user who then returns the erroneously decrypted message to the attacker. In this attack, the attacker modifies a message and sends it to a user who then returns the erroneously decrypted message to the attacker.
The attacker is thus using the user as a decryption oracle, and can often decryp t the message. The attacker is thus using the user as a decryption oracle and can often decrypt the message.
This attack is a particular form of ciphertext malleability. This attack is a particular form of ciphertext malleability.
See <xref target="ciphertext-malleability"/> for information on how to defend ag ainst such an attack using more recent versions of OpenPGP.</t> See <xref target="ciphertext-malleability"/> for information on how to defend ag ainst such an attack using more recent versions of OpenPGP.</t>
</list></t> </li>
</ul>
<section anchor="sha1cd"><name>SHA-1 Collision Detection</name> <section anchor="sha1cd">
<name>SHA-1 Collision Detection</name>
<t>As described in <xref target="SHAMBLES"/>, the SHA-1 digest algorithm is not <t>As described in <xref target="SHAMBLES"/>, the SHA-1 digest algorithm
collision-resistant. is not collision resistant.
However, an OpenPGP implementation cannot completely discard the SHA-1 algorithm However, an OpenPGP implementation cannot completely discard the SHA-1 algorithm
, because it is required for implementing v4 public keys. , because it is required for implementing version 4 public keys.
In particular, the v4 fingerprint derivation uses SHA-1. In particular, the version 4 fingerprint derivation uses SHA-1.
So as long as an OpenPGP implementation supports v4 public keys, it will need to So as long as an OpenPGP implementation supports version 4 public keys, it will
implement SHA-1 in at least some scenarios.</t> need to implement SHA-1 in at least some scenarios.</t>
<t>To avoid the risk of uncertain breakage from a maliciously introduced
<t>To avoid the risk of uncertain breakage from a maliciously introduced SHA-1 c SHA-1 collision, an OpenPGP implementation <bcp14>MAY</bcp14> attempt to detect
ollision, an OpenPGP implementation <bcp14>MAY</bcp14> attempt to detect when a when a hash input is likely from a known collision attack and then either rejec
hash input is likely from a known collision attack, and then either deliberately t the hash input deliberately or modify the hash output.
reject the hash input or modify the hash output.
This should convert an uncertain breakage (where it is unclear what the effect o f a collision will be) to an explicit breakage, which is more desirable for a ro bust implementation.</t> This should convert an uncertain breakage (where it is unclear what the effect o f a collision will be) to an explicit breakage, which is more desirable for a ro bust implementation.</t>
<t><xref target="STEVENS2013"/> describes a method for detecting indicat
<t><xref target="STEVENS2013"/> describes a method for detecting indicators of w ors of well-known SHA-1 collision attacks.
ell-known SHA-1 collision attacks.
Some example C code implementing this technique can be found at <xref target="SH A1CD"/>.</t> Some example C code implementing this technique can be found at <xref target="SH A1CD"/>.</t>
</section>
</section> <section anchor="signature-salt-rationale">
<section anchor="signature-salt-rationale"><name>Advantages of Salted Signatures <name>Advantages of Salted Signatures</name>
</name> <t>Version 6 signatures include a salt that is hashed first, and it's si
ze depends on the hashing algorithm. This makes version 6 OpenPGP signatures non
<t>V6 signatures include a salt that is hashed first, which size depends on the -deterministic and protects against a broad class of attacks that depend on crea
hashing algorithm. ting a signature over a predictable message. By selecting a new random salt for
This makes v6 OpenPGP signatures non-deterministic and protects against a broad each signature made, the signed hashes and the signatures are not predictable.</
class of attacks that depend on creating a signature over a predictable message. t>
By selecting a new random salt for each signature made, the signed hashes and th <t>While the material to be signed could be attacker controlled, hashing
e signatures are not predictable.</t> the salt first means that there is no attacker-controlled hashed prefix.
An example of this kind of attack is described in the paper "SHA-1 is a Shambles
<t>While the material to be signed could be attacker-controlled, hashing the sal " <xref target="SHAMBLES"/>, which leverages a chosen prefix collision attack ag
t first means that there is no attacker controlled hashed prefix. ainst SHA-1.
An example of this kind of attack is described in the paper "SHA-1 Is A Shambles This means that an adversary carrying out a chosen-message attack will not be ab
" <xref target="SHAMBLES"/>, which leverages a chosen prefix collision attack ag le to control the hash that is being signed and will need to break second-preima
ainst SHA-1. ge resistance instead of the simpler collision resistance to create two messages
This means that an adversary carrying out a chosen-message attack will not be ab having the same signature.
le to control the hash that is being signed, and will need to break second-preim The size of the salt is bound to the hash function to match the expected collisi
age resistance instead of the simpler collision resistance to create two message on-resistance level and is at least 16 octets.</t>
s having the same signature. <t>In some cases, an attacker may be able to induce a signature to be ma
The size of the salt is bound to the hash function to match the expected collisi de, even if they do not control the content of the message. In some scenarios, a
on resistance level, and at least 16 octets.</t> repeated signature over the exact same message may risk leakage of part or all
of the signing key; for example, see discussion of hardware faults over EdDSA an
<t>In some cases, an attacker may be able to induce a signature to be made, even d deterministic ECDSA in <xref target="PSSLR17"/>.
if they do not control the content of the message. Choosing a new random salt for each signature ensures that no repeated signature
In some scenarios, a repeated signature over the exact same message may risk lea s are produced, which mitigates this risk.</t>
kage of part or all of the signing key, for example see discussion of hardware f </section>
aults over EdDSA and deterministic ECDSA in <xref target="PSSLR17"/>. <section anchor="ecc-side-channels">
Choosing a new random salt for each signature ensures that no repeated signature <name>Elliptic Curve Side Channels</name>
s are produced, and mitigates this risk.</t> <t>Side-channel attacks are a concern when a compliant application's use
of the OpenPGP format can be modeled by a decryption or signing oracle, for exa
</section> mple, when an application is a network service performing decryption to unauthen
<section anchor="ecc-side-channels"><name>Elliptic Curve Side Channels</name> ticated remote users.
ECC scalar multiplication operations used in ECDSA and ECDH are vulnerable to si
<t>Side channel attacks are a concern when a compliant application's use of the de-channel attacks. Countermeasures can often be taken at the higher protocol le
OpenPGP format can be modeled by a decryption or signing oracle, for example, wh vel, such as limiting the number of allowed failures or time-blinding the operat
en an application is a network service performing decryption to unauthenticated ions associated with each network interface. Mitigations at the scalar multiplic
remote users. ation level seek to eliminate any measurable distinction between the ECC point a
ECC scalar multiplication operations used in ECDSA and ECDH are vulnerable to si ddition and doubling operations.</t>
de channel attacks. </section>
Countermeasures can often be taken at the higher protocol level, such as limitin <section anchor="quick-check-oracle">
g the number of allowed failures or time-blinding of the operations associated w <name>Risks of a Quick Check Oracle</name>
ith each network interface. <t>In winter 2005, Serge Mister and Robert Zuccherato from Entrust relea
Mitigations at the scalar multiplication level seek to eliminate any measurable sed a paper describing a way that the "quick check" in v1 SEIPD and SED packets
distinction between the ECC point addition and doubling operations.</t> can be used as an oracle to decrypt two octets of every cipher block <xref targe
t="MZ05"/>.
</section>
<section anchor="quick-check-oracle"><name>Risks of a Quick Check Oracle</name>
<t>In winter 2005, Serge Mister and Robert Zuccherato from Entrust released a pa
per describing a way that the "quick check" in v1 SEIPD and SED packets can be u
sed as an oracle to decrypt two octets of every cipher block <xref target="MZ05"
/>.
This check was intended for early detection of session key decryption errors, pa rticularly to detect a wrong passphrase, since v4 SKESK packets do not include a n integrity check.</t> This check was intended for early detection of session key decryption errors, pa rticularly to detect a wrong passphrase, since v4 SKESK packets do not include a n integrity check.</t>
<t>There is a danger when using the quick check if timing or error infor
<t>There is a danger to using the quick check if timing or error information abo mation about the check can be exposed to an attacker, particularly via an automa
ut the check can be exposed to an attacker, particularly via an automated servic ted service that allows rapidly repeated queries.</t>
e that allows rapidly repeated queries.</t> <t>Disabling the quick check prevents the attack.</t>
<t>For very large encrypted data whose session key is protected by a pas
<t>Disabling the quick check prevents the attack.</t> sphrase using a v4 SKESK, the quick check may be convenient to the user by infor
ming them early that they typed the wrong passphrase.
<t>For very large encrypted data whose session key is protected by a passphrase
using a version 4 SKESK, the quick check may be convenient to the user, by infor
ming them early that they typed the wrong passphrase.
But the implementation should use the quick check with care. But the implementation should use the quick check with care.
The recommended approach for secure and early detection of decryption failure is to encrypt data using v2 SEIPD. The recommended approach for secure and early detection of decryption failure is to encrypt data using v2 SEIPD.
If the session key is public-key encrypted, the quick check is not useful as the If the session key is public key encrypted, the quick check is not useful as the
public-key encryption of the session key should guarantee that it is the right public key encryption of the session key should guarantee that it is the right
session key.</t> session key.</t>
<t>The quick check oracle attack is a particular type of attack that exp
<t>The quick check oracle attack is a particular type of attack that exploits ci loits ciphertext malleability.
phertext malleability.
For information about other similar attacks, see <xref target="ciphertext-mallea bility"/>.</t> For information about other similar attacks, see <xref target="ciphertext-mallea bility"/>.</t>
</section>
</section> <section anchor="pkcs1-errors">
<section anchor="pkcs1-errors"><name>Avoiding Leaks From PKCS#1 Errors</name> <name>Avoiding Leaks from PKCS#1 Errors</name>
<t>The PKCS#1 padding (used in RSA-encrypted and ElGamal-encrypted PKESK
<t>The PKCS#1 padding (used in RSA-encrypted and ElGamal-encrypted PKESK) has be ) has been found to be vulnerable to attacks in which a system that allows disti
en found to be vulnerable to attacks in which a system that allows distinguishin nguishing padding errors from other decryption errors can act as a decryption an
g padding errors from other decryption errors can act as a decryption and/or sig d/or signing oracle that can leak the session key or allow signing arbitrary dat
ning oracle that can leak the session key or allow signing arbitrary data, respe a, respectively <xref target="BLEICHENBACHER-PKCS1"/>.
ctively <xref target="BLEICHENBACHER-PKCS1"/>.
The number of queries required to carry out an attack can range from thousands t o millions, depending on how strict and careful an implementation is in processi ng the padding.</t> The number of queries required to carry out an attack can range from thousands t o millions, depending on how strict and careful an implementation is in processi ng the padding.</t>
<t>To make the attack more difficult, an implementation <bcp14>SHOULD</b
<t>To make the attack more difficult, an implementation <bcp14>SHOULD</bcp14> im cp14> implement strict, robust, and constant time padding checks.</t>
plement strict, robust, constant time padding checks.</t> <t>To prevent the attack, in settings where the attacker does not have a
ccess to timing information concerning message decryption, the simplest solution
<t>To prevent the attack, in settings where the attacker does not have access to is to report a single error code for all variants of PKESK processing errors as
timing information concerning message decryption, the simplest solution is to r well as SEIPD integrity errors (this also includes session key parsing errors,
eport a single error code for all variants of PKESK processing errors as well as such as on an invalid cipher algorithm for v3 PKESK, or a session key size misma
SEIPD integrity errors (this includes also session key parsing errors, such as tch for v6 PKESK). If the attacker may have access to timing information, then a
on invalid cipher algorithm for v3 PKESK, or session key size mismatch for v6 PK constant time solution is also needed. This requires careful design, especially
ESK). for v3 PKESK, where session key size and cipher information is typically not kn
If the attacker may have access to timing information, then a constant time solu own in advance, as it is part of the PKESK encrypted payload.</t>
tion is also needed. </section>
This requires careful design, especially for v3 PKESK, where session key size an <section anchor="fingerprint-usability">
d cipher information is typically not known in advance, as it is part of the PKE <name>Fingerprint Usability</name>
SK encrypted payload.</t> <t>This specification uses fingerprints in several places on the wire (e
.g., Sections <xref target="revocation-key" format="counter"/>, <xref target="is
</section> suer-fingerprint-subpacket" format="counter"/>, and <xref target="intended-recip
<section anchor="fingerprint-usability"><name>Fingerprint Usability</name> ient-fingerprint" format="counter"/>) and in processing (e.g., in ECDH KDF <xref
target="ecdh"/>). An implementation may also use the fingerprint internally, fo
<t>This specification uses fingerprints in several places on the wire (e.g., <xr r example, as an index to a keystore.</t>
ef target="revocation-key"/>, <xref target="issuer-fingerprint-subpacket"/>, and <t>Additionally, some OpenPGP users have historically used manual finger
<xref target="intended-recipient-fingerprint"/>), and in processing (e.g., in E print comparison to verify the public key of a peer.
CDH KDF <xref target="ecdh"/>).
An implementation may also use the fingerprint internally, for example as an ind
ex to a keystore.</t>
<t>Additionally, some OpenPGP users have historically used manual fingerprint co
mparison to verify the public key of a peer.
For a version 4 fingerprint, this has typically been done with the fingerprint r epresented as 40 hexadecimal digits, often broken into groups of four digits wit h whitespace between each group.</t> For a version 4 fingerprint, this has typically been done with the fingerprint r epresented as 40 hexadecimal digits, often broken into groups of four digits wit h whitespace between each group.</t>
<t>When a human is actively involved, the result of such a verification
is dubious.
There is little evidence that most humans are good at precise comparison of high
-entropy data, particularly when that data is represented in compact textual for
m like a hexadecimal <xref target="USENIX-STUDY"/>.</t>
<t>The version 6 fingerprint makes the challenge for a human verifier ev
en worse.
At 256 bits (compared to version 4's 160-bit fingerprint), a version 6 fingerpri
nt is even harder for a human to successfully compare.</t>
<t>An OpenPGP implementation should prioritize mechanical fingerprint tr
ansfer and comparison where possible and <bcp14>SHOULD NOT</bcp14> promote manua
l transfer or comparison of full fingerprints by a human unless there is no othe
r way to achieve the desired result.</t>
<t>While this subsection acknowledges existing practice for human-repres
entable version 4 fingerprints, this document does not attempt to standardize an
y specific human-readable form of version 6 fingerprint for this discouraged use
case.</t>
<t>NOTE: the topic of interoperable human-in-the-loop key verification n
eeds more work, which will be done in a separate document.</t>
</section>
<section anchor="ciphertext-malleability">
<name>Avoiding Ciphertext Malleability</name>
<t>If ciphertext can be modified by an attacker but still subsequently d
ecrypted to some new plaintext, it is considered "malleable". A number of attack
s can arise in any cryptosystem that uses malleable encryption, so <xref target=
"RFC4880"/> and later versions of OpenPGP offer mechanisms to defend against it.
However, OpenPGP data may have been created before these defense mechanisms wer
e available. Because OpenPGP implementations deal with historic stored data, the
y may encounter malleable ciphertexts.</t>
<t>When a human is actively involved, the result of such a verification is dubio <t>When an OpenPGP implementation discovers that it is decrypting data t
us. hat appears to be malleable, it <bcp14>MUST</bcp14> generate a clear error messa
There is little evidence that most humans are good at precise comparison of high ge that indicates the integrity of the message is suspect, it <bcp14>SHOULD NOT<
-entropy data, particularly when that data is represented in compact textual for /bcp14> attempt to parse nor release decrypted data to the user, and it <bcp14>S
m like a hexadecimal (<xref target="USENIX-STUDY"/>).</t> HOULD</bcp14> halt with an error.
Parsing or releasing decrypted data before having confirmed its integrity can le
<t>The version 6 fingerprint makes the challenge for a human verifier even worse ak the decrypted data <xref target="EFAIL"/> <xref target="MRLG15"/>.</t>
. <t>In the case of AEAD encrypted data, if the authentication tag fails t
At 256 bits (compared to v4's 160 bit fingerprint), a v6 fingerprint is even har o verify, the implementation <bcp14>MUST NOT</bcp14> attempt to parse nor releas
der for a human to successfully compare.</t> e decrypted data to the user, and it <bcp14>MUST</bcp14> halt with an error.</t>
<t>An implementation that encounters malleable ciphertext <bcp14>MAY</bc
<t>An OpenPGP implementation should prioritize mechanical fingerprint transfer a p14> choose to release cleartext to the user if it is not encrypted using AEAD,
nd comparison where possible, and <bcp14>SHOULD NOT</bcp14> promote manual trans it is known to be dealing with historic archived legacy data, and the user is aw
fer or comparison of full fingerprints by a human unless there is no other way t are of the risks.</t>
o achieve the desired result.</t> <t>In the case of AEAD encrypted messages, if the message is truncated,
i.e., the final zero-octet chunk and possibly (part of) some chunks before it ar
<t>While this subsection acknowledges existing practice for human-representable e missing, the implementation <bcp14>MAY</bcp14> choose to release cleartext fro
v4 fingerprints, this document does not attempt to standardize any specific huma m the fully authenticated chunks before it to the user if it is operating in a s
n-readable form of v6 fingerprint for this discouraged use case.</t> treaming fashion, but it <bcp14>MUST</bcp14> indicate a clear error message as s
oon as the truncation is detected.</t>
<t>NOTE: the topic of interoperable human-in-the-loop key verification needs mor <t>Any of the following OpenPGP data elements indicate that malleable ci
e work, to be done in a separate document.</t> phertext is present:</t>
<ul spacing="normal">
</section> <li>
<section anchor="ciphertext-malleability"><name>Avoiding Ciphertext Malleability <t>All Symmetrically Encrypted Data packets (<xref target="sed"/>).<
</name> /t>
</li>
<t>If ciphertext can be modified by an attacker but still subsequently decrypted <li>
to some new plaintext, it is considered "malleable". <t>Within any encrypted container, any Compressed Data packet (<xref
A number of attacks can arise in any cryptosystem that uses malleable encryption target="compressed-data"/>) where there is a decompression failure.</t>
, so <xref target="RFC4880"/> and later versions of OpenPGP offer mechanisms to </li>
defend against it. <li>
However, OpenPGP data may have been created before these defense mechanisms were <t>Any version 1 Symmetrically Encrypted and Integrity Protected Dat
available. a packet (<xref target="version-one-seipd"/>) where the internal Modification De
Because OpenPGP implementations deal with historic stored data, they may encount tection Code does not validate.</t>
er malleable ciphertexts.</t> </li>
<li>
<t>When an OpenPGP implementation discovers that it is decrypting data that appe <t>Any version 2 Symmetrically Encrypted and Integrity Protected Dat
ars to be malleable, it <bcp14>MUST</bcp14> indicate a clear error message that a packet (<xref target="version-two-seipd"/>) where the authentication tag of an
the integrity of the message is suspect, <bcp14>SHOULD NOT</bcp14> attempt to pa y chunk fails or where there is no final zero-octet chunk.</t>
rse nor release decrypted data to the user, and <bcp14>SHOULD</bcp14> halt with </li>
an error. <li>
Parsing or releasing decrypted data before having confirmed its integrity can le <t>Any Secret-Key packet with encrypted secret key material (<xref t
ak the decrypted data <xref target="EFAIL"/>, <xref target="MRLG15"/>.</t> arget="secret-key-encryption"/>) where there is an integrity failure, based on t
he value of the secret key protection octet: </t>
<t>In the case of AEAD encrypted data, if the authentication tag fails to verify
, the implementation <bcp14>MUST NOT</bcp14> attempt to parse nor release decryp
ted data to the user, and <bcp14>MUST</bcp14> halt with an error.</t>
<t>An implementation that encounters malleable ciphertext <bcp14>MAY</bcp14> cho
ose to release cleartext to the user if it is not encrypted using AEAD, and it i
s known to be dealing with historic archived legacy data, and the user is aware
of the risks.</t>
<t>In the case of AEAD encrypted messages, if the message is truncated, i.e. the
final zero-octet chunk and possibly (part of) some chunks before it are missing
, the implementation <bcp14>MAY</bcp14> choose to release cleartext from fully a
uthenticated chunks before it to the user if it is operating in a streaming fash
ion, but it <bcp14>MUST</bcp14> indicate a clear error message as soon as the tr
uncation is detected.</t>
<t>Any of the following OpenPGP data elements indicate that malleable ciphertext
is present:</t>
<t><list style="symbols">
<t>All Symmetrically Encrypted Data packets (<xref target="sed"/>).</t>
<t>Within any encrypted container, any Compressed Data packet (<xref target="c
ompressed-data"/>) where there is a decompression failure.</t>
<t>Any version 1 Symmetrically Encrypted Integrity Protected Data packet (<xre
f target="version-one-seipd"/>) where the internal Modification Detection Code d
oes not validate.</t>
<t>Any version 2 Symmetrically Encrypted Integrity Protected Data packet (<xre
f target="version-two-seipd"/>) where the authentication tag of any chunk fails,
or where there is no final zero-octet chunk.</t>
<t>Any Secret-Key packet with encrypted secret key material (<xref target="sec
ret-key-encryption"/>) where there is an integrity failure, based on the value o
f the secret key protection octet: <list style="symbols">
<t>Value 255 (MalleableCFB) or raw cipher algorithm: where the trailing 2-
octet checksum does not match.</t>
<t>Value 254 (CFB): where the SHA1 checksum is mismatched.</t>
<t>Value 253 (AEAD): where the AEAD authentication tag is invalid.</t>
</list></t>
</list></t>
<t>To avoid these circumstances, an implementation that generates OpenPGP encryp <ul spacing="normal">
ted data <bcp14>SHOULD</bcp14> select the encrypted container format with the mo <li>
st robust protections that can be handled by the intended recipients. <t>Value 253 (AEAD): where the AEAD authentication tag is invali
d.</t>
</li>
<li>
<t>Value 254 (CFB): where the SHA1 checksum is mismatched.</t>
</li>
<li>
<t>Value 255 (MalleableCFB) or raw cipher algorithm: where the t
railing 2-octet checksum does not match.</t>
</li>
</ul>
</li>
</ul>
<t>To avoid these circumstances, an implementation that generates OpenPG
P encrypted data <bcp14>SHOULD</bcp14> select the encrypted container format wit
h the most robust protections that can be handled by the intended recipients.
In particular:</t> In particular:</t>
<ul spacing="normal">
<t><list style="symbols"> <li>
<t>The SED packet is deprecated, and <bcp14>MUST NOT</bcp14> be generated.</t> <t>The SED packet is deprecated and <bcp14>MUST NOT</bcp14> be gener
<t>When encrypting to one or more public keys: <list style="symbols"> ated.</t>
<t>If all recipient keys indicate support for version 2 of the Symmetrical </li>
ly Encrypted Integrity Protected Data packet in their Features subpacket (<xref <li>
target="features-subpacket"/>), or are v6 keys without a Features subpacket, or <t>When encrypting to one or more public keys: </t>
the implementation can otherwise infer that all recipients support v2 SEIPD pack <ul spacing="normal">
ets, the implementation <bcp14>SHOULD</bcp14> encrypt using a v2 SEIPD packet.</ <li>
t> <t>If all recipient keys indicate support for a version 2 Symmet
<t>If one of the recipients does not support v2 SEIPD packets, then the me rically Encrypted and Integrity Protected Data packet in their Features signatur
ssage generator <bcp14>MAY</bcp14> use a v1 SEIPD packet instead.</t> e subpacket (<xref target="features-subpacket"/>), if all recipient keys are ver
</list></t> sion 6 keys without a Features signature subpacket, or the implementation can ot
<t>Passphrase-protected secret key material in a v6 Secret Key or v6 Secret Su herwise infer that all recipients support v2 SEIPD packets, the implementation <
bkey packet <bcp14>SHOULD</bcp14> be protected with AEAD encryption (S2K usage o bcp14>SHOULD</bcp14> encrypt using a v2 SEIPD packet.</t>
ctet 253) unless it will be transferred to an implementation that is known to no </li>
t support AEAD. <li>
An implementation should be aware that, in scenarios where an attacker has write <t>If one of the recipients does not support v2 SEIPD packets, t
access to encrypted private keys, CFB-encrypted keys (S2K usage octet 254 or 25 hen the message generator <bcp14>MAY</bcp14> use a v1 SEIPD packet instead.</t>
5) are vulnerable to corruption attacks that can cause leakage of secret data wh </li>
en the secret key is used <xref target="KOPENPGP"/>, <xref target="KR02"/>.</t> </ul>
</list></t> </li>
<li>
<t>Implementers should implement AEAD (v2 SEIPD and S2K usage octet 253) promptl <t>Passphrase-protected secret key material in a version 6 Secret Ke
y and encourage its spread.</t> y or version 6 Secret Subkey packet <bcp14>SHOULD</bcp14> be protected with AEAD
encryption (S2K usage octet 253) unless it will be transferred to an implementa
<t>Users are <bcp14>RECOMMENDED</bcp14> to migrate to AEAD.</t> tion that is known to not support AEAD.
An implementation should be aware that, in scenarios where an attacker has write
</section> access to encrypted private keys, CFB-encrypted keys (S2K usage octet 254 or 25
<section anchor="secure-sessionkey-reuse"><name>Secure Use of the v2 SEIPD Sessi 5) are vulnerable to corruption attacks that can cause leakage of secret data wh
on-Key-Reuse Feature</name> en the secret key is used <xref target="KOPENPGP"/> <xref target="KR02"/>.</t>
</li>
<t>The salted key derivation of v2 SEIPD packets (<xref target="version-two-seip </ul>
d"/>) allows the recipient of an encrypted message to reply to the sender and al <t>Implementers should implement AEAD (v2 SEIPD and S2K usage octet 253)
l other recipients without needing their public keys but by using the same v6 PK promptly and encourage its spread.</t>
ESK packets he received and a different random salt value. <t>Users are <bcp14>RECOMMENDED</bcp14> to migrate to AEAD.</t>
This ensures a secure mechanism on the cryptographic level that enables the use </section>
of message encryption in cases where a sender does not have a copy of an encrypt <section anchor="secure-sessionkey-reuse">
ion-capable certificate for one or more participants in the conversation and thu <name>Secure Use of the v2 SEIPD Session-Key-Reuse Feature</name>
s can enhance the overall security of an application. <t>The salted key derivation of v2 SEIPD packets (<xref target="version-
However, care must be taken when using this mechanism not to create security vul two-seipd"/>) allows the recipient of an encrypted message to reply to the sende
nerabilities, such as the following.</t> r and all other recipients without needing their public keys but by using the sa
me v6 PKESK packets it received and a different random salt value.
<t><list style="symbols"> This ensures a secure mechanism on the cryptographic level that enables the use
<t>Replying to only a subset of the original recipients and the original sende of message encryption in cases where a sender does not have a copy of an encrypt
r by use of the session-key-reuse feature would mean that the remaining recipien ion-capable certificate for one or more participants in the conversation and thu
ts (including the sender) of the original message could read the encrypted reply s can enhance the overall security of an application. However, care must be take
message, too.</t> n when using this mechanism not to create security vulnerabilities, such as the
<t>Adding a further recipient to the reply that is encrypted using the session following:</t>
-key-reuse feature gives that further recipient also cryptographic access to the <ul spacing="normal">
original message that is being replied to (and potentially to a longer history <li>
of previous messages).</t> <t>Replying to only a subset of the original recipients and the orig
<t>A modification of the list of recipients addressed in the above points need inal sender by use of the session-key-reuse feature would mean that the remainin
s also to be safeguarded when a message is initially composed as a reply with se g recipients (including the sender) of the original message could read the encry
ssion-key reuse but then first stored (e.g. as a draft) and later reopened for f pted reply message, too.</t>
urther editing and finally sent.</t> </li>
<t>There is the potential threat that an attacker with network or mailbox acce <li>
ss, who is at the same time a recipient of the original message, silently remove <t>Adding a further recipient to the reply that is encrypted using t
s themselves from the message before the victim's client receives it. he session-key-reuse feature gives that further recipient also cryptographic acc
ess to the original message that is being replied to (and potentially to a longe
r history of previous messages).</t>
</li>
<li>
<t>A modification of the list of recipients addressed in the above p
oints also needs to be safeguarded when a message is initially composed as a rep
ly with session-key reuse but then is stored (e.g., as a draft) and later reopen
ed for further editing and to be finally sent.</t>
</li>
<li>
<t>There is the potential threat that an attacker with network or ma
ilbox access, who is at the same time a recipient of the original message, silen
tly removes themselves from the message before the victim's client receives it.
The victim's client that then uses the mechanism for replying with session-key r euse would unknowingly compose an encrypted message that could be read by the at tacker. The victim's client that then uses the mechanism for replying with session-key r euse would unknowingly compose an encrypted message that could be read by the at tacker.
Implementations are encouraged to use the Intended Recipient Fingerprint (<xref Implementations are encouraged to use the Intended Recipient Fingerprint subpack
target="intended-recipient-fingerprint"/>) subpacket when composing messages and et (<xref target="intended-recipient-fingerprint"/>) when composing messages and
to use it to check the consistency of the set of recipients of a message before checking the consistency of the set of recipients of a message before replying
replying to it with session-key reuse.</t> to it with session-key reuse.</t>
<t>When using the session-key-reuse feature in any higher-layer protocol, care </li>
should be taken that there is no other potentially interfering practice of sess <li>
ion-key reuse established in that protocol. <t>When using the session-key-reuse feature in any higher-layer proto
Such interfering session-key reuse could for instance be given if an initial mes col, care should be taken to ensure that there is no other potentially interferi
sage is already composed by reusing the session key of an existing encrypted fil ng practice of session-key reuse established in that protocol. Such interfering
e the access to which may be shared among a group of users already. session-key reuse could, for instance, be given -- if an initial message is alre
Using the session-key-reuse feature to compose an encrypted reply to such a mess ady composed -- by reusing the session key of an existing encrypted file that ma
age would unknowingly give this whole group of users cryptographic access to the y have been shared among a group of users already. Using the session-key-reuse f
encrypted message.</t> eature to compose an encrypted reply to such a message would unknowingly give th
<t>Generally, the use of the session-key-reuse feature should be under the con is whole group of users cryptographic access to the encrypted message.</t>
trol of the user. </li>
Specifically, care should be taken that this feature is not silently used when t <li>
he user assumes that proper public-key encryption is used. <t>Generally, the use of the session-key-reuse feature should be und
This can be the case for instance when the public key of one of the recipients o er the control of the user. Specifically, care should be taken so that this feat
f the reply is known but has expired. ure is not silently used when the user assumes that proper public key encryption
Special care should be taken to ensure that users do not get caught in continued is used. This can be the case, for instance, when the public key of one of the
use of the session-key reuse unknowingly but instead receive the chance to swit recipients of the reply is known but has expired. Special care should be taken t
ch to proper fresh public-key encryption as soon as possible.</t> o ensure that users do not get caught in continued use of the session-key reuse
<t>Whenever possible, a client should prefer a fresh public key encryption ove unknowingly but instead receive the chance to switch to proper fresh public key
r the session-key reuse.</t> encryption as soon as possible.</t>
</list></t> </li>
<li>
<t>Even though this not necessarily being a security aspect, note that initially <t>Whenever possible, a client should prefer a fresh public key encr
composing an encrypted reply using the session-key-reuse feature on one client yption over the session-key reuse.</t>
and storing it (e.g. as a draft) and later reopening the stored unfinished reply </li>
with another client that does not support the session-key-reuse feature may lea </ul>
d to interoperability problems.</t> <t>Even though this is not necessarily a security aspect, note that init
ially composing an encrypted reply using the session-key-reuse feature on one cl
<t>Avoiding the pitfalls described above requires context-specific expertise. ient and then storing it (e.g., as a draft) and later reopening the stored unfin
ished reply with another client that does not support the session-key-reuse feat
ure may lead to interoperability problems.</t>
<t>Avoiding the pitfalls described above requires context-specific exper
tise.
An implementation should only make use of the session-key-reuse feature in any p articular application layer when it can follow reasonable documentation about ho w to deploy the feature safely in the specific application. An implementation should only make use of the session-key-reuse feature in any p articular application layer when it can follow reasonable documentation about ho w to deploy the feature safely in the specific application.
At the time of this writing, there is no known documentation about safe reuse of OpenPGP session keys for any specific context. An implementer that intends to m ake use of this feature should publish their own proposed guidance for others to review.</t> At the time of this writing, there is no known documentation about safe reuse of OpenPGP session keys for any specific context. An implementer that intends to m ake use of this feature should publish their own proposed guidance for others to review.</t>
</section>
</section> <section anchor="escrowed-revocations">
<section anchor="escrowed-revocations"><name>Escrowed Revocation Signatures</nam <name>Escrowed Revocation Signatures</name>
e> <t>A keyholder, Alice, may wish to designate a third party to be able to
revoke her own key.</t>
<t>A keyholder, Alice, may wish to designate a third party to be able to revoke <t>The preferred way for Alice to do this is to produce a specific Revoc
Alice's own key.</t> ation Signature (Signature Type ID 0x20, 0x28, or 0x30) and distribute it secure
ly to a preferred revoker who can hold it in escrow. The preferred revoker can t
<t>The preferred way for her to do this is to produce a specific Revocation Sign hen publish the escrowed Revocation Signature at whatever time is deemed appropr
ature (signature type IDs 0x20, 0x28, or 0x30) and distribute it securely to her iate rather than generating the Revocation Signature themselves.</t>
preferred revoker who can hold it in escrow. <t>There are multiple advantages of using an escrowed Revocation Signatu
The preferred revoker can then publish the escrowed Revocation Signature at what re over the deprecated Revocation Key subpacket (<xref target="revocation-key"/>
ever time is deemed appropriate, rather than generating a revocation signature t ):</t>
hemselves.</t> <ul spacing="normal">
<li>
<t>There are multiple advantages of using an escrowed Revocation Signature over <t>The keyholder can constrain what types of revocation the preferre
the deprecated Revocation Key subpacket (<xref target="revocation-key"/>):</t> d revoker can issue, by only escrowing those specific signatures.</t>
</li>
<t><list style="symbols"> <li>
<t>The keyholder can constrain what types of revocation the preferred revoker <t>There is no public/visible linkage between the keyholder and the
can issue, by only escrowing those specific signatures.</t> preferred revoker.</t>
<t>There is no public/visible linkage between the keyholder and the preferred </li>
revoker.</t> <li>
<t>Third parties can verify the revocation without needing to find the key of <t>Third parties can verify the revocation without needing to find t
the preferred revoker.</t> he key of the preferred revoker.</t>
<t>The preferred revoker doesn't even need to have a public OpenPGP key if som </li>
e other secure transport is possible between them and the keyholder.</t> <li>
<t>Implementation support for enforcing a revocation from an authorized Revoca <t>The preferred revoker doesn't even need to have a public OpenPGP
tion Key subpacket is uneven and unreliable.</t> Key if some other secure transport is possible between them and the keyholder.</
<t>If the fingerprint mechanism suffers a cryptanalytic flaw, the escrowed Rev t>
ocation Signature is not affected.</t> </li>
</list></t> <li>
<t>Implementation support for enforcing a revocation from an authori
<t>A Revocation Signature may also be split up into shares and distributed among zed Revocation Key subpacket is uneven and unreliable.</t>
multiple parties, requiring some subset of those parties to collaborate before </li>
the escrowed Revocation Signature is recreated.</t> <li>
<t>If the fingerprint mechanism suffers a cryptanalytic flaw, the es
</section> crowed Revocation Signature is not affected.</t>
<section anchor="CSPRNG"><name>Random Number Generation and Seeding</name> </li>
</ul>
<t>OpenPGP requires a cryptographically secure pseudorandom number generator (CS <t>A Revocation Signature may also be split up into shares and distribut
PRNG). ed among multiple parties, requiring some subset of those parties to collaborate
In most cases, the operating system provides an appropriate facility such as a < before the escrowed Revocation Signature is recreated.</t>
spanx style="verb">getrandom()</spanx> syscall on Linux or BSD, which should be </section>
used absent other (for example, performance) concerns. <section anchor="CSPRNG">
It is <bcp14>RECOMMENDED</bcp14> to use an existing CSPRNG implementation in pre <name>Random Number Generation and Seeding</name>
ference to crafting a new one. <t>OpenPGP requires a cryptographically secure pseudorandom number gener
Many adequate cryptographic libraries are already available under favorable lice ator (CSPRNG). In most cases, the operating system provides an appropriate facil
nse terms. ity such as a <tt>getrandom()</tt> syscall on Linux or BSD, which should be used
Should those prove unsatisfactory, <xref target="RFC4086"/> provides guidance on absent other (for example, performance) concerns.
the generation of random values.</t> It is <bcp14>RECOMMENDED</bcp14> to use an existing CSPRNG implementation as opp
osed to crafting a new one.
<t>OpenPGP uses random data with three different levels of visibility:</t> Many adequate cryptographic libraries are already available under favorable lice
nse terms. Should those prove unsatisfactory, <xref target="RFC4086"/> provides
<t><list style="symbols"> guidance on the generation of random values.</t>
<t>In publicly-visible fields such as nonces, IVs, public padding material, or <t>OpenPGP uses random data with three different levels of visibility:</
salts,</t> t>
<t>In shared-secret values, such as session keys for encrypted data or padding <ul spacing="normal">
material within an encrypted packet, and</t> <li>
<t>In entirely private data, such as asymmetric key generation.</t> <t>In publicly visible fields such as nonces, IVs, public padding ma
</list></t> terial, or salts.</t>
</li>
<t>With a properly functioning CSPRNG, this range of visibility does not present <li>
a security problem, as it is not feasible to determine the CSPRNG state from it <t>In shared-secret values, such as session keys for encrypted data
s output. or padding material within an encrypted packet.</t>
</li>
<li>
<t>In entirely private data, such as asymmetric key generation.</t>
</li>
</ul>
<t>With a properly functioning CSPRNG, this range of visibility does not
present a security problem, as it is not feasible to determine the CSPRNG state
from its output.
However, with a broken CSPRNG, it may be possible for an attacker to use visible output to determine the CSPRNG internal state and thereby predict less-visible data like keying material, as documented in <xref target="CHECKOWAY"/>.</t> However, with a broken CSPRNG, it may be possible for an attacker to use visible output to determine the CSPRNG internal state and thereby predict less-visible data like keying material, as documented in <xref target="CHECKOWAY"/>.</t>
<t>An implementation can provide extra security against this form of att
<t>An implementation can provide extra security against this form of attack by u ack by using separate CSPRNGs to generate random data with different levels of v
sing separate CSPRNGs to generate random data with different levels of visibilit isibility.</t>
y.</t> </section>
<section anchor="traffic-analysis">
</section> <name>Traffic Analysis</name>
<section anchor="traffic-analysis"><name>Traffic Analysis</name> <t>When sending OpenPGP data through the network, the size of the data m
ay leak information to an attacker. There are circumstances where such a leak co
<t>When sending OpenPGP data through the network, the size of the data may leak uld be unacceptable from a security perspective.</t>
information to an attacker. <t>For example, if possible cleartext messages for a given protocol are
There are circumstances where such a leak could be unacceptable from a security known to be either <tt>yes</tt> (3 octets) or <tt>no</tt> (2 octets) and the mes
perspective.</t> sages are sent within a Symmetrically Encrypted and Integrity Protected Data pac
ket, the length of the encrypted message will reveal the contents of the clearte
<t>For example, if possible cleartext messages for a given protocol are known to xt.</t>
be either <spanx style="verb">yes</spanx> (three octets) and <spanx style="verb <t>In another example, sending an OpenPGP Transferable Public Key over a
">no</spanx> (two octets) and the messages are sent within a Symmetrically-Encry n encrypted network connection might reveal the length of the certificate. Since
pted Integrity Protected Data packet, the length of the encrypted message will r the length of an OpenPGP certificate varies based on the content, an external o
eveal the contents of the cleartext.</t> bserver interested in metadata (e.g., which individual is trying to contact anot
her individual) may be able to guess the identity of the certificate sent, if it
<t>In another example, sending an OpenPGP Transferable Public Key over an encryp s length is unique.</t>
ted network connection might reveal the length of the certificate. <t>In both cases, an implementation can adjust the size of the compound
Since the length of an OpenPGP certificate varies based on the content, an exter structure by including a Padding packet (see <xref target="padding-packet"/>).</
nal observer interested in metadata (who is trying to contact whom) may be able t>
to guess the identity of the certificate sent, if its length is unique.</t> </section>
<section anchor="surreptitious-forwarding">
<t>In both cases, an implementation can adjust the size of the compound structur <name>Surreptitious Forwarding</name>
e by including a Padding packet (see <xref target="padding-packet"/>).</t> <t>When an attacker obtains a signature for some text, e.g., by receivin
g a signed message, they may be able to use that signature maliciously by sendin
</section> g a message purporting to come from the original sender, with the same body and
<section anchor="surreptitious-forwarding"><name>Surreptitious Forwarding</name> signature, to a different recipient.
To prevent this, an implementation <bcp14>SHOULD</bcp14> implement the Intended
<t>When an attacker obtains a signature for some text, e.g. by receiving a signe Recipient Fingerprint subpacket (<xref target="intended-recipient-fingerprint"/>
d message, they may be able to use that signature maliciously by sending a messa ).</t>
ge purporting to come from the original sender, with the same body and signature </section>
, to a different recipient. <section anchor="subpacket-section-guidance">
To prevent this, an implementation <bcp14>SHOULD</bcp14> implement the Intended <name>Hashed vs. Unhashed Subpackets</name>
Recipient Fingerprint signature subpacket (<xref target="intended-recipient-fing <t>Each OpenPGP signature can have subpackets in two different sections.
erprint"/>).</t>
</section>
<section anchor="subpacket-section-guidance"><name>Hashed vs. Unhashed Subpacket
s</name>
<t>Each OpenPGP signature can have subpackets in two different sections.
The first set of subpackets (the "hashed section") is covered by the signature i tself. The first set of subpackets (the "hashed section") is covered by the signature i tself.
The second set has no cryptographic protections, and is used for advisory materi The second set has no cryptographic protections and is used for advisory materia
al only, including locally-stored annotations about the signature.</t> l only, including locally stored annotations about the signature.</t>
<t>For example, consider an implementation working with a specific signa
<t>For example, consider an implementation working with a specific signature tha ture that happens to know that the signature was made by a certain key, even tho
t happens to know that the signature was made by a certain key, even though the ugh the signature contains no Issuer Fingerprint subpacket (<xref target="issuer
signature contains no Issuer Fingerprint subpacket (<xref target="issuer-fingerp -fingerprint-subpacket"/>) in the hashed section.
rint-subpacket"/>) in the hashed section. That implementation <bcp14>MAY</bcp14> synthesize an Issuer Fingerprint subpacke
That implementation <bcp14>MAY</bcp14> synthesize an Issuer Fingerprint subpacke t and store it in the unhashed section so that it will be able to recall which k
t and store it in the unhashed section so that in the future it will be able to ey issued the signature in the future.</t>
recall which key issued the signature.</t> <t>Some subpackets are only useful when they are in the hashed section,
and an implementation <bcp14>SHOULD</bcp14> ignore them when they are found with
<t>Some subpackets are only useful when they are in the hashed section, and an i unknown provenance in the unhashed section.
mplementation <bcp14>SHOULD</bcp14> ignore them when they are found with unknown For example, a Preferred AEAD Ciphersuites subpacket (<xref target="preferred-v2
provenance in the unhashed section. -seipd"/>) in a Direct Key self-signature indicates the preferences of the keyho
For example, a Preferred AEAD Ciphersuites subpacket (<xref target="preferred-v2 lder when encrypting v2 SEIPD data to the key.
-seipd"/>) in a direct key self-signature indicates the preferences of the keyho
lder when encrypting SEIPD v2 data to the key.
An implementation that observes such a subpacket found in the unhashed section w ould open itself to an attack where the recipient's certificate is tampered with to encourage the use of a specific cipher or mode of operation.</t> An implementation that observes such a subpacket found in the unhashed section w ould open itself to an attack where the recipient's certificate is tampered with to encourage the use of a specific cipher or mode of operation.</t>
</section>
</section> <section anchor="compress-bomb">
<section anchor="compress-bomb"><name>Malicious Compressed Data</name> <name>Malicious Compressed Data</name>
<t>It is possible to form a compression quine that produces itself upon
<t>It is possible to form a compression quine that produces itself upon decompre decompression, leading to infinite regress in any implementation willing to pars
ssion, leading to infinite regress in any implementation willing to parse arbitr e arbitrary numbers of layers of compression. This could cause resource exhausti
ary numbers of layers of compression. on, which itself could lead to termination by the operating system. If the opera
This could cause resource exhaustion which itself could lead to it being termina ting system creates a "crash report", that report could contain confidential inf
ted by the operating system. ormation.</t>
If the operating system would create a "crash report", that report could contain <t>An OpenPGP implementation <bcp14>SHOULD</bcp14> limit the number of l
confidential information.</t> ayers of compression it is willing to decompress in a single message.</t>
</section>
<t>An OpenPGP implementation <bcp14>SHOULD</bcp14> limit the number of layers of </section>
compression it is willing to decompress in a single message.</t> <section anchor="implementation-considerations">
<name>Implementation Considerations</name>
</section> <t>This section is a collection of comments to help an implementer who has
</section> a particular interest in backward compatibility. Often the differences are smal
<section anchor="implementation-considerations"><name>Implementation Considerati l, but small differences are frequently more vexing than large differences. Thus
ons</name> , this is a non-comprehensive list of potential problems and gotchas for a devel
oper who is trying to achieve backward compatibility.</t>
<t>This section is a collection of comments to help an implementer, particularly <ul spacing="normal">
with an eye to backward compatibility. <li>
Often the differences are small, but small differences are frequently more vexin <t>There are many possible ways for two keys to have the same key mate
g than large differences. rial but different fingerprints (and thus different Key IDs). For example, since
Thus, this is a non-comprehensive list of potential problems and gotchas for a d a version 4 fingerprint is constructed by hashing the key creation time along w
eveloper who is trying to be backward-compatible.</t> ith other things, two version 4 keys created at different times yet with the sam
e key material will have different fingerprints.</t>
<t><list style="symbols"> </li>
<t>There are many ways possible for two keys to have the same key material, bu <li>
t different fingerprints (and thus Key IDs). <t>OpenPGP does not put limits on the size of public keys.
For example, since a v4 fingerprint is constructed by hashing the key creation t
ime along with other things, two v4 keys created at different times, yet with th
e same key material will have different fingerprints.</t>
<t>OpenPGP does not put limits on the size of public keys.
However, larger keys are not necessarily better keys. However, larger keys are not necessarily better keys.
Larger keys take more computation time to use, and this can quickly become impra ctical. Larger keys take more computation time to use, and this can quickly become impra ctical.
Different OpenPGP implementations may also use different upper bounds for public Different OpenPGP implementations may also use different upper bounds for public
key sizes, and so care should be taken when choosing sizes to maintain interope key sizes, so care should be taken when choosing sizes to maintain interoperabi
rability.</t> lity.</t>
<t>ASCII armor is an optional feature of OpenPGP. </li>
The OpenPGP working group strives for a minimal set of mandatory-to-implement fe <li>
atures, and since there could be useful implementations that only use binary obj <t>ASCII Armor is an optional feature of OpenPGP.
ect formats, this is not a "<bcp14>MUST</bcp14>" feature for an implementation. The OpenPGP Working Group strives for a minimal set of mandatory-to-implement fe
For example, an implementation that is using OpenPGP as a mechanism for file sig atures, and since there could be useful implementations that only use binary obj
natures may find ASCII armor unnecessary. ect formats, this is not a "<bcp14>MUST</bcp14>" feature for an implementation.
OpenPGP permits an implementation to declare what features it does and does not For example, an implementation that is using OpenPGP as a mechanism for file sig
support, but ASCII armor is not one of these. natures may find ASCII Armor unnecessary.
Since most implementations allow binary and armored objects to be used indiscrim OpenPGP permits an implementation to declare what features it does and does not
inately, an implementation that does not implement ASCII armor may find itself w support, but ASCII Armor is not one of these.
ith compatibility issues with general-purpose implementations. Since most implementations allow binary and armored objects to be used indiscrim
Moreover, implementations of OpenPGP-MIME <xref target="RFC3156"/> already have inately, an implementation that does not implement ASCII Armor may find itself w
a requirement for ASCII armor so those implementations will necessarily have sup ith compatibility issues with general-purpose implementations.
port.</t> Moreover, implementations of OpenPGP-MIME <xref target="RFC3156"/> already have
<t>What this document calls Legacy packet format <xref target="legacy-packet-f a requirement for ASCII Armor, so those implementations will necessarily have su
ormat"/> is what older documents called the "old packet format". pport.</t>
</li>
<li>
<t>What this document calls the "Legacy packet format" (<xref target="
legacy-packet-format"/>) is what older documents called the "old packet format".
It is the packet format used by implementations predating <xref target="RFC2440" />. It is the packet format used by implementations predating <xref target="RFC2440" />.
Older RFCs called the current OpenPGP packet format <xref target="openpgp-packet The current "OpenPGP packet format" (<xref target="openpgp-packet-format"/>) was
-format"/> the "new packet format". called the "new packet format" by older RFCs. This is the format introduced in
This is the format introduced in <xref target="RFC2440"/> and maintained through <xref target="RFC2440"/> and maintained through <xref target="RFC4880"/> to this
<xref target="RFC4880"/> to this document.</t> document.</t>
</list></t> </li>
</ul>
<section anchor="constrained-legacy-fingerprint-storage-for-v6-keys"><name>Const <section anchor="constrained-legacy-fingerprint-storage-for-v6-keys">
rained Legacy Fingerprint Storage for v6 Keys</name> <name>Constrained Legacy Fingerprint Storage for Version 6 Keys</name>
<t>Some OpenPGP implementations have fixed length constraints for key fi
<t>Some OpenPGP implementations have fixed length constraints for key fingerprin ngerprint storage that will not fit all 32 octets of a version 6 fingerprint.
t storage that will not fit all 32 octets of a v6 fingerprint.
For example, <xref target="OPENPGPCARD"/> reserves 20 octets for each stored fin gerprint.</t> For example, <xref target="OPENPGPCARD"/> reserves 20 octets for each stored fin gerprint.</t>
<t>An OpenPGP implementation <bcp14>MUST NOT</bcp14> attempt to map any
part of a version 6 fingerprint to such a constrained field unless the relevant
specification for the constrained environment has explicit guidance for storing
a version 6 fingerprint that distinguishes it from a version 4 fingerprint. An i
mplementation interacting with such a constrained field <bcp14>SHOULD</bcp14> di
rectly calculate the version 6 fingerprint from public key material and associat
ed metadata instead of relying on the constrained field.</t>
</section>
</section>
<section anchor="iana-considerations">
<t>An OpenPGP implementation <bcp14>MUST NOT</bcp14> attempt to map any part of <name>IANA Considerations</name>
a v6 fingerprint to such a constrained field unless the relevant spec for the co <t>This document obsoletes <xref target="RFC4880"/>. IANA has updated all
nstrained environment has explicit guidance for storing a v6 fingerprint that di registration information that references <xref target="RFC4880"/> to reference t
stinguishes it from a v4 fingerprint. his RFC instead.</t>
An implementation interacting with such a constrained field <bcp14>SHOULD</bcp14 <section anchor="rename-pretty-good-privacy-pgp-protocol-group-to-openpgp"
> directly calculate the v6 fingerprint from public key material and associated >
metadata instead of relying on the constrained field.</t> <name>Renamed Protocol Group</name>
<t>IANA bundles a set of registries associated with a particular protoco
</section> l into a "protocol group". IANA has updated the name of the "Pretty Good Privacy
</section> (PGP)" protocol group (i.e., the group of registries described at <eref target=
<section anchor="iana-considerations"><name>IANA Considerations</name> "https://www.iana.org/assignments/pgp-parameters" brackets="angle"/>) to "OpenPG
P". IANA has arranged a permanent redirect from the existing URL to the new URL
<t>This document obsoletes <xref target="RFC4880"/>. for the registries in this protocol group. All further updates specified below a
IANA is requested to update all registration information that references <xref t re for registries within this same OpenPGP protocol group.</t>
arget="RFC4880"/> to instead reference this RFC.</t> </section>
<section anchor="registries-to-be-renamed-and-updated">
<section anchor="rename-pretty-good-privacy-pgp-protocol-group-to-openpgp"><name <name>Renamed and Updated Registries</name>
>Rename "Pretty Good Privacy (PGP)" Protocol Group to "OpenPGP"</name> <!-- tab 1 ok -->
<t>IANA has renamed the "PGP String-to-Key (S2K)" registry to "OpenPGP S
<t>IANA bundles a set of registries associated with a particular protocol into a tring-to-Key (S2K) Types" and updated its contents as shown in <xref target="s2
"protocol group". k-types-registry"/>.</t>
This document requests IANA to update the name of the "Pretty Good Privacy (PGP)
" protocol group (i.e., the group of registries described at <spanx style="verb"
>https://www.iana.org/assignments/pgp-parameters/</spanx>) to "OpenPGP".
If renaming the protocol group results in new URLs for the registries in this pr
otocol group, please arrange for a permanent redirection (e.g., HTTP 301) from t
he existing URLs to the new URLs.
All further updates specified below are for registries within this same "OpenPGP
" protocol group.</t>
</section>
<section anchor="registries-to-be-renamed-and-updated"><name>Registries to be Re
named and Updated</name>
<t>IANA is requested to rename the "PGP String-to-Key (S2K)" registry to "OpenPG
P String-to-Key (S2K) Types" and update its content to <xref target="s2k-types-r
egistry"/>.</t>
<t>IANA is requested to rename the "PGP Packet Types/Tags" registry to "OpenPGP
Packet Types" and update its content to <xref target="packet-types-registry"/>.<
/t>
<t>IANA is requested to rename the "PGP User Attribute Types" registry to "OpenP
GP User Attribute Subpacket Types" and update its content to <xref target="user-
attr-subpacket-types-registry"/>.</t>
<t>IANA is requested to rename the "Image Format Subpacket Types" registry to "O
penPGP Image Attribute Encoding Format" and update its content to <xref target="
image-attr-encoding-format-registry"/>.</t>
<t>IANA is requested to rename the "Key Server Preference Extensions" registry t
o "OpenPGP Key Server Preference Flags" and update its contents to <xref target=
"key-server-preference-flags-registry"/>.</t>
<t>IANA is requested to rename the "Reason for Revocation Extensions" registry t
o "OpenPGP Reason for Revocation Code" and update its contents to <xref target="
reason-for-revocation-code-registry"/>.</t>
<t>IANA is requested to rename the "Key Flags Extensions" registry to "OpenPGP K
ey Flags" and update its contents to <xref target="key-flags-registry"/>.</t>
<t>IANA is requested to rename the "Implementation Features" registry to "OpenPG
P Features Flags" and update its contents to <xref target="features-flags-regist
ry"/>.</t>
<t>IANA is requested to rename the "Public Key Algorithms" registry to "OpenPGP
Public Key Algorithms" and update its contents to <xref target="pubkey-algo-regi
stry"/>.</t>
<t>IANA is requested to rename the "Symmetric Key Algorithms" registry to "OpenP
GP Symmetric Key Algorithms" and update its contents to <xref target="symkey-alg
orithms-registry"/>.</t>
<t>IANA is requested to rename the "Compression Algorithms" registry to "OpenPGP
Compression Algorithms" and update its contents to <xref target="compression-al
gorithms-registry"/>.</t>
<t>IANA is requested to rename the "Hash Algorithms" registry to "OpenPGP Hash A
lgorithms" and update its contents to <xref target="hash-algorithms-registry"/>.
</t>
<t>IANA is requested to rename the "Signature Subpacket Types" registry to "Open
PGP Signature Subpacket Types" and update its contents to <xref target="signatur
e-subpacket-types-registry"/>.</t>
</section> <!-- tab 3 ok -->
<section anchor="removed-registries"><name>Registries to be Removed</name> <t>IANA has renamed the "PGP Packet Types/Tags" registry to "OpenPGP Packet Type
s" and updated its contents as shown in <xref target="packet-types-registry"/>.<
/t>
<t>IANA is requested to remove the empty "New Packet Versions" registry.</t> <!-- tab 5 ok -->
<t>IANA has renamed the "Signature Subpacket Types" registry to "OpenPGP
Signature Subpacket Types" and updated its contents as shown in <xref target="s
ignature-subpacket-types-registry"/>.</t>
<t>A tombstone note should be added to the OpenPGP protocol group with the follo <!-- tab 8 ok -->
wing content: Those wishing to use the removed "New Packet Versions" registry sh <t>IANA has renamed the "Key Server Preference Extensions" registry to "OpenPGP
ould instead register new versions of the relevant packets in the "OpenPGP Key a Key Server Preference Flags" and updated its contents as shown in <xref target="
nd Signature Versions", "OpenPGP Key ID and Fingerprint" and "OpenPGP Encrypted key-server-preference-flags-registry"/>.</t>
Message Packet Versions" registries.</t>
</section> <!-- tab 9 ok -->
<section anchor="added-registries"><name>Registries to be Added</name> <t>IANA has renamed the "Key Flags Extensions" registry to "OpenPGP Key
Flags" and updated its contents as shown in <xref target="key-flags-registry"/>.
</t>
<t>IANA is requested to add the following registries in the OpenPGP protocol gro <!-- tab 10 ok -->
up:</t> <t>IANA has renamed the "Reason for Revocation Extensions" registry to "OpenPGP
Reason for Revocation (Revocation Octet)" and updated its contents as shown in <
xref target="reason-for-revocation-code-registry"/>.</t>
<t><list style="symbols"> <!-- tab 11 ok -->
<t>OpenPGP Secret Key Encryption (S2K Usage Octet) containing <xref target="se <t>IANA has renamed the "Implementation Features" registry to "OpenPGP F
cret-key-protection-registry"/>.</t> eatures Flags" and updated its contents as shown in <xref target="features-flags
<t>OpenPGP Signature Types containing <xref target="signature-types-registry"/ -registry"/>.</t>
>.</t>
<t>OpenPGP Signature Notation Data Subpacket Notation Flags containing <xref t
arget="sig-note-data-note-flags-registry"/>.</t>
<t>OpenPGP Signature Notation Data Subpacket Types containing <xref target="si
g-note-data-subpacket-types"/>.</t>
<t>OpenPGP Key ID and Fingerprint containing <xref target="key-id-fingerprint-
registry"/>.</t>
<t>OpenPGP Image Attribute Version containing <xref target="image-attribute-ve
rsion-registry"/>.</t>
<t>OpenPGP Armor Header Line containing <xref target="armor-header-line-regist
ry"/>.</t>
<t>OpenPGP Armor Header Key containing <xref target="armor-header-key-registry
"/>.</t>
<t>OpenPGP ECC Curve OID and Usage containing <xref target="ecc-oid-usage-regi
stry"/>.</t>
<t>OpenPGP ECC Curve-specific Wire Formats containing <xref target="ecc-wire-f
ormats-registry"/>.</t>
<t>OpenPGP Hash Algorithm Identifiers for RSA Signatures use of EMSA-PKCS1-v1_
5 Padding containing <xref target="emsa-hash-oids-registry"/>.</t>
<t>OpenPGP AEAD Algorithms containing <xref target="aead-algorithms-registry"/
>.</t>
<t>OpenPGP Encrypted Message Packet Versions containing <xref target="encrypte
d-packet-versions-registry"/>.</t>
<t>OpenPGP Key and Signature Versions containing <xref target="signed-packet-v
ersions-registry"/>.</t>
<t>OpenPGP Elliptic Curve Point Wire Formats containing <xref target="ec-point
-wire-formats-registry"/>.</t>
<t>OpenPGP Elliptic Curve Scalar Encodings containing <xref target="ec-scalar-
wire-formats-registry"/>.</t>
<t>OpenPGP ECDH KDF and KEK Parameters containing <xref target="ecdh-kdf-kek-p
arameters-registry"/>.</t>
</list></t>
</section> <!-- tab 13 ok -->
<section anchor="registration-policies"><name>Registration Policies</name> <t>IANA has renamed the "PGP User Attribute Types" registry to "OpenPGP
User Attribute Subpacket Types" and updated its contents as shown in <xref targe
t="user-attr-subpacket-types-registry"/>.</t>
<t>IANA is requested to set all registries within the OpenPGP protocol group to <!-- tab 15 ok -->
use the SPECIFICATION <bcp14>REQUIRED</bcp14> registration policy, see <xref sec <t>IANA has renamed the "Image Format Subpacket Types" registry to "Open
tion="4.6" sectionFormat="of" target="RFC8126"/> with the exception of the regis PGP Image Attribute Encoding Format" and updated its contents as shown in <xref
tries listed in <xref target="rfc-required-registries"/>, below. target="image-attr-encoding-format-registry"/>.</t>
This policy means that review and approval by a designated expert is required, a
nd that the IDs and their meanings must be documented in a permanent and readily
available public specification, in sufficient detail so that interoperability b
etween independent implementations is possible.</t>
<section anchor="rfc-required-registries"><name>Registries that are RFC REQUIRED <!-- tab 18 ok -->
</name> <t>IANA has renamed the "Public Key Algorithms" registry to "OpenPGP Pub
lic Key Algorithms" and updated its contents as shown in <xref target="pubkey-al
go-registry"/>.</t>
<t>The following registries use the RFC <bcp14>REQUIRED</bcp14> registration pol <!-- tab 21 ok -->
icy, as described in <xref section="4.7" sectionFormat="of" target="RFC8126"/>:< <t>IANA has renamed the "Symmetric Key Algorithms" registry to "OpenPGP
/t> Symmetric Key Algorithms" and updated its contents as shown in <xref target="sym
key-algorithms-registry"/>.</t>
<t><list style="symbols"> <!-- tab 22 ok -->
<t>OpenPGP Packet Types registry (<xref target="packet-types-registry"/>)</t> <t>IANA has renamed the "Compression Algorithms" registry to "OpenPGP Co
<t>OpenPGP Key and Signature Versions registry (<xref target="signed-packet-ve mpression Algorithms" and updated its contents as shown in <xref target="compres
rsions-registry"/>)</t> sion-algorithms-registry"/>.</t>
<t>OpenPGP Key ID and Fingerprint registry (<xref target="key-id-fingerprint-r
egistry"/>)</t>
<t>OpenPGP Encrypted Message Packet Versions registry (<xref target="encrypted
-packet-versions-registry"/>)</t>
</list></t>
</section> <!-- tab 23 ok -->
</section> <t>IANA has renamed the "Hash Algorithms" registry to "OpenPGP Hash Algo
<section anchor="designated-experts"><name>Designated Experts</name> rithms" and updated its contents as shown in <xref target="hash-algorithms-regis
try"/>.</t>
<t>The designated experts will determine whether the new registrations retain th </section>
e security properties that are expected by the base implementation and that thes <section anchor="removed-registries">
e new registrations do not cause interoperability issues with existing implement <name>Removed Registry</name>
ations other than not producing or consuming the IDs associated with these new r <t>IANA has marked the empty "New Packet Versions" registry as OBSOLETE.
egistrations. </t>
Registration proposals that fail to meet these criteria could instead be propose <t>A tombstone note has been added to the OpenPGP protocol group with th
d as new work items for the OpenPGP working group or its successor.</t> e following content:</t>
<t>The subsections below describe specific guidance for classes of registry upda <blockquote>Those wishing to use the removed "New Packet Versions" registry shou
tes that a designated expert will consider.</t> ld instead register new versions of the relevant packets in the "OpenPGP Key and
Signature Versions", "OpenPGP Key IDs and Fingerprints", and "OpenPGP Encrypted
Message Packet Versions" registries.</blockquote>
</section>
<section anchor="added-registries">
<name>Added Registries</name>
<t>IANA has added the following registries in the OpenPGP protocol group
. Note that the initial contents of each registry is shown in the corresponding
table.</t>
<ul spacing="normal">
<li>
<!-- tab 2 ok -->
<t>"OpenPGP Secret Key Encryption (S2K Usage Octet)" (<xref target="
secret-key-protection-registry"/>).</t>
</li>
<t>The designated experts should also consider <xref target="meta-considerations <!-- tab 4 ok -->
-for-expansion"/> when reviewing proposed additions to the OpenPGP registries.</ <li>
t> <t>"OpenPGP Signature Types" (<xref target="signature-types-registry
"/>).</t>
</li>
<section anchor="key-and-signature-versions"><name>Key and Signature Versions</n <!-- tab 6 ok -->
ame> <li>
<t>"OpenPGP Signature Notation Data Subpacket Notation Flags" (<xref
target="sig-note-data-note-flags-registry"/>).</t>
</li>
<t>When defining a new version of OpenPGP keys or signatures, <xref target="sign <!-- tab 7 ok -->
ed-packet-versions-registry"/> should be updated, <li>
When a new version of OpenPGP key is defined, <xref target="key-id-fingerprint-r <t>"OpenPGP Signature Notation Data Subpacket Types" (<xref target="
egistry"/> should also be updated.</t> sig-note-data-subpacket-types"/>).</t>
</li>
</section> <!-- tab 12 ok - made this plural -->
<section anchor="encryption-versions"><name>Encryption Versions</name> <li>
<t>"OpenPGP Key IDs and Fingerprints" (<xref target="key-id-fingerpr
int-registry"/>).</t>
</li>
<t>When defining a new version of the Symmetrically Encrypted Integrity Protecte <!-- tab 14 ok - made this plural -->
d Data Packet (<xref target="seipd"/>), Public Key Encrypted Session Key Packet <li>
(<xref target="pkesk"/>), and/or Symmetric Key Encrypted Session Key Packet (<xr <t>"OpenPGP Image Attribute Versions" (<xref target="image-attribute
ef target="skesk"/>), the registry from <xref target="encrypted-packet-versions- -version-registry"/>).</t>
registry"/> needs to be updated. </li>
When the SEIPD is updated, consider also adding a corresponding flag to <xref ta
rget="features-flags-registry"/>.</t>
</section> <!-- tab 16 ok - made this plural -->
<section anchor="algorithms"><name>Algorithms</name> <li>
<t>"OpenPGP Armor Header Lines" (<xref target="armor-header-line-reg
istry"/>).</t>
</li>
<t><xref target="constants"/> lists the cryptographic and compression algorithms <!-- tab 17 ok - made this plural -->
that OpenPGP uses. <li>
Adding new algorithms is usually simple, in some cases as little as allocating a <t>"OpenPGP Armor Header Keys" (<xref target="armor-header-key-regis
n ID and pointing to a reference. try"/>).</t>
But some algorithm registries require some subtle additional details when a new </li>
algorithm is introduced.</t>
<section anchor="elliptic-curve-algorithms"><name>Elliptic Curve Algorithms</nam <!-- tab 19 ok - made this plural -->
e> <li>
<t>"OpenPGP ECC Curve OIDs and Usage" (<xref target="ecc-oid-usage-r
egistry"/>).</t>
</li>
<t>To register a new elliptic curve for use with OpenPGP, its OID needs to be re <!-- tab 20 ok -->
gistered in <xref target="ecc-oid-usage-registry"/>, its wire format needs to be <li>
documented in <xref target="ecc-wire-formats-registry"/>, and if used for ECDH, <t>"OpenPGP ECC Curve-Specific Wire Formats" (<xref target="ecc-wire
its KDF and KEK parameters must be populated in <xref target="ecdh-kdf-kek-para -formats-registry"/>).</t>
meters-registry"/>. </li>
If the wire format(s) used are not already defined in <xref target="ec-point-wir
e-formats-registry"/> or <xref target="ec-scalar-wire-formats-registry"/>, they
should be defined there as well.</t>
</section> <!-- tab 24 ok - added apostrophe and capped "use" -->
<section anchor="symmetric-key-algorithms"><name>Symmetric-Key Algorithms</name> <li>
<t>"OpenPGP Hash Algorithm Identifiers for RSA Signatures' Use of EM
SA-PKCS1-v1_5 Padding" (<xref target="emsa-hash-oids-registry"/>).</t>
</li>
<t>When registering a new symmetric cipher with a block size of 64 or 128 bits a <!-- tab 25 ok -->
nd a key size that is a multiple of 64 bits, no new considerations are needed.</ <li>
t> <t>"OpenPGP AEAD Algorithms" (<xref target="aead-algorithms-registry
"/>).</t>
</li>
<t>If the new cipher has a different block size, there needs to be additional do <!-- tab 26 ok -->
cumentation describing how to use the cipher in CFB mode.</t> <li>
<t>"OpenPGP Encrypted Message Packet Versions" (<xref target="encryp
ted-packet-versions-registry"/>).</t>
</li>
<t>If the new cipher has an unusual key size, then padding needs to be considere <!-- tab 27 ok -->
d for X25519 and X448 keywrap, which currently needs no padding.</t> <li>
<t>"OpenPGP Key and Signature Versions" (<xref target="signed-packet
-versions-registry"/>).</t>
</li>
</section> <!-- tab 28 ok -->
<section anchor="hash-algorithms"><name>Hash Algorithms</name> <li>
<t>"OpenPGP Elliptic Curve Point Wire Formats" (<xref target="ec-poi
nt-wire-formats-registry"/>).</t>
</li>
<t>When registering a new hash algorithm (in <xref target="hash-algorithms-regis <!-- tab 29 ok -->
try"/>), if the algorithm is also to be used with RSA signing schemes, it must a <li>
lso have an entry in <xref target="emsa-hash-oids-registry"/>.</t> <t>"OpenPGP Elliptic Curve Scalar Encodings" (<xref target="ec-scala
r-wire-formats-registry"/>).</t>
</li>
</section> <!-- tab 30 ok -->
</section> <li>
</section> <t>"OpenPGP ECDH KDF and KEK Parameters" (<xref target="ecdh-kdf-kek
</section> -parameters-registry"/>).</t>
</li>
</ul>
</section>
<section anchor="registration-policies">
<name>Registration Policies</name>
<t>All registries within the OpenPGP protocol group, with the exception
of the registries listed in <xref target="rfc-required-registries"/>, use the Sp
ecification Required registration policy; see <xref section="4.6" sectionFormat=
"of" target="RFC8126"/>.
This policy means that review and approval by a designated expert is required an
d that the IDs and their meanings must be documented in a permanent and readily
available public specification, in sufficient detail, so that interoperability b
etween independent implementations is possible.</t>
<section anchor="rfc-required-registries">
<name>Registries That Use RFC Required</name>
<t>The following registries use the RFC Required registration policy,
as described in <xref section="4.7" sectionFormat="of" target="RFC8126"/>:</t>
<ul spacing="normal">
<!-- tab 3 ok -->
<li>
<t>"OpenPGP Packet Types" (<xref target="packet-types-registry"/>)
.</t>
</li>
<!-- tab 12 ok -->
<li>
<t>"OpenPGP Key IDs and Fingerprints" (<xref target="key-id-finger
print-registry"/>).</t>
</li>
<!-- tab 26 ok -->
<li>
<t>"OpenPGP Encrypted Message Packet Versions" (<xref target="encr
ypted-packet-versions-registry"/>).</t>
</li>
<!-- tab 27 ok -->
<li>
<t>"OpenPGP Key and Signature Versions" (<xref target="signed-pack
et-versions-registry"/>).</t>
</li>
</ul>
</section>
</section>
<section anchor="designated-experts">
<name>Designated Experts</name>
<t>The designated experts will determine whether the new registrations r
etain the security properties that are expected by the base implementation and w
hether these new registrations do not cause interoperability issues with existin
g implementations, other than not producing or consuming the IDs associated with
these new registrations.
Registration proposals that fail to meet these criteria could instead be propose
d as new work items for the OpenPGP Working Group or its successor.</t>
<t>The subsections below describe specific guidance for classes of regis
try updates that a designated expert will consider.</t>
<t>The designated experts should also consider <xref target="meta-consid
erations-for-expansion"/> when reviewing proposed additions to the OpenPGP proto
col group.</t>
<section anchor="key-and-signature-versions">
<name>Key and Signature Versions</name>
<t>When defining a new version of OpenPGP Keys or Signatures, the "Ope
nPGP Key and Signature Versions" registry (<xref target="signed-packet-versions-
registry"/>) should be updated. When a new version of OpenPGP Key is defined, th
e "OpenPGP Key IDs and Fingerprints" registry (<xref target="key-id-fingerprint-
registry"/>) should also be updated.</t>
</section>
<section anchor="encryption-versions">
<name>Encryption Versions</name>
<t>When defining a new version of the Symmetrically Encrypted and Inte
grity Protected Data packet (<xref target="seipd"/>), Public Key Encrypted Sessi
on Key packet (<xref target="pkesk"/>), and/or Symmetric Key Encrypted Session K
ey packet (<xref target="skesk"/>), the "OpenPGP Encrypted Message Packet Versio
ns" registry (<xref target="encrypted-packet-versions-registry"/>) should be upd
ated. When the SEIPD is updated, consider also adding a corresponding flag to th
e "OpenPGP Features Flags" registry (<xref target="features-flags-registry"/>).<
/t>
</section>
<section anchor="algorithms">
<name>Algorithms</name>
<t><xref target="constants"/> lists the cryptographic and compression
algorithms that OpenPGP uses.
Adding new algorithms is usually simple; in some cases, allocating an ID and poi
nting to a reference is only needed. But some algorithm registries require some
subtle additional details when a new algorithm is introduced.</t>
<section anchor="elliptic-curve-algorithms">
<name>Elliptic Curve Algorithms</name>
<t>To register a new elliptic curve for use with OpenPGP, its OID ne
eds to be registered in the "OpenPGP ECC Curve OIDs and Usage" registry (<xref t
arget="ecc-oid-usage-registry"/>), its wire format needs to be documented in the
"OpenPGP ECC Curve-Specific Wire Formats" registry (<xref target="ecc-wire-form
ats-registry"/>), and if used for ECDH, its KDF and KEK parameters must be popul
ated in the "OpenPGP ECDH KDF and KEK Parameters" registry (<xref target="ecdh-k
df-kek-parameters-registry"/>). If the wire format(s) used is not already define
d in the "OpenPGP Elliptic Curve Point Wire Formats" (<xref target="ec-point-wir
e-formats-registry"/>) or "OpenPGP Elliptic Curve Scalar Encodings" (<xref targe
t="ec-scalar-wire-formats-registry"/>) registries, they should be defined there
as well.</t>
</section>
<section anchor="symmetric-key-algorithms">
<name>Symmetric Key Algorithms</name>
<t>When registering a new symmetric cipher with a block size of 64 o
r 128 bits and a key size that is a multiple of 64 bits, no new considerations a
re needed.</t>
<t>If the new cipher has a different block size, there needs to be a
dditional documentation describing how to use the cipher in CFB mode.</t>
<t>If the new cipher has an unusual key size, then padding needs to
be considered for X25519 and X448 key wrapping, which currently needs no padding
.</t>
</section>
<section anchor="hash-algorithms">
<name>Hash Algorithms</name>
<t>When registering a new hash algorithm in the "OpenPGP Hash Algori
thms" registry (<xref target="hash-algorithms-registry"/>), if the algorithm is
also to be used with RSA signing schemes, it must also have an entry in the "Ope
nPGP Hash Algorithm Identifiers for RSA Signatures' Use of EMSA-PKCS1-v1_5 Paddi
ng" registry (<xref target="emsa-hash-oids-registry"/>).</t>
</section>
</section>
</section>
</section>
</middle> </middle>
<back> <back>
<references title='Normative References'> <references>
<name>References</name>
<reference anchor="BLOWFISH" target="http://www.counterpane.com/bfsverlag.html"> <references>
<front> <name>Normative References</name>
<title>Description of a New Variable-Length Key, 64-Bit Block Cipher (Blowfi
sh)</title>
<author initials="B." surname="Schneier">
<organization></organization>
</author>
<date year="1993" month="December"/>
</front>
<seriesInfo name="Fast Software Encryption, Cambridge Security Workshop Procee
dings" value="Springer-Verlag, 1994, pp191-204"/>
</reference>
<reference anchor="BZ2" target="http://www.bzip.org/">
<front>
<title>The Bzip2 and libbzip2 home page</title>
<author initials="J." surname="Seward" fullname="Julian Seward, jseward@acm.
org">
<organization></organization>
</author>
<date year="2010"/>
</front>
</reference>
<reference anchor="EAX" target="https://seclab.cs.ucdavis.edu/papers/eax.pdf">
<front>
<title>A Conventional Authenticated-Encryption Mode</title>
<author initials="M." surname="Bellare">
<organization></organization>
</author>
<author initials="P." surname="Rogaway">
<organization></organization>
</author>
<author initials="D." surname="Wagner">
<organization></organization>
</author>
<date year="2003" month="April"/>
</front>
</reference>
<reference anchor="ELGAMAL" >
<front>
<title>A Public-Key Cryptosystem and a Signature Scheme Based on Discrete Lo
garithms</title>
<author initials="T." surname="Elgamal">
<organization></organization>
</author>
<date year="1985"/>
</front>
<seriesInfo name="IEEE Transactions on Information Theory" value="v. IT-31, n.
4, 1985, pp. 469-472"/>
</reference>
<reference anchor="IDEA" >
<front>
<title>On the design and security of block ciphers</title>
<author initials="X." surname="Lai">
<organization></organization>
</author>
<date year="1992"/>
</front>
<seriesInfo name="ETH Series in Information Processing, J.L. Massey (editor)"
value="Vol. 1, Hartung-Gorre Verlag Konstanz, Technische Hochschule (Zurich)"/>
</reference>
<reference anchor="ISO10646" target="https://www.iso.org/standard/76835.html">
<front>
<title>Information Technology - Universal Multiple-octet coded Character Set
(UCS) - Part 1: Architecture and Basic Multilingual Plane</title>
<author >
<organization>International Organization for Standardization</organization
>
</author>
<date year="2020"/>
</front>
<seriesInfo name="ISO" value="Standard 10646-1"/>
</reference>
<reference anchor="JFIF" target="https://www.itu.int/rec/T-REC-T.871-201105-I">
<front>
<title>Information technology – Digital compression and coding of continuous
-tone still images: JPEG File Interchange Format (JFIF)</title>
<author >
<organization>International Telecommunication Union</organization>
</author>
<date year="2011" month="May" day="14"/>
</front>
<seriesInfo name="ISO" value="ISO/IEC 10918-5"/>
</reference>
<reference anchor='RFC1321'>
<front>
<title>The MD5 Message-Digest Algorithm</title>
<author fullname='R. Rivest' initials='R.' surname='Rivest'/>
<date month='April' year='1992'/>
<abstract>
<t>This document describes the MD5 message-digest algorithm. The algorithm
takes as input a message of arbitrary length and produces as output a 128-bit "
fingerprint" or "message digest" of the input. This memo provides information fo
r the Internet community. It does not specify an Internet standard.</t>
</abstract>
</front>
<seriesInfo name='RFC' value='1321'/>
<seriesInfo name='DOI' value='10.17487/RFC1321'/>
</reference>
<reference anchor='RFC1950'> <reference anchor="BLOWFISH" target="https://www.schneier.com/academic/a
<front> rchives/1994/09/description_of_a_new.html">
<title>ZLIB Compressed Data Format Specification version 3.3</title> <front>
<author fullname='P. Deutsch' initials='P.' surname='Deutsch'/> <title>Description of a New Variable-Length Key, 64-Bit Block Cipher
<author fullname='J-L. Gailly' surname='J-L. Gailly'/> (Blowfish)</title>
<date month='May' year='1996'/> <author initials="B." surname="Schneier">
<abstract> <organization/>
<t>This specification defines a lossless compressed data format. This memo </author>
provides information for the Internet community. This memo does not specify an <date year="1993" month="December"/>
Internet standard of any kind.</t> </front>
</abstract> <refcontent>Fast Software Encryption, Cambridge Security Workshop Proce
</front> edings, pp. 191-204</refcontent>
<seriesInfo name='RFC' value='1950'/> </reference>
<seriesInfo name='DOI' value='10.17487/RFC1950'/> <reference anchor="BZ2" target="https://sourceware.org/bzip2/">
</reference> <front>
<title>bzip2 and libbzip2</title>
<author>
<organization>bzip2</organization>
</author>
<date year="2010"/>
</front>
</reference>
<reference anchor='RFC1951'> <reference anchor="EAX" target="https://seclab.cs.ucdavis.edu/papers/eax
<front> .pdf">
<title>DEFLATE Compressed Data Format Specification version 1.3</title> <front>
<author fullname='P. Deutsch' initials='P.' surname='Deutsch'/> <title>A Conventional Authenticated-Encryption Mode</title>
<date month='May' year='1996'/> <author initials="M." surname="Bellare">
<abstract> <organization/>
<t>This specification defines a lossless compressed data format that compr </author>
esses data using a combination of the LZ77 algorithm and Huffman coding, with ef <author initials="P." surname="Rogaway">
ficiency comparable to the best currently available general-purpose compression <organization/>
methods. This memo provides information for the Internet community. This memo do </author>
es not specify an Internet standard of any kind.</t> <author initials="D." surname="Wagner">
</abstract> <organization/>
</front> </author>
<seriesInfo name='RFC' value='1951'/> <date year="2003" month="April"/>
<seriesInfo name='DOI' value='10.17487/RFC1951'/> </front>
</reference> </reference>
<reference anchor='RFC2144'> <reference anchor="ELGAMAL">
<front> <front>
<title>The CAST-128 Encryption Algorithm</title> <title>A Public Key Cryptosystem and a Signature Scheme Based on Dis
<author fullname='C. Adams' initials='C.' surname='Adams'/> crete Logarithms</title>
<date month='May' year='1997'/> <author initials="T." surname="Elgamal">
<abstract> <organization/>
<t>There is a need in the Internet community for an unencumbered encryptio </author>
n algorithm with a range of key sizes that can provide security for a variety of <date month="July" year="1985"/>
cryptographic applications and protocols. This document describes an existing a </front>
lgorithm that can be used to satisfy this requirement. This memo provides inform <seriesInfo name="DOI" value="10.1109/TIT.1985.1057074"/>
ation for the Internet community. This memo does not specify an Internet standar <refcontent>IEEE Transactions on Information Theory, Vol. 31, Issue 4,
d of any kind.</t> pp. 469-472</refcontent>
</abstract> </reference>
</front>
<seriesInfo name='RFC' value='2144'/>
<seriesInfo name='DOI' value='10.17487/RFC2144'/>
</reference>
<reference anchor='RFC2822'> <reference anchor="IDEA" target="https://link.springer.com/chapter/10.10
<front> 07/3-540-46877-3_35">
<title>Internet Message Format</title> <front>
<author fullname='P. Resnick' initials='P.' role='editor' surname='Resnick'/ <title>A Proposal for a New Block Encryption Standard</title>
> <author initials="X." surname="Lai">
<date month='April' year='2001'/> <organization/>
<abstract> </author>
<t>This document specifies a syntax for text messages that are sent betwee <author initials="J. L." surname="Massey">
n computer users, within the framework of "electronic mail" messages. [STANDARDS <organization/>
-TRACK]</t> </author>
</abstract> <date month="January" year="1991"/>
</front> </front>
<seriesInfo name='RFC' value='2822'/> <refcontent>Advances in Cryptology - EUROCRYPT '90, Vol. 473, pp. 389-
<seriesInfo name='DOI' value='10.17487/RFC2822'/> 404</refcontent>
</reference> <seriesInfo name="DOI" value="10.1007/3-540-46877-3_35"/>
</reference>
<reference anchor='RFC2898'> <reference anchor="ISO10646" target="https://www.iso.org/standard/76835.
<front> html">
<title>PKCS #5: Password-Based Cryptography Specification Version 2.0</title <front>
> <title>Information technology - Universal coded character set (UCS)<
<author fullname='B. Kaliski' initials='B.' surname='Kaliski'/> /title>
<date month='September' year='2000'/> <author>
<abstract> <organization>ISO</organization>
<t>This document provides recommendations for the implementation of passwo </author>
rd-based cryptography, covering key derivation functions, encryption schemes, me <date month="December" year="2020"/>
ssage-authentication schemes, and ASN.1 syntax identifying the techniques. This </front>
memo provides information for the Internet community.</t> <seriesInfo name="ISO/IEC" value="10646:2020"/>
</abstract> </reference>
</front>
<seriesInfo name='RFC' value='2898'/>
<seriesInfo name='DOI' value='10.17487/RFC2898'/>
</reference>
<reference anchor='RFC3156'> <reference anchor="JFIF" target="https://www.itu.int/rec/T-REC-T.871-201
<front> 105-I">
<title>MIME Security with OpenPGP</title> <front>
<author fullname='M. Elkins' initials='M.' surname='Elkins'/> <title>Information technology - Digital compression and coding of co
<author fullname='D. Del Torto' initials='D.' surname='Del Torto'/> ntinuous-tone still images: JPEG File Interchange Format (JFIF)</title>
<author fullname='R. Levien' initials='R.' surname='Levien'/> <author>
<author fullname='T. Roessler' initials='T.' surname='Roessler'/> <organization>ITU-T</organization>
<date month='August' year='2001'/> </author>
<abstract> <date year="2011" month="May"/>
<t>This document describes how the OpenPGP Message Format can be used to p </front>
rovide privacy and authentication using the Multipurpose Internet Mail Extension <seriesInfo name="Recommendation" value="ITU-T T.871"/>
s (MIME) security content types described in RFC 1847. [STANDARDS-TRACK]</t> </reference>
</abstract>
</front>
<seriesInfo name='RFC' value='3156'/>
<seriesInfo name='DOI' value='10.17487/RFC3156'/>
</reference>
<reference anchor='RFC3394'> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1
<front> 321.xml"/>
<title>Advanced Encryption Standard (AES) Key Wrap Algorithm</title> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1
<author fullname='J. Schaad' initials='J.' surname='Schaad'/> 950.xml"/>
<author fullname='R. Housley' initials='R.' surname='Housley'/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1
<date month='September' year='2002'/> 951.xml"/>
</front> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
<seriesInfo name='RFC' value='3394'/> 144.xml"/>
<seriesInfo name='DOI' value='10.17487/RFC3394'/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.28
</reference> 22.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
156.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
394.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
629.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
713.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
086.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
648.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
322.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
234.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
253.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
748.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
017.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.80
18.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
032.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
126.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
106.xml"/>
<reference anchor='RFC3629'> <reference anchor="RIPEMD-160">
<front> <front>
<title>UTF-8, a transformation format of ISO 10646</title> <title>Information technology - Security techniques - Hash-functions
<author fullname='F. Yergeau' initials='F.' surname='Yergeau'/> - Part 3: Dedicated hash-functions</title>
<date month='November' year='2003'/> <author>
<abstract> <organization>ISO</organization>
<t>ISO/IEC 10646-1 defines a large character set called the Universal Char </author>
acter Set (UCS) which encompasses most of the world's writing systems. The origi <date month="May" year="1998"/>
nally proposed encodings of the UCS, however, were not compatible with many curr </front>
ent applications and protocols, and this has led to the development of UTF-8, th <seriesInfo name="ISO/IEC" value="10118-3:1998"/>
e object of this memo. UTF-8 has the characteristic of preserving the full US-AS </reference>
CII range, providing compatibility with file systems, parsers and other software
that rely on US-ASCII values but are transparent to other values. This memo obs
oletes and replaces RFC 2279.</t>
</abstract>
</front>
<seriesInfo name='STD' value='63'/>
<seriesInfo name='RFC' value='3629'/>
<seriesInfo name='DOI' value='10.17487/RFC3629'/>
</reference>
<reference anchor='RFC3713'> <reference anchor="SP800-38A" target="https://nvlpubs.nist.gov/nistpubs/
<front> legacy/sp/nistspecialpublication800-38a.pdf">
<title>A Description of the Camellia Encryption Algorithm</title> <front>
<author fullname='M. Matsui' initials='M.' surname='Matsui'/> <title>Recommendation for Block Cipher Modes of Operation: Methods a
<author fullname='J. Nakajima' initials='J.' surname='Nakajima'/> nd Techniques</title>
<author fullname='S. Moriai' initials='S.' surname='Moriai'/> <author>
<date month='April' year='2004'/> <organization>NIST</organization>
<abstract> </author>
<t>This document describes the Camellia encryption algorithm. Camellia is <date year="2001" month="December"/>
a block cipher with 128-bit block size and 128-, 192-, and 256-bit keys. The alg </front>
orithm description is presented together with key scheduling part and data rando <seriesInfo name="NIST Special Publication" value="800-38A"/>
mizing part. This memo provides information for the Internet community.</t> <seriesInfo name="DOI" value="10.6028/NIST.SP.800-38A"/>
</abstract> </reference>
</front>
<seriesInfo name='RFC' value='3713'/>
<seriesInfo name='DOI' value='10.17487/RFC3713'/>
</reference>
<reference anchor='RFC4086'> <reference anchor="SP800-38D" target="https://nvlpubs.nist.gov/nistpubs
<front> /legacy/sp/nistspecialpublication800-38d.pdf">
<title>Randomness Requirements for Security</title> <front>
<author fullname='D. Eastlake 3rd' initials='D.' surname='Eastlake 3rd'/> <title>Recommendation for Block Cipher Modes of Operation: Galois/Co
<author fullname='J. Schiller' initials='J.' surname='Schiller'/> unter Mode (GCM) and GMAC</title>
<author fullname='S. Crocker' initials='S.' surname='Crocker'/> <author>
<date month='June' year='2005'/> <organization>NIST</organization>
<abstract> </author>
<t>Security systems are built on strong cryptographic algorithms that foil <date year="2007" month="November"/>
pattern analysis attempts. However, the security of these systems is dependent </front>
on generating secret quantities for passwords, cryptographic keys, and similar q <seriesInfo name="NIST Special Publication" value="800-38D"/>
uantities. The use of pseudo-random processes to generate secret quantities can <seriesInfo name="DOI" value="10.6028/NIST.SP.800-38D"/>
result in pseudo-security. A sophisticated attacker may find it easier to reprod </reference>
uce the environment that produced the secret quantities and to search the result
ing small set of possibilities than to locate the quantities in the whole of the
potential number space.</t>
<t>Choosing random quantities to foil a resourceful and motivated adversar
y is surprisingly difficult. This document points out many pitfalls in using poo
r entropy sources or traditional pseudo-random number generation techniques for
generating such quantities. It recommends the use of truly random hardware techn
iques and shows that the existing hardware on many systems can be used for this
purpose. It provides suggestions to ameliorate the problem when a hardware solut
ion is not available, and it gives examples of how large such quantities need to
be for some applications. This document specifies an Internet Best Current Prac
tices for the Internet Community, and requests discussion and suggestions for im
provements.</t>
</abstract>
</front>
<seriesInfo name='BCP' value='106'/>
<seriesInfo name='RFC' value='4086'/>
<seriesInfo name='DOI' value='10.17487/RFC4086'/>
</reference>
<reference anchor='RFC4648'> <reference anchor="SP800-56A" target="https://nvlpubs.nist.gov/nistpubs/
<front> SpecialPublications/
<title>The Base16, Base32, and Base64 Data Encodings</title> nist.sp.800-56Ar3.pdf">
<author fullname='S. Josefsson' initials='S.' surname='Josefsson'/> <front>
<date month='October' year='2006'/> <title>Recommendation for Pair-Wise Key Establishment Schemes Using
<abstract> Discrete Logarithm Cryptography</title>
<t>This document describes the commonly used base 64, base 32, and base 16 <author>
encoding schemes. It also discusses the use of line-feeds in encoded data, use <organization>NIST</organization>
of padding in encoded data, use of non-alphabet characters in encoded data, use </author>
of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK]</t> <date year="2018" month="April"/>
</abstract> </front>
</front> <seriesInfo name="NIST Special Publication" value="800-56A Revision 3"
<seriesInfo name='RFC' value='4648'/> />
<seriesInfo name='DOI' value='10.17487/RFC4648'/> <seriesInfo name="DOI" value="10.6028/NIST.SP.800-56Ar"/>
</reference> </reference>
<reference anchor='RFC5322'> <reference anchor="SP800-67" target="https://nvlpubs.nist.gov/nistpubs/S
<front> pecialPublications/NIST.SP.800-67r2.pdf">
<title>Internet Message Format</title> <front>
<author fullname='P. Resnick' initials='P.' role='editor' surname='Resnick'/ <title>Recommendation for the Triple Data Encryption Algorithm (TDEA
> ) Block Cipher</title>
<date month='October' year='2008'/> <author>
<abstract> <organization>NIST</organization>
<t>This document specifies the Internet Message Format (IMF), a syntax for </author>
text messages that are sent between computer users, within the framework of "el <date year="2017" month="November"/>
ectronic mail" messages. This specification is a revision of Request For Comment </front>
s (RFC) 2822, which itself superseded Request For Comments (RFC) 822, "Standard <seriesInfo name="NIST Special Publication" value="800-67 Revision 2"/
for the Format of ARPA Internet Text Messages", updating it to reflect current p >
ractice and incorporating incremental changes that were specified in other RFCs. <seriesInfo name="DOI" value="10.6028/NIST.SP.800-67r2"/>
[STANDARDS-TRACK]</t> </reference>
</abstract>
</front>
<seriesInfo name='RFC' value='5322'/>
<seriesInfo name='DOI' value='10.17487/RFC5322'/>
</reference>
<reference anchor='RFC6234'> <reference anchor="TWOFISH" target="https://www.schneier.com/wp-content/
<front> uploads/2016/02/paper-twofish-paper.pdf">
<title>US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)</title> <front>
<author fullname='D. Eastlake 3rd' initials='D.' surname='Eastlake 3rd'/> <title>Twofish: A 128-Bit Block Cipher</title>
<author fullname='T. Hansen' initials='T.' surname='Hansen'/> <author initials="B." surname="Schneier">
<date month='May' year='2011'/> <organization/>
<abstract> </author>
<t>Federal Information Processing Standard, FIPS</t> <author initials="J." surname="Kelsey">
</abstract> <organization/>
</front> </author>
<seriesInfo name='RFC' value='6234'/> <author initials="D." surname="Whiting">
<seriesInfo name='DOI' value='10.17487/RFC6234'/> <organization/>
</reference> </author>
<author initials="D." surname="Wagner">
<organization/>
</author>
<author initials="C." surname="Hall">
<organization/>
</author>
<author initials="N." surname="Ferguson">
<organization/>
</author>
<date month="June" year="1998"/>
</front>
</reference>
<reference anchor='RFC7253'> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
<front> 119.xml"/>
<title>The OCB Authenticated-Encryption Algorithm</title> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
<author fullname='T. Krovetz' initials='T.' surname='Krovetz'/> 174.xml"/>
<author fullname='P. Rogaway' initials='P.' surname='Rogaway'/>
<date month='May' year='2014'/>
<abstract>
<t>This document specifies OCB, a shared-key blockcipher-based encryption
scheme that provides confidentiality and authenticity for plaintexts and authent
icity for associated data. This document is a product of the Crypto Forum Resear
ch Group (CFRG).</t>
</abstract>
</front>
<seriesInfo name='RFC' value='7253'/>
<seriesInfo name='DOI' value='10.17487/RFC7253'/>
</reference>
<reference anchor='RFC7748'> <reference anchor="FIPS186" target="https://nvlpubs.nist.gov/nistpubs/FI
<front> PS/NIST.FIPS.186-5.pdf">
<title>Elliptic Curves for Security</title> <front>
<author fullname='A. Langley' initials='A.' surname='Langley'/> <title>Digital Signature Standard (DSS)</title>
<author fullname='M. Hamburg' initials='M.' surname='Hamburg'/> <author>
<author fullname='S. Turner' initials='S.' surname='Turner'/> <organization>NIST</organization>
<date month='January' year='2016'/> </author>
<abstract> <date month="February" year="2023"/>
<t>This memo specifies two elliptic curves over prime fields that offer a </front>
high level of practical security in cryptographic applications, including Transp <seriesInfo name="FIPS PUB" value="186-5"/>
ort Layer Security (TLS). These curves are intended to operate at the ~128-bit a <seriesInfo name="DOI" value="10.6028/NIST.FIPS.186-5"/>
nd ~224-bit security level, respectively, and are generated deterministically ba </reference>
sed on a list of required properties.</t>
</abstract>
</front>
<seriesInfo name='RFC' value='7748'/>
<seriesInfo name='DOI' value='10.17487/RFC7748'/>
</reference>
<reference anchor='RFC8017'> <reference anchor="AES" target="https://nvlpubs.nist.gov/nistpubs/FIPS/N
<front> IST.FIPS.197-upd1.pdf">
<title>PKCS #1: RSA Cryptography Specifications Version 2.2</title> <front>
<author fullname='K. Moriarty' initials='K.' role='editor' surname='Moriarty <title>Advanced Encryption Standard (AES)</title>
'/> <author>
<author fullname='B. Kaliski' initials='B.' surname='Kaliski'/> <organization>NIST</organization>
<author fullname='J. Jonsson' initials='J.' surname='Jonsson'/> </author>
<author fullname='A. Rusch' initials='A.' surname='Rusch'/> <date month="November" year="2001"/>
<date month='November' year='2016'/> </front>
<abstract> <seriesInfo name="FIPS PUB" value="197"/>
<t>This document provides recommendations for the implementation of public <seriesInfo name="DOI" value="10.6028/NIST.FIPS.197-upd1"/>
-key cryptography based on the RSA algorithm, covering cryptographic primitives, <refcontent>Updated May 2023</refcontent>
encryption schemes, signature schemes with appendix, and ASN.1 syntax for repre </reference>
senting keys and for identifying the schemes.</t>
<t>This document represents a republication of PKCS #1 v2.2 from RSA Labor
atories' Public-Key Cryptography Standards (PKCS) series. By publishing this RFC
, change control is transferred to the IETF.</t>
<t>This document also obsoletes RFC 3447.</t>
</abstract>
</front>
<seriesInfo name='RFC' value='8017'/>
<seriesInfo name='DOI' value='10.17487/RFC8017'/>
</reference>
<reference anchor='RFC8032'> <reference anchor="FIPS180" target="https://nvlpubs.nist.gov/nistpubs/fi
<front> ps/nist.fips.180-4.pdf">
<title>Edwards-Curve Digital Signature Algorithm (EdDSA)</title> <front>
<author fullname='S. Josefsson' initials='S.' surname='Josefsson'/> <title>Secure Hash Standard (SHS)</title>
<author fullname='I. Liusvaara' initials='I.' surname='Liusvaara'/> <author>
<date month='January' year='2017'/> <organization>NIST</organization>
<abstract> </author>
<t>This document describes elliptic curve signature scheme Edwards-curve D <date month="August" year="2015"/>
igital Signature Algorithm (EdDSA). The algorithm is instantiated with recommend </front>
ed parameters for the edwards25519 and edwards448 curves. An example implementat <seriesInfo name="FIPS PUB" value="180-4"/>
ion and test vectors are provided.</t> <seriesInfo name="DOI" value="10.6028/NIST.FIPS.180-4"/>
</abstract> </reference>
</front>
<seriesInfo name='RFC' value='8032'/>
<seriesInfo name='DOI' value='10.17487/RFC8032'/>
</reference>
<reference anchor='RFC8126'> <reference anchor="FIPS202" target="https://nvlpubs.nist.gov/nistpubs/fi
<front> ps/nist.fips.202.pdf">
<title>Guidelines for Writing an IANA Considerations Section in RFCs</title> <front>
<author fullname='M. Cotton' initials='M.' surname='Cotton'/> <title>SHA-3 Standard: Permutation-Based Hash and Extendable-Output
<author fullname='B. Leiba' initials='B.' surname='Leiba'/> Functions</title>
<author fullname='T. Narten' initials='T.' surname='Narten'/> <author>
<date month='June' year='2017'/> <organization>NIST</organization>
<abstract> </author>
<t>Many protocols make use of points of extensibility that use constants t <date month="August" year="2015"/>
o identify various protocol parameters. To ensure that the values in these field </front>
s do not have conflicting uses and to promote interoperability, their allocation <seriesInfo name="FIPS PUB" value="202"/>
s are often coordinated by a central record keeper. For IETF protocols, that rol <seriesInfo name="DOI" value="10.6028/NIST.FIPS.202"/>
e is filled by the Internet Assigned Numbers Authority (IANA).</t> </reference>
<t>To make assignments in a given registry prudently, guidance describing
the conditions under which new values should be assigned, as well as when and ho
w modifications to existing values can be made, is needed. This document defines
a framework for the documentation of these guidelines by specification authors,
in order to assure that the provided guidance for the IANA Considerations is cl
ear and addresses the various issues that are likely in the operation of a regis
try.</t>
<t>This is the third edition of this document; it obsoletes RFC 5226.</t>
</abstract>
</front>
<seriesInfo name='BCP' value='26'/>
<seriesInfo name='RFC' value='8126'/>
<seriesInfo name='DOI' value='10.17487/RFC8126'/>
</reference>
<reference anchor='RFC9106'> </references>
<front> <references>
<title>Argon2 Memory-Hard Function for Password Hashing and Proof-of-Work Ap <name>Informative References</name>
plications</title>
<author fullname='A. Biryukov' initials='A.' surname='Biryukov'/>
<author fullname='D. Dinu' initials='D.' surname='Dinu'/>
<author fullname='D. Khovratovich' initials='D.' surname='Khovratovich'/>
<author fullname='S. Josefsson' initials='S.' surname='Josefsson'/>
<date month='September' year='2021'/>
<abstract>
<t>This document describes the Argon2 memory-hard function for password ha
shing and proof-of-work applications. We provide an implementer-oriented descrip
tion with test vectors. The purpose is to simplify adoption of Argon2 for Intern
et protocols. This document is a product of the Crypto Forum Research Group (CFR
G) in the IRTF.</t>
</abstract>
</front>
<seriesInfo name='RFC' value='9106'/>
<seriesInfo name='DOI' value='10.17487/RFC9106'/>
</reference>
<reference anchor="RIPEMD-160" > <reference anchor="BLEICHENBACHER">
<front> <front>
<title>Information technology - Security techniques - Hash-functions - Part <title>Generating ElGamal Signatures Without Knowing the Secret Key<
3: Dedicated hash-functions,</title> /title>
<author > <author initials="D." surname="Bleichenbacher">
<organization>International Organization for Standardization, Geneva, Swit <organization/>
zerland</organization> </author>
</author> <date month="May" year="1996"/>
<date year="1998"/> </front>
</front> <refcontent>EUROCRYPT'96: International Conference on the Theory and A
<seriesInfo name="ISO" value="ISO/IEC 10118-3"/> pplications of Cryptographic Techniques Proceedings, Vol. 1070, pp. 10-18</refco
</reference> ntent>
<reference anchor="SP800-38A" > </reference>
<front>
<title>Recommendation for Block Cipher Modes of Operation: Methods and Techn
iques</title>
<author initials="M." surname="Dworkin">
<organization></organization>
</author>
<date year="2001" month="December"/>
</front>
<seriesInfo name="NIST Special Publication" value="800-38A"/>
</reference>
<reference anchor="SP800-38D" >
<front>
<title>Recommendation for Block Cipher Modes of Operation: Galois/Counter Mo
de (GCM) and GMAC</title>
<author initials="M." surname="Dworkin">
<organization></organization>
</author>
<date year="2007" month="November"/>
</front>
<seriesInfo name="NIST Special Publication" value="800-38D"/>
</reference>
<reference anchor="SP800-56A" >
<front>
<title>Recommendation for Pair-Wise Key Establishment Schemes Using Discrete
Logarithm Cryptography</title>
<author initials="E." surname="Barker">
<organization></organization>
</author>
<author initials="D." surname="Johnson">
<organization></organization>
</author>
<author initials="M." surname="Smid">
<organization></organization>
</author>
<date year="2007" month="March"/>
</front>
<seriesInfo name="NIST Special Publication" value="800-56A Revision 1"/>
</reference>
<reference anchor="SP800-67" target="https://doi.org/10.6028/NIST.SP.800-67r2">
<front>
<title>Recommendation for the Triple Data Encryption Algorithm (TDEA) Block
Cipher</title>
<author >
<organization>NIST</organization>
</author>
<date year="2017" month="November"/>
</front>
<seriesInfo name="NIST Special Publication" value="800-67 Rev. 2"/>
<seriesInfo name="DOI" value="10.6028/NIST.SP.800-67r2"/>
</reference>
<reference anchor="TWOFISH" target="https://www.schneier.com/wp-content/uploads/
2016/02/paper-twofish-paper.pdf">
<front>
<title>The Twofish Encryption Algorithm</title>
<author initials="B." surname="Schneier">
<organization></organization>
</author>
<author initials="J." surname="Kelsey">
<organization></organization>
</author>
<author initials="D." surname="Whiting">
<organization></organization>
</author>
<author initials="D." surname="Wagner">
<organization></organization>
</author>
<author initials="C." surname="Hall">
<organization></organization>
</author>
<author initials="N." surname="Ferguson">
<organization></organization>
</author>
<date year="1999"/>
</front>
</reference>
<reference anchor='RFC2119'> <reference anchor="BLEICHENBACHER-PKCS1" target="http://archiv.infsec.et
<front> hz.ch/education/fs08/secsem/Bleichenbacher98.pdf">
<title>Key words for use in RFCs to Indicate Requirement Levels</title> <front>
<author fullname='S. Bradner' initials='S.' surname='Bradner'/> <title>Chosen Ciphertext Attacks Against Protocols Based on the RSA
<date month='March' year='1997'/> Encryption Standard PKCS #1</title>
<abstract> <author initials="D." surname="Bleichenbacher">
<t>In many standards track documents several words are used to signify the <organization/>
requirements in the specification. These words are often capitalized. This docu </author>
ment defines these words as they should be interpreted in IETF documents. This d <date month="August" year="1998"/>
ocument specifies an Internet Best Current Practices for the Internet Community, </front>
and requests discussion and suggestions for improvements.</t> <refcontent>CRYPTO '98: International Cryptology Conference Proceedings
</abstract> , Vol. 1462, pp. 1-12</refcontent>
</front> </reference>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='2119'/>
<seriesInfo name='DOI' value='10.17487/RFC2119'/>
</reference>
<reference anchor='RFC8174'> <reference anchor="C99" target="https://www.iso.org/standard/74528.html"
<front> >
<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title> <front>
<author fullname='B. Leiba' initials='B.' surname='Leiba'/> <title>Information technology - Programming languages: C</title>
<date month='May' year='2017'/> <author>
<abstract> <organization>ISO</organization>
<t>RFC 2119 specifies common key words that may be used in protocol specif </author>
ications. This document aims to reduce the ambiguity by clarifying that only UPP <date year="2018" month="June"/>
ERCASE usage of the key words have the defined special meanings.</t> </front>
</abstract> <seriesInfo name="ISO/IEC" value="9899:2018"/>
</front> </reference>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='8174'/>
<seriesInfo name='DOI' value='10.17487/RFC8174'/>
</reference>
<reference anchor='FIPS186'> <reference anchor="EFAIL" target="https://www.usenix.org/system/files/co
<front> nference/usenixsecurity18/sec18-poddebniak.pdf">
<title>Digital Signature Standard (DSS)</title> <front>
<author fullname='Lily Chen' initials='L.' surname='Chen'> <title>Efail: Breaking S/MIME and OpenPGP Email Encryption using Exf
<organization/> iltration Channels</title>
</author> <author initials="D." surname="Poddebniak" fullname="Damian Poddebni
<author fullname='Dustin Moody' initials='D.' surname='Moody'> ak">
<organization/> <organization/>
</author> </author>
<author fullname='Andrew Regenscheid' initials='A.' surname='Regenscheid'> <author initials="C." surname="Dresen" fullname="Christian Dresen">
<organization/> <organization/>
</author> </author>
<author fullname='Angela Robinson' initials='A.' surname='Robinson'> <author initials="J." surname="Müller" fullname="Jens Müller">
<organization/> <organization/>
</author> </author>
<date month='February' year='2023'/> <author initials="F." surname="Ising" fullname="Fabian Ising">
</front> <organization/>
<seriesInfo name='National Institute of Standards and Technology (U.S.)' value </author>
='report'/> <author initials="S." surname="Schinzel" fullname="Sebastian Schinze
<seriesInfo name='DOI' value='10.6028/nist.fips.186-5'/> l">
</reference> <organization/>
</author>
<author initials="S." surname="Friedberger" fullname="Simon Friedber
ger">
<organization/>
</author>
<author initials="J." surname="Somorovsky" fullname="Juraj Somorovsk
y">
<organization/>
</author>
<author initials="J." surname="Schwenk" fullname="Jörg Schwenk">
<organization/>
</author>
<date month="August" year="2018"/>
</front>
<refcontent>Proceedings of the 27th USENIX Security Symposium</refcont
ent>
</reference>
<reference anchor='AES'> <reference anchor="Errata-2199" quote-title="false" target="https://www.rfc-edi tor.org/errata/eid2199">
<front> <front>
<title>Advanced encryption standard (AES)</title> <title>Erratum ID 2199</title>
<author> <author>
<organization/> <organization>RFC Errata</organization>
</author>
<date month='November' year='2001'/>
</front>
<seriesInfo name='National Institute of Standards and Technology' value='repor
t'/>
<seriesInfo name='DOI' value='10.6028/nist.fips.197'/>
</reference>
<reference anchor='FIPS180'>
<front>
<title>Secure Hash Standard</title>
<author fullname='Quynh H. Dang' initials='Q.' surname='Dang'>
<organization/>
</author>
<date month='July' year='2015'/>
</front>
<seriesInfo name='National Institute of Standards and Technology' value='repor
t'/>
<seriesInfo name='DOI' value='10.6028/nist.fips.180-4'/>
</reference>
<reference anchor='FIPS202'>
<front>
<title>SHA-3 Standard: Permutation-Based Hash and Extendable-Output Function
s</title>
<author fullname='Morris J. Dworkin' initials='M.' surname='Dworkin'>
<organization/>
</author> </author>
<date month='July' year='2015'/> <date />
</front> </front>
<seriesInfo name='National Institute of Standards and Technology' value='repor <refcontent>RFC 4880</refcontent>
t'/>
<seriesInfo name='DOI' value='10.6028/nist.fips.202'/>
</reference> </reference>
</references> <reference anchor="Errata-2200" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2200">
<references title='Informative References'>
<reference anchor="BLEICHENBACHER" >
<front>
<title>Generating ElGamal Signatures Without Knowing the Secret Key</title>
<author initials="D." surname="Bleichenbacher">
<organization></organization>
</author>
<date year="1996"/>
</front>
<seriesInfo name="Lecture Notes in Computer Science" value="Volume 1070, pp. 1
0-18"/>
</reference>
<reference anchor="BLEICHENBACHER-PKCS1" target="http://archiv.infsec.ethz.ch/ed
ucation/fs08/secsem/Bleichenbacher98.pdf">
<front>
<title>Chosen Ciphertext Attacks Against Protocols Based on the RSA Encrypti
on Standard PKCS \#1</title>
<author initials="D." surname="Bleichenbacher">
<organization></organization>
</author>
<date year="1998"/>
</front>
</reference>
<reference anchor="C99" target="https://www.iso.org/standard/50510.html">
<front>
<title>Programming languages - C: C99, correction 3:2007, ISO/IEC 9899:1999
/Cor 3:2007</title>
<author initials="I. O. for" surname="Standardization" fullname="Internation
al Organization for Standardization">
<organization></organization>
</author>
<date year="2007" month="November"/>
</front>
</reference>
<reference anchor="EFAIL" target="https://www.usenix.org/system/files/conference
/usenixsecurity18/sec18-poddebniak.pdf">
<front>
<title>Efail: Breaking S/MIME and OpenPGP Email Encryption using Exfiltratio
n Channels</title>
<author initials="D." surname="Poddebniak" fullname="Damian Poddebniak">
<organization></organization>
</author>
<author initials="C." surname="Dresen" fullname="Christian Dresen">
<organization></organization>
</author>
<author initials="J." surname="Müller" fullname="Jens Müller">
<organization></organization>
</author>
<author initials="F." surname="Ising" fullname="Fabian Ising">
<organization></organization>
</author>
<author initials="S." surname="Schinzel" fullname="Sebastian Schinzel">
<organization></organization>
</author>
<author initials="S." surname="Friedberger" fullname="Simon Friedberger">
<organization></organization>
</author>
<author initials="J." surname="Somorovsky" fullname="Juraj Somorovsky">
<organization></organization>
</author>
<author initials="J." surname="Schwenk" fullname="Jörg Schwenk">
<organization></organization>
</author>
<date year="2018"/>
</front>
<seriesInfo name="Proceedings of the 27th USENIX Conference on Security Sympos
ium, August 2018, Pages 549–566" value=""/>
</reference>
<reference anchor="Errata-2199" target="https://www.rfc-editor.org/errata/eid219
9">
<front> <front>
<title>Errata Report 2199 - S2K hash/cipher octet correction</title> <title>Erratum ID 2200</title>
<author > <author>
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2200" target="https://www.rfc-editor.org/errata/eid220
0"> <reference anchor="Errata-2206" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2206">
<front> <front>
<title>Errata Report 2200 - No implicit use of IDEA correction</title> <title>Erratum ID 2206</title>
<author > <author>
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2206" target="https://www.rfc-editor.org/errata/eid220
6"> <reference anchor="Errata-2208" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2208">
<front> <front>
<title>Errata Report 2206 - PKESK acronym expansion</title> <title>Erratum ID 2208</title>
<author > <author>
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2208" target="https://www.rfc-editor.org/errata/eid220
8"> <reference anchor="Errata-2214" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2214">
<front> <front>
<title>Errata Report 2208 - Signature key owner clarification</title> <title>Erratum ID 2214</title>
<author > <author>
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2214" target="https://www.rfc-editor.org/errata/eid221
4"> <reference anchor="Errata-2216" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2216">
<front> <front>
<title>Errata Report 2214 - Signature hashing clarification</title> <title>Erratum ID 2216</title>
<author > <author>
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2216" target="https://www.rfc-editor.org/errata/eid221
6"> <reference anchor="Errata-2219" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2219">
<front> <front>
<title>Errata Report 2216 - Self signature applies to user ID correction</ti <title>Erratum ID 2219</title>
tle> <author>
<author > <organization>RFC Errata</organization>
<organization></organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2219" target="https://www.rfc-editor.org/errata/eid221
9"> <reference anchor="Errata-2222" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2222">
<front> <front>
<title>Errata Report 2219 - Session key encryption storage clarification</ti tle> <title>Erratum ID 2222</title>
<author > <author >
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2222" target="https://www.rfc-editor.org/errata/eid222
2"> <reference anchor="Errata-2226" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2226">
<front> <front>
<title>Errata Report 2222 - Simple hash MUST/MAY clarification</title> <title>Erratum ID 2226</title>
<author > <author >
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2226" target="https://www.rfc-editor.org/errata/eid222
6"> <reference anchor="Errata-2234" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2234">
<front> <front>
<title>Errata Report 2226 - Native line endings SHOULD clarification</title> <title>Erratum ID 2234</title>
<author > <author >
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2234" target="https://www.rfc-editor.org/errata/eid223
4"> <reference anchor="Errata-2235" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2235">
<front> <front>
<title>Errata Report 2234 - Radix-64 / base64 clarification</title> <title>Erratum ID 2235</title>
<author > <author >
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2235" target="https://www.rfc-editor.org/errata/eid223
5"> <reference anchor="Errata-2236" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2236">
<front> <front>
<title>Errata Report 2235 - ASCII / UTF-8 collation sequence clarification</ <title>Erratum ID 2236</title>
title> <author>
<author > <organization>RFC Errata</organization>
<organization></organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2236" target="https://www.rfc-editor.org/errata/eid223
6"> <reference anchor="Errata-2238" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2238">
<front> <front>
<title>Errata Report 2236 - Packet Composition is a sequence clarification</ <title>Erratum ID 2238</title>
title> <author>
<author > <organization>RFC Errata</organization>
<organization></organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2238" target="https://www.rfc-editor.org/errata/eid223
8"> <reference anchor="Errata-2240" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2240">
<front> <front>
<title>Errata Report 2238 - Subkey packets come after all User ID packets cl <title>Erratum ID 2240</title>
arification</title> <author>
<author > <organization>RFC Errata</organization>
<organization></organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2240" target="https://www.rfc-editor.org/errata/eid224
0"> <reference anchor="Errata-2242" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2242">
<front> <front>
<title>Errata Report 2240 - Subkey removal clarification</title> <title>Erratum ID 2242</title>
<author > <author >
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2242" target="https://www.rfc-editor.org/errata/eid224
2"> <reference anchor="Errata-2243" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2243">
<front> <front>
<title>Errata Report 2242 - mL / emLen variable correction</title> <title>Erratum ID 2243</title>
<author > <author>
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2243" target="https://www.rfc-editor.org/errata/eid224
3"> <reference anchor="Errata-2270" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2270">
<front> <front>
<title>Errata Report 2243 - CFB mode initialization vector (IV) clarificatio <title>Erratum ID 2270</title>
n</title> <author>
<author > <organization>RFC Errata</organization>
<organization></organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2270" target="https://www.rfc-editor.org/errata/eid227
0"> <reference anchor="Errata-2271" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid2271">
<front> <front>
<title>Errata Report 2270 - SHA-224 octet sequence correction</title> <title>Erratum ID 2271</title>
<author > <author >
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-2271" target="https://www.rfc-editor.org/errata/eid227
1"> <reference anchor="Errata-3298" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid3298">
<front> <front>
<title>Errata Report 2271 - Radix-64 correction</title> <title>Erratum ID 3298</title>
<author > <author>
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-3298" target="https://www.rfc-editor.org/errata/eid329
8"> <reference anchor="Errata-5491" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid5491">
<front> <front>
<title>Errata Report 3298 - Key revocation signatures correction</title> <title>Erratum ID 5491</title>
<author > <author>
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-5491" target="https://www.rfc-editor.org/errata/eid549
1"> <reference anchor="Errata-7545" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid7545">
<front> <front>
<title>Errata Report 5491 - C code fix for CRC24_POLY define</title> <title>Erratum ID 7545</title>
<author > <author>
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference> </reference>
<reference anchor="Errata-7545" target="https://www.rfc-editor.org/errata/eid754
5"> <reference anchor="Errata-7889" quote-title="false" target="https://www.rfc-edit
or.org/errata/eid7889">
<front> <front>
<title>Errata Report 7545 - Armor Header colon hex fix</title> <title>Erratum ID 7889</title>
<author > <author>
<organization></organization> <organization>RFC Errata</organization>
</author> </author>
<date /> <date />
</front> </front>
<seriesInfo name="RFC" value="4880"/> <refcontent>RFC 4880</refcontent>
</reference>
<reference anchor="HASTAD" >
<front>
<title>Solving Simultaneous Modular Equations of Low Degree</title>
<author initials="J." surname="Hastad" fullname="Johan Hastad">
<organization></organization>
</author>
<date year="1988"/>
</front>
<seriesInfo name="DOI" value="10.1137/0217019"/>
</reference>
<reference anchor="JKS02" target="http://www.counterpane.com/pgp-attack.html">
<front>
<title>Implementation of Chosen-Ciphertext Attacks against PGP and GnuPG</ti
tle>
<author initials="K." surname="Jallad" fullname="Kahil Jallad">
<organization></organization>
</author>
<author initials="J." surname="Katz" fullname="Jonathan Katz">
<organization></organization>
</author>
<author initials="B." surname="Schneier" fullname="Bruce Schneier">
<organization></organization>
</author>
<date year="2002"/>
</front>
</reference>
<reference anchor="KOBLITZ" >
<front>
<title>A course in number theory and cryptography, Chapter VI. Elliptic Curv
es</title>
<author initials="N." surname="Koblitz">
<organization></organization>
</author>
<date year="1997"/>
</front>
<seriesInfo name="ISBN" value="0-387-96576-9"/>
</reference>
<reference anchor="KOPENPGP" target="https://www.kopenpgp.com/">
<front>
<title>Victory by KO: Attacking OpenPGP Using Key Overwriting</title>
<author initials="L." surname="Bruseghini" fullname="Lara Bruseghini">
<organization></organization>
</author>
<author initials="K. G." surname="Paterson" fullname="Kenneth G. Paterson">
<organization></organization>
</author>
<author initials="D." surname="Huigens" fullname="Daniel Huigens">
<organization></organization>
</author>
<date year="2022"/>
</front>
<seriesInfo name="Proceedings of the 29th ACM Conference on Computer and Commu
nications Security, November 2022 (to appear)" value=""/>
</reference>
<reference anchor="KR02" target="https://eprint.iacr.org/2002/076">
<front>
<title>Attack on Private Signature Keys of the OpenPGP Format, PGP(TM) Progr
ams and Other Applications Compatible with OpenPGP</title>
<author initials="V." surname="Klíma" fullname="Vlastimil Klíma">
<organization></organization>
</author>
<author initials="T." surname="Rosa" fullname="Tomáš Rosa">
<organization></organization>
</author>
<date year="2002"/>
</front>
<seriesInfo name="Cryptology ePrint Archive, Report 2002/076" value=""/>
</reference>
<reference anchor="MRLG15" >
<front>
<title>Format Oracles on OpenPGP</title>
<author initials="F." surname="Maury" fullname="Florian Maury">
<organization></organization>
</author>
<author initials="J.-R." surname="Reinhard" fullname="Jean-René Reinhard">
<organization></organization>
</author>
<author initials="O." surname="Levillain" fullname="Olivier Levillain">
<organization></organization>
</author>
<author initials="H." surname="Gilbert" fullname="Henri Gilbert">
<organization></organization>
</author>
<date year="2015"/>
</front>
<seriesInfo name="CT-RSA 2015" value="Topics in Cryptology –- CT-RSA 2015 pp 2
20–236"/>
<seriesInfo name="DOI" value="10.1007/978-3-319-16715-2_12"/>
</reference>
<reference anchor="MZ05" target="http://eprint.iacr.org/2005/033">
<front>
<title>An Attack on CFB Mode Encryption As Used By OpenPGP</title>
<author initials="S." surname="Mister" fullname="Serge Mister">
<organization></organization>
</author>
<author initials="R." surname="Zuccherato" fullname="Robert Zuccherato">
<organization></organization>
</author>
<date year="2005" month="February" day="08"/>
</front>
<seriesInfo name="IACR ePrint Archive" value="Report 2005/033"/>
</reference>
<reference anchor="OPENPGPCARD" target="https://gnupg.org/ftp/specs/OpenPGP-smar
t-card-application-3.4.1.pdf">
<front>
<title>Functional Specification of the OpenPGP application on ISO Smart Card
Operating Systems (version 3.4.1)</title>
<author initials="A." surname="Pietig" fullname="Achim Pietig">
<organization></organization>
</author>
<date year="2020"/>
</front>
</reference>
<reference anchor="PAX" target="https://pubs.opengroup.org/onlinepubs/9699919799
/utilities/pax.html">
<front>
<title>IEEE Standard for Information Technology--Portable Operating System I
nterface (POSIX(R)) Base Specifications, Issue 7: pax - portable archive interch
ange</title>
<author >
<organization>The Open Group</organization>
</author>
<date year="2018"/>
</front>
<seriesInfo name="IEEE Standard" value="1003.1-2017"/>
<seriesInfo name="DOI" value="10.1109/IEEESTD.2018.8277153"/>
</reference>
<reference anchor="PSSLR17" target="https://eprint.iacr.org/2017/1014">
<front>
<title>Attacking Deterministic Signature Schemes using Fault Attacks</title>
<author initials="D." surname="Poddebniak">
<organization></organization>
</author>
<author initials="J." surname="Somorovsky">
<organization></organization>
</author>
<author initials="S." surname="Schinzel">
<organization></organization>
</author>
<author initials="M." surname="Lochter">
<organization></organization>
</author>
<author initials="P." surname="Rösler">
<organization></organization>
</author>
<date year="2017" month="October"/>
</front>
</reference>
<reference anchor="REGEX" >
<front>
<title>Mastering Regular Expressions</title>
<author initials="J." surname="Friedl" fullname="Jeffrey Friedl">
<organization>O'Reilly</organization>
</author>
<date year="2002" month="August"/>
</front>
<seriesInfo name="ISBN" value="0-596-00289-0"/>
</reference> </reference>
<reference anchor='RFC1991'> <reference anchor="HASTAD">
<front> <front>
<title>PGP Message Exchange Formats</title> <title>Solving Simultaneous Modular Equations of Low Degree</title>
<author fullname='D. Atkins' initials='D.' surname='Atkins'/> <author initials="J." surname="Hastad" fullname="Johan Hastad">
<author fullname='W. Stallings' initials='W.' surname='Stallings'/> <organization/>
<author fullname='P. Zimmermann' initials='P.' surname='Zimmermann'/> </author>
<date month='August' year='1996'/> <date month="April" year="1988"/>
<abstract> </front>
<t>This document describes the format of "PGP files", i.e., messages that <seriesInfo name="DOI" value="10.1137/0217019"/>
have been encrypted and/or signed with PGP. This memo provides information for t </reference>
he Internet community. This memo does not specify an Internet standard of any ki
nd.</t>
</abstract>
</front>
<seriesInfo name='RFC' value='1991'/>
<seriesInfo name='DOI' value='10.17487/RFC1991'/>
</reference>
<reference anchor='RFC2440'> <reference anchor="JKS02" target="https://www.schneier.com/academic/arch
<front> ives/2002/01/implementation_of_ch.html">
<title>OpenPGP Message Format</title> <front>
<author fullname='J. Callas' initials='J.' surname='Callas'/> <title>Implementation of Chosen-Ciphertext Attacks against PGP and G
<author fullname='L. Donnerhacke' initials='L.' surname='Donnerhacke'/> nuPG</title>
<author fullname='H. Finney' initials='H.' surname='Finney'/> <author initials="K." surname="Jallad" fullname="Kahil Jallad">
<author fullname='R. Thayer' initials='R.' surname='Thayer'/> <organization/>
<date month='November' year='1998'/> </author>
<abstract> <author initials="J." surname="Katz" fullname="Jonathan Katz">
<t>This document is maintained in order to publish all necessary informati <organization/>
on needed to develop interoperable applications based on the OpenPGP format. [ST </author>
ANDARDS-TRACK]</t> <author initials="B." surname="Schneier" fullname="Bruce Schneier">
</abstract> <organization/>
</front> </author>
<seriesInfo name='RFC' value='2440'/> <date month="September" year="2002"/>
<seriesInfo name='DOI' value='10.17487/RFC2440'/> </front>
</reference> <seriesInfo name="DOI" value="0.1007/3-540-45811-5_7"/>
</reference>
<reference anchor='RFC4880'> <reference anchor="KOBLITZ">
<front> <front>
<title>OpenPGP Message Format</title> <title>A course in number theory and cryptography</title>
<author fullname='J. Callas' initials='J.' surname='Callas'/> <author initials="N." surname="Koblitz">
<author fullname='L. Donnerhacke' initials='L.' surname='Donnerhacke'/> <organization/>
<author fullname='H. Finney' initials='H.' surname='Finney'/> </author>
<author fullname='D. Shaw' initials='D.' surname='Shaw'/> <date year="1997"/>
<author fullname='R. Thayer' initials='R.' surname='Thayer'/> </front>
<date month='November' year='2007'/> <seriesInfo name="DOI" value="10.2307/3618498"/>
<abstract> <refcontent>Chaper VI: Elliptic Curves</refcontent>
<t>This document is maintained in order to publish all necessary informati </reference>
on needed to develop interoperable applications based on the OpenPGP format. It
is not a step-by-step cookbook for writing an application. It describes only the
format and methods needed to read, check, generate, and write conforming packet
s crossing any network. It does not deal with storage and implementation questio
ns. It does, however, discuss implementation issues necessary to avoid security
flaws.</t>
<t>OpenPGP software uses a combination of strong public-key and symmetric
cryptography to provide security services for electronic communications and data
storage. These services include confidentiality, key management, authentication
, and digital signatures. This document specifies the message formats used in Op
enPGP. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name='RFC' value='4880'/>
<seriesInfo name='DOI' value='10.17487/RFC4880'/>
</reference>
<reference anchor='RFC5581'> <reference anchor="KOPENPGP" target="https://dl.acm.org/doi/10.1145/3548
<front> 606.3559363">
<title>The Camellia Cipher in OpenPGP</title> <front>
<author fullname='D. Shaw' initials='D.' surname='Shaw'/> <title>Victory by KO: Attacking OpenPGP Using Key Overwriting</title
<date month='June' year='2009'/> >
<abstract> <author initials="L." surname="Bruseghini" fullname="Lara Bruseghini
<t>This document presents the necessary information to use the Camellia sy ">
mmetric block cipher in the OpenPGP protocol. This memo provides information for <organization/>
the Internet community.</t> </author>
</abstract> <author initials="K. G." surname="Paterson" fullname="Kenneth G. Pat
</front> erson">
<seriesInfo name='RFC' value='5581'/> <organization/>
<seriesInfo name='DOI' value='10.17487/RFC5581'/> </author>
</reference> <author initials="D." surname="Huigens" fullname="Daniel Huigens">
<organization/>
</author>
<date month="November" year="2022"/>
</front>
<seriesInfo name="DOI" value="10.1145/3548606.3559363"/>
<refcontent>Proceedings of the ACM SIGSAC Conference on Computer and C
ommunications Security, pp. 411-423</refcontent>
</reference>
<reference anchor='RFC5639'> <reference anchor="KR02" target="https://eprint.iacr.org/2002/076">
<front> <front>
<title>Elliptic Curve Cryptography (ECC) Brainpool Standard Curves and Curve <title>Attack on Private Signature Keys of the OpenPGP Format, PGP(T
Generation</title> M) Programs and Other Applications Compatible with OpenPGP</title>
<author fullname='M. Lochter' initials='M.' surname='Lochter'/> <author initials="V." surname="Klíma" fullname="Vlastimil Klíma">
<author fullname='J. Merkle' initials='J.' surname='Merkle'/> <organization/>
<date month='March' year='2010'/> </author>
<abstract> <author initials="T." surname="Rosa" fullname="Tomáš Rosa">
<t>This memo proposes several elliptic curve domain parameters over finite <organization/>
prime fields for use in cryptographic applications. The domain parameters are c </author>
onsistent with the relevant international standards, and can be used in X.509 ce <date month="March" year="2001"/>
rtificates and certificate revocation lists (CRLs), for Internet Key Exchange (I </front>
KE), Transport Layer Security (TLS), XML signatures, and all applications or pro <refcontent>Cryptology ePrint Archive, Paper 2002/076</refcontent>
tocols based on the cryptographic message syntax (CMS). This document is not an </reference>
Internet Standards Track specification; it is published for informational purpos
es.</t>
</abstract>
</front>
<seriesInfo name='RFC' value='5639'/>
<seriesInfo name='DOI' value='10.17487/RFC5639'/>
</reference>
<reference anchor='RFC5869'> <reference anchor="MRLG15">
<front> <front>
<title>HMAC-based Extract-and-Expand Key Derivation Function (HKDF)</title> <title>Format Oracles on OpenPGP</title>
<author fullname='H. Krawczyk' initials='H.' surname='Krawczyk'/> <author initials="F." surname="Maury" fullname="Florian Maury">
<author fullname='P. Eronen' initials='P.' surname='Eronen'/> <organization/>
<date month='May' year='2010'/> </author>
<abstract> <author initials="JR." surname="Reinhard" fullname="Jean-René Reinha
<t>This document specifies a simple Hashed Message Authentication Code (HM rd">
AC)-based key derivation function (HKDF), which can be used as a building block <organization/>
in various protocols and applications. The key derivation function (KDF) is inte </author>
nded to support a wide range of applications and requirements, and is conservati <author initials="O." surname="Levillain" fullname="Olivier Levillai
ve in its use of cryptographic hash functions. This document is not an Internet n">
Standards Track specification; it is published for informational purposes.</t> <organization/>
</abstract> </author>
</front> <author initials="H." surname="Gilbert" fullname="Henri Gilbert">
<seriesInfo name='RFC' value='5869'/> <organization/>
<seriesInfo name='DOI' value='10.17487/RFC5869'/> </author>
</reference> <date month="January" year="2015"/>
</front>
<seriesInfo name="DOI" value="10.1007/978-3-319-16715-2_12"/>
<refcontent>Topics in Cryptology -- CT-RSA 2015, Vol. 9048, pp. 220-236
</refcontent>
</reference>
<reference anchor='RFC6090'> <reference anchor="MZ05" target="http://eprint.iacr.org/2005/033">
<front> <front>
<title>Fundamental Elliptic Curve Cryptography Algorithms</title> <title>An Attack on CFB Mode Encryption As Used By OpenPGP</title>
<author fullname='D. McGrew' initials='D.' surname='McGrew'/> <author initials="S." surname="Mister" fullname="Serge Mister">
<author fullname='K. Igoe' initials='K.' surname='Igoe'/> <organization/>
<author fullname='M. Salter' initials='M.' surname='Salter'/> </author>
<date month='February' year='2011'/> <author initials="R." surname="Zuccherato" fullname="Robert Zucchera
<abstract> to">
<t>This note describes the fundamental algorithms of Elliptic Curve Crypto <organization/>
graphy (ECC) as they were defined in some seminal references from 1994 and earli </author>
er. These descriptions may be useful for implementing the fundamental algorithms <date year="2005" month="February"/>
without using any of the specialized methods that were developed in following y </front>
ears. Only elliptic curves defined over fields of characteristic greater than th <refcontent>Cryptology ePrint Archive, Paper 2005/033</refcontent>
ree are in scope; these curves are those used in Suite B. This document is not a </reference>
n Internet Standards Track specification; it is published for informational purp
oses.</t>
</abstract>
</front>
<seriesInfo name='RFC' value='6090'/>
<seriesInfo name='DOI' value='10.17487/RFC6090'/>
</reference>
<reference anchor='RFC6637'> <reference anchor="OPENPGPCARD" target="https://gnupg.org/ftp/specs/Open
<front> PGP-smart-card-application-3.4.1.pdf">
<title>Elliptic Curve Cryptography (ECC) in OpenPGP</title> <front>
<author fullname='A. Jivsov' initials='A.' surname='Jivsov'/> <title>Functional Specification of the OpenPGP application on ISO Sm
<date month='June' year='2012'/> art Card Operating Systems</title>
<abstract> <author initials="A." surname="Pietig" fullname="Achim Pietig">
<t>This document defines an Elliptic Curve Cryptography extension to the O <organization/>
penPGP public key format and specifies three Elliptic Curves that enjoy broad su </author>
pport by other standards, including standards published by the US National Insti <date month="March" year="2020"/>
tute of Standards and Technology. The document specifies the conventions for int </front>
eroperability between compliant OpenPGP implementations that make use of this ex <refcontent>Version 3.4.1</refcontent>
tension and these Elliptic Curves. [STANDARDS-TRACK]</t> </reference>
</abstract>
</front>
<seriesInfo name='RFC' value='6637'/>
<seriesInfo name='DOI' value='10.17487/RFC6637'/>
</reference>
<reference anchor="SEC1" target="https://www.secg.org/sec1-v2.pdf"> <reference anchor="PAX" target="https://pubs.opengroup.org/onlinepubs/
<front> 9699919799/utilities/pax.html">
<title>Standards for Efficient Cryptography 1 (SEC 1)</title> <front>
<author > <title>The Open Group Base Specifications</title>
<organization>Standards for Efficient Cryptography Group</organization> <author>
</author> <organization>The Open Group</organization>
<date year="2009" month="May"/> </author>
</front> <date year="2018"/>
</reference> </front>
<reference anchor="SHA1CD" target="https://github.com/cr-marcstevens/sha1collisi <seriesInfo name="IEEE Std" value="1003.1-2017"/>
ondetection"> <refcontent>'pax - portable archive interchange', Issue 7, 2018 Editio
<front> n </refcontent>
<title>sha1collisiondetection</title> </reference>
<author initials="M." surname="Stevens" fullname="Marc Stevens">
<organization></organization>
</author>
<author initials="D." surname="Shumow" fullname="Dan Shumow">
<organization></organization>
</author>
<date year="2017"/>
</front>
</reference>
<reference anchor="SHAMBLES" target="https://sha-mbles.github.io/">
<front>
<title>Sha-1 is a shambles: First chosen-prefix collision on sha-1 and appli
cation to the PGP web of trust</title>
<author initials="G." surname="Leurent" fullname="Gaëtan Leurent">
<organization></organization>
</author>
<author initials="T." surname="Peyrin" fullname="Thomas Peyrin">
<organization></organization>
</author>
<date year="2020"/>
</front>
</reference>
<reference anchor="SP800-57" target="https://nvlpubs.nist.gov/nistpubs/SpecialPu
blications/NIST.SP.800-57pt1r5.pdf">
<front>
<title>Recommendation on Key Management: Part 1 - General</title>
<author >
<organization>NIST</organization>
</author>
<date year="2020" month="May"/>
</front>
<seriesInfo name="NIST Special Publication" value="800-57 Part 1 Rev. 5"/>
<seriesInfo name="DOI" value="10.6028/NIST.SP.800-57pt1r5"/>
</reference>
<reference anchor="SP800-131A" target="https://nvlpubs.nist.gov/nistpubs/Special
Publications/NIST.SP.800-131Ar2.pdf">
<front>
<title>Transitioning the Use of Cryptographic Algorithms and Key Lengths</ti
tle>
<author initials="E." surname="Barker">
<organization></organization>
</author>
<author initials="A." surname="Roginsky">
<organization></organization>
</author>
<date year="2019" month="March"/>
</front>
<seriesInfo name="NIST Special Publication" value="800-131A Revision 2"/>
</reference>
<reference anchor="STEVENS2013" target="https://eprint.iacr.org/2013/358">
<front>
<title>Counter-cryptanalysis</title>
<author initials="M." surname="Stevens" fullname="Marc Stevens">
<organization></organization>
</author>
<date year="2013" month="June"/>
</front>
</reference>
<reference anchor="UNIFIED-DIFF" target="https://www.gnu.org/software/diffutils/
manual/html_node/Detailed-Unified.html">
<front>
<title>Detailed Description of Unified Format</title>
<author >
<organization>Free Software Foundation</organization>
</author>
<date year="2021" month="January" day="02"/>
</front>
</reference>
<reference anchor="USENIX-STUDY" target="https://www.usenix.org/system/files/con
ference/usenixsecurity16/sec16_paper_dechand.pdf">
<front>
<title>An Empirical Study of Textual Key-Fingerprint Representations</title>
<author >
<organization>Usenix</organization>
</author>
<date year="2016" month="August" day="10"/>
</front>
<seriesInfo name="ISBN" value="978-1-931971-32-4"/>
</reference>
<reference anchor='RFC2978'> <reference anchor="PSSLR17" target="https://eprint.iacr.org/2017/1014">
<front> <front>
<title>IANA Charset Registration Procedures</title> <title>Attacking Deterministic Signature Schemes using Fault Attacks
<author fullname='N. Freed' initials='N.' surname='Freed'/> </title>
<author fullname='J. Postel' initials='J.' surname='Postel'/> <author initials="D." surname="Poddebniak">
<date month='October' year='2000'/> <organization/>
<abstract> </author>
<t>Multipurpose Internet Mail Extensions (MIME) and various other Internet <author initials="J." surname="Somorovsky">
protocols are capable of using many different charsets. This in turn means that <organization/>
the ability to label different charsets is essential. This document specifies a </author>
n Internet Best Current Practices for the Internet Community, and requests discu <author initials="S." surname="Schinzel">
ssion and suggestions for improvements.</t> <organization/>
</abstract> </author>
</front> <author initials="M." surname="Lochter">
<seriesInfo name='BCP' value='19'/> <organization/>
<seriesInfo name='RFC' value='2978'/> </author>
<seriesInfo name='DOI' value='10.17487/RFC2978'/> <author initials="P." surname="Rösler">
</reference> <organization/>
</author>
<date year="2017" month="October"/>
</front>
<refcontent>Cryptology ePrint Archive, Paper 2017/1014 </refcontent>
</reference>
<reference anchor='CHECKOWAY'> <reference anchor="REGEX" target="https://garyhouston.github.io/regex/">
<front> <front>
<title>A Systematic Analysis of the Juniper Dual EC Incident</title> <title>Henry Spencer's regular expression libraries</title>
<author fullname='Stephen Checkoway' initials='S.' surname='Checkoway'> <author>
<organization>University of Illinois at Chicago, Chicago, IL, USA</organiz <organization>regex</organization>
ation> </author>
</author> <date/>
<author fullname='Jacob Maskiewicz' initials='J.' surname='Maskiewicz'> </front>
<organization>UC San Diego, La Jolla, CA, USA</organization> </reference>
</author>
<author fullname='Christina Garman' initials='C.' surname='Garman'>
<organization>Johns Hopkins University, Baltimore, MD, USA</organization>
</author>
<author fullname='Joshua Fried' initials='J.' surname='Fried'>
<organization>University of Pennsylvania, Philadelphia, PA, USA</organizat
ion>
</author>
<author fullname='Shaanan Cohney' initials='S.' surname='Cohney'>
<organization>University of Pennsylvania, Philadelphia, PA, USA</organizat
ion>
</author>
<author fullname='Matthew Green' initials='M.' surname='Green'>
<organization>Johns Hopkins University, Baltimore, MD, USA</organization>
</author>
<author fullname='Nadia Heninger' initials='N.' surname='Heninger'>
<organization>University of Pennsylvania, Philadelphia, PA, USA</organizat
ion>
</author>
<author fullname='Ralf-Philipp Weinmann' initials='R.' surname='Weinmann'>
<organization>Comsecuris, Duisburg, Germany</organization>
</author>
<author fullname='Eric Rescorla' initials='E.' surname='Rescorla'>
<organization>UC San Diego, La Jolla, CA, USA</organization>
</author>
<author fullname='Hovav Shacham' initials='H.' surname='Shacham'>
<organization>UC San Diego, La Jolla, CA, USA</organization>
</author>
<date month='October' year='2016'/>
</front>
<seriesInfo name='Proceedings of the 2016 ACM SIGSAC Conference on Computer an
d Communications' value='Security'/>
<seriesInfo name='DOI' value='10.1145/2976749.2978395'/>
</reference>
</references> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.1
991.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
440.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
880.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
581.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
639.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
869.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
090.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
637.xml"/>
<section anchor="test-vectors"><name>Test vectors</name> <reference anchor="SEC1" target="https://www.secg.org/sec1-v2.pdf">
<front>
<title>SEC 1: Elliptic Curve Cryptography</title>
<author>
<organization>Standards for Efficient Cryptography Group</organiza
tion>
</author>
<date year="2009" month="May"/>
</front>
<refcontent></refcontent>
</reference>
<t>To help implementing this specification a set of non-normative examples follo <reference anchor="SHA1CD" target="https://github.com/cr-marcstevens/sha
w here.</t> 1collisiondetection">
<front>
<title>sha1collisiondetection</title>
<author>
<organization/>
</author>
<date month="December" year="2020"/>
</front>
<refcontent>commit b4a7b0b</refcontent>
</reference>
<section anchor="sample-v4-ed25519legacy-key"><name>Sample v4 Ed25519Legacy key< <reference anchor="SHAMBLES" target="https://dl.acm.org/doi/abs/10.5555/
/name> 3489212.3489316/">
<front>
<title>Sha-1 is a shambles: first chosen-prefix collision on sha-1 a
nd application to the PGP web of trust</title>
<author initials="G." surname="Leurent" fullname="Gaëtan Leurent">
<organization/>
</author>
<author initials="T." surname="Peyrin" fullname="Thomas Peyrin">
<organization/>
</author>
<date month="August" year="2020"/>
</front>
</reference>
<t>The secret key used for this example is:</t> <reference anchor="SP800-57" target="https://nvlpubs.nist.gov/nistpubs/S
pecialPublications/NIST.SP.800-57pt1r5.pdf">
<front>
<title>Recommendation for Key Management: Part 1 - General</title>
<author>
<organization>NIST</organization>
</author>
<date year="2020" month="May"/>
</front>
<seriesInfo name="NIST Special Publication" value="800-57 Part 1, Revi
sion 5"/>
<seriesInfo name="DOI" value="10.6028/NIST.SP.800-57pt1r5"/>
</reference>
<t>D: 1a8b1ff05ded48e18bf50166c664ab023ea70003d78d9e41f5758a91d850f8d2</t> <reference anchor="SP800-131A" target="https://nvlpubs.nist.gov/nistpubs
/SpecialPublications/NIST.SP.800-131Ar2.pdf">
<front>
<title>Transitioning the Use of Cryptographic Algorithms and Key Len
gths</title>
<author>
<organization>NIST</organization>
</author>
<date year="2019" month="March"/>
</front>
<seriesInfo name="NIST Special Publication" value="800-131A, Revision
2"/>
<seriesInfo name="DOI" value="10.6028/NIST.SP.800-131Ar2"/>
</reference>
<t>Note that this is the raw secret key used as input to the EdDSA signing opera <reference anchor="STEVENS2013" target="https://eprint.iacr.org/2013/358
tion. ">
The key was created on 2014-08-19 14:28:27 and thus the fingerprint of the OpenP <front>
GP key is:</t> <title>Counter-cryptanalysis</title>
<author initials="M." surname="Stevens" fullname="Marc Stevens">
<organization/>
</author>
<date year="2013" month="June"/>
</front>
<refcontent>Cryptology ePrint Archive, Paper 2013/358</refcontent>
</reference>
<figure><artwork><![CDATA[ <reference anchor="UNIFIED-DIFF" target="https://www.gnu.org/software/di
C959 BDBA FA32 A2F8 9A15 3B67 8CFD E121 9796 5A9A ffutils/manual/html_node/Detailed-Unified.html">
]]></artwork></figure> <front>
<title>Comparing and Merging Files</title>
<author>
<organization>Free Software Foundation</organization>
</author>
<date year="2021" month="January"/>
</front>
<refcontent>'Detailed Description of Unified Format', Section 2.2.2.2</
refcontent>
</reference>
<t>The algorithm-specific input parameters without the MPI length headers are:</ <reference anchor="USENIX-STUDY" target="https://www.usenix.org/system/f
t> iles/conference/usenixsecurity16/sec16_paper_dechand.pdf">
<front>
<title>An Empirical Study of Textual Key-Fingerprint Representations
</title>
<author fullname="Sergej Dechand" initials="S." surname="Dechand">
<organization/>
</author>
<author fullname="Dominik Schürmann" initials="D." surname="Schürman
n">
<organization/>
</author>
<author fullname="Karoline Busse" initials="K." surname="Busse">
<organization/>
</author>
<author fullname="Yasemin Acar" initials="Y." surname="Acar">
<organization/>
</author>
<author fullname="Sascha Fahl" initials="S." surname="Fahl">
<organization/>
</author>
<author fullname="Matthew Smith" initials="M." surname="Smith">
<organization/>
</author>
<date year="2016" month="August"/>
</front>
<seriesInfo name="ISBN" value="978-1-931971-32-4"/>
</reference>
<figure><artwork><![CDATA[ <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
oid: 2b06010401da470f01 978.xml"/>
q: 403f098994bdd916ed4053197934e4a87c80733a1280d62f8010992e43ee3b2406 <reference anchor="CHECKOWAY">
]]></artwork></figure> <front>
<title>A Systematic Analysis of the Juniper Dual EC Incident</title>
<author fullname="Stephen Checkoway" initials="S." surname="Checkowa
y">
<organization>University of Illinois at Chicago, Chicago, IL, USA<
/organization>
</author>
<author fullname="Jacob Maskiewicz" initials="J." surname="Maskiewic
z">
<organization>UC San Diego, La Jolla, CA, USA</organization>
</author>
<author fullname="Christina Garman" initials="C." surname="Garman">
<organization>Johns Hopkins University, Baltimore, MD, USA</organi
zation>
</author>
<author fullname="Joshua Fried" initials="J." surname="Fried">
<organization>University of Pennsylvania, Philadelphia, PA, USA</o
rganization>
</author>
<author fullname="Shaanan Cohney" initials="S." surname="Cohney">
<organization>University of Pennsylvania, Philadelphia, PA, USA</o
rganization>
</author>
<author fullname="Matthew Green" initials="M." surname="Green">
<organization>Johns Hopkins University, Baltimore, MD, USA</organi
zation>
</author>
<author fullname="Nadia Heninger" initials="N." surname="Heninger">
<organization>University of Pennsylvania, Philadelphia, PA, USA</o
rganization>
</author>
<author fullname="Ralf-Philipp Weinmann" initials="RP." surname="Wei
nmann">
<organization>Comsecuris, Duisburg, Germany</organization>
</author>
<author fullname="Eric Rescorla" initials="E." surname="Rescorla">
<organization>UC San Diego, La Jolla, CA, USA</organization>
</author>
<author fullname="Hovav Shacham" initials="H." surname="Shacham">
<organization>UC San Diego, La Jolla, CA, USA</organization>
</author>
<date month="October" year="2016"/>
</front>
<refcontent>Proceedings of the 2016 ACM SIGSAC Conference on Computer
and Communications Security</refcontent>
<seriesInfo name="DOI" value="10.1145/2976749.2978395"/>
</reference>
<t>The entire public key packet is thus:</t> </references>
</references>
<section anchor="test-vectors">
<name>Test Vectors</name>
<t>To help with the implementation of this specification, a set of non-nor
mative examples follow.</t>
<section anchor="sample-v4-ed25519legacy-key">
<name>Sample Version 4 Ed25519Legacy Key</name>
<t>The secret key used for this example is:</t>
<artwork><![CDATA[
D: 1a8b1ff05ded48e18bf50166c664ab023ea70003d78d9e41f5758a91d850f8d2
]]></artwork>
<t>Note that this is the raw secret key used as input to the EdDSA signi
ng operation.
The key was created on 2014-08-19 14:28:27 and thus the fingerprint of the OpenP
GP Key is:</t>
<artwork><![CDATA[
C959 BDBA FA32 A2F8 9A15 3B67 8CFD E121 9796 5A9A
]]></artwork>
<t>The algorithm-specific input parameters without the MPI length header
s are:</t>
<artwork><![CDATA[
oid: 2b06010401da470f01
<figure><artwork><![CDATA[ q: 403f098994bdd916ed4053197934e4a87c80733a1280d62f8010992e43ee3b2406
]]></artwork>
<t>The entire Public Key packet is thus:</t>
<artwork><![CDATA[
98 33 04 53 f3 5f 0b 16 09 2b 06 01 04 01 da 47 98 33 04 53 f3 5f 0b 16 09 2b 06 01 04 01 da 47
0f 01 01 07 40 3f 09 89 94 bd d9 16 ed 40 53 19 0f 01 01 07 40 3f 09 89 94 bd d9 16 ed 40 53 19
79 34 e4 a8 7c 80 73 3a 12 80 d6 2f 80 10 99 2e 79 34 e4 a8 7c 80 73 3a 12 80 d6 2f 80 10 99 2e
43 ee 3b 24 06 43 ee 3b 24 06
]]></artwork></figure> ]]></artwork>
<t>The same packet represented in ASCII-armored form is:</t>
<t>The same packet, represented in ASCII-armored form is:</t> <sourcecode type="application/pgp-keys" name="v4-ed25519-pubkey-packet.k
ey"><![CDATA[
<figure><sourcecode type="application/pgp-keys" name="v4-ed25519-pubkey-packet.k
ey"><![CDATA[
-----BEGIN PGP PUBLIC KEY BLOCK----- -----BEGIN PGP PUBLIC KEY BLOCK-----
xjMEU/NfCxYJKwYBBAHaRw8BAQdAPwmJlL3ZFu1AUxl5NOSofIBzOhKA1i+AEJku xjMEU/NfCxYJKwYBBAHaRw8BAQdAPwmJlL3ZFu1AUxl5NOSofIBzOhKA1i+AEJku
Q+47JAY= Q+47JAY=
-----END PGP PUBLIC KEY BLOCK----- -----END PGP PUBLIC KEY BLOCK-----
]]></sourcecode></figure> ]]></sourcecode>
</section>
</section> <section anchor="sample-v4-ed25519legacy-signature">
<section anchor="sample-v4-ed25519legacy-signature"><name>Sample v4 Ed25519Legac <name>Sample Version 4 Ed25519Legacy Signature</name>
y signature</name> <t>The signature is created using the sample key over the input data "Op
enPGP" on 2015-09-16 12:24:53 UTC and thus the input to the hash function is:</t
<t>The signature is created using the sample key over the input data "OpenPGP" o >
n 2015-09-16 12:24:53 UTC and thus the input to the hash function is:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
m: 4f70656e504750040016080006050255f95f9504ff0000000c m: 4f70656e504750040016080006050255f95f9504ff0000000c
]]></artwork></figure> ]]></artwork>
<t>Using the SHA2-256 hash algorithm yields the digest:</t>
<t>Using the SHA2-256 hash algorithm yields the digest:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d: f6220a3f757814f4c2176ffbb68b00249cd4ccdc059c4b34ad871f30b1740280 d: f6220a3f757814f4c2176ffbb68b00249cd4ccdc059c4b34ad871f30b1740280
]]></artwork></figure> ]]></artwork>
<t>which is fed into the EdDSA signature function and yields the followi
<t>Which is fed into the EdDSA signature function and yields this signature:</t> ng signature:</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
r: 56f90cca98e2102637bd983fdb16c131dfd27ed82bf4dde5606e0d756aed3366 r: 56f90cca98e2102637bd983fdb16c131dfd27ed82bf4dde5606e0d756aed3366
s: d09c4fa11527f038e0f57f2201d82f2ea2c9033265fa6ceb489e854bae61b404 s: d09c4fa11527f038e0f57f2201d82f2ea2c9033265fa6ceb489e854bae61b404
]]></artwork></figure> ]]></artwork>
<t>The entire Signature packet is thus:</t>
<t>The entire signature packet is thus:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
88 5e 04 00 16 08 00 06 05 02 55 f9 5f 95 00 0a 88 5e 04 00 16 08 00 06 05 02 55 f9 5f 95 00 0a
09 10 8c fd e1 21 97 96 5a 9a f6 22 00 ff 56 f9 09 10 8c fd e1 21 97 96 5a 9a f6 22 00 ff 56 f9
0c ca 98 e2 10 26 37 bd 98 3f db 16 c1 31 df d2 0c ca 98 e2 10 26 37 bd 98 3f db 16 c1 31 df d2
7e d8 2b f4 dd e5 60 6e 0d 75 6a ed 33 66 01 00 7e d8 2b f4 dd e5 60 6e 0d 75 6a ed 33 66 01 00
d0 9c 4f a1 15 27 f0 38 e0 f5 7f 22 01 d8 2f 2e d0 9c 4f a1 15 27 f0 38 e0 f5 7f 22 01 d8 2f 2e
a2 c9 03 32 65 fa 6c eb 48 9e 85 4b ae 61 b4 04 a2 c9 03 32 65 fa 6c eb 48 9e 85 4b ae 61 b4 04
]]></artwork></figure> ]]></artwork>
<t>The same packet represented in ASCII-armored form is:</t>
<t>The same packet represented in ASCII-armored form is:</t> <sourcecode type="application/pgp-signature" name="v4-ed25519-signature-
over-OpenPGP.sig"><![CDATA[
<figure><sourcecode type="application/pgp-signature" name="v4-ed25519-signature-
over-OpenPGP.sig"><![CDATA[
-----BEGIN PGP SIGNATURE----- -----BEGIN PGP SIGNATURE-----
iF4EABYIAAYFAlX5X5UACgkQjP3hIZeWWpr2IgD/VvkMypjiECY3vZg/2xbBMd/S iF4EABYIAAYFAlX5X5UACgkQjP3hIZeWWpr2IgD/VvkMypjiECY3vZg/2xbBMd/S
ftgr9N3lYG4NdWrtM2YBANCcT6EVJ/A44PV/IgHYLy6iyQMyZfps60iehUuuYbQE ftgr9N3lYG4NdWrtM2YBANCcT6EVJ/A44PV/IgHYLy6iyQMyZfps60iehUuuYbQE
-----END PGP SIGNATURE----- -----END PGP SIGNATURE-----
]]></sourcecode></figure> ]]></sourcecode>
</section>
</section> <section anchor="v6-cert">
<section anchor="v6-cert"><name>Sample v6 Certificate (Transferable Public Key)< <name>Sample Version 6 Certificate (Transferable Public Key)</name>
/name> <t>Here is a Transferable Public Key consisting of:</t>
<ul spacing="normal">
<t>Here is a Transferable Public Key consisting of:</t> <li>
<t>A version 6 Ed25519 Public Key packet</t>
<t><list style="symbols"> </li>
<t>A v6 Ed25519 Public-Key packet</t> <li>
<t>A v6 direct key self-signature</t> <t>A version 6 Direct Key self-signature</t>
<t>A v6 X25519 Public-Subkey packet</t> </li>
<t>A v6 subkey binding signature</t> <li>
</list></t> <t>A version 6 X25519 Public Subkey packet</t>
</li>
<t>The primary key has the fingerprint <spanx style="verb">CB186C4F0609A697E4D52 <li>
DFA6C722B0C1F1E27C18A56708F6525EC27BAD9ACC9</spanx>.</t> <t>A version 6 Subkey Binding signature</t>
</li>
<t>The subkey has the fingerprint <spanx style="verb">12C83F1E706F6308FE151A4177 </ul>
43A1F033790E93E9978488D1DB378DA9930885</spanx>.</t> <t>The primary key has the following fingerprint:</t> <t><tt>CB186C4F060
9A697E4D52DFA6C722B0C1F1E27C18A56708F6525EC27BAD9ACC9</tt></t>
<figure><sourcecode type="application/pgp-keys" name="v6-minimal-cert.key"><![CD <t>The subkey has the following fingerprint:</t> <t><tt>12C83F1E706F6308
ATA[ FE151A417743A1F033790E93E9978488D1DB378DA9930885</tt></t>
<sourcecode type="application/pgp-keys" name="v6-minimal-cert.key"><![CD
ATA[
-----BEGIN PGP PUBLIC KEY BLOCK----- -----BEGIN PGP PUBLIC KEY BLOCK-----
xioGY4d/4xsAAAAg+U2nu0jWCmHlZ3BqZYfQMxmZu52JGggkLq2EVD34laPCsQYf xioGY4d/4xsAAAAg+U2nu0jWCmHlZ3BqZYfQMxmZu52JGggkLq2EVD34laPCsQYf
GwoAAABCBYJjh3/jAwsJBwUVCg4IDAIWAAKbAwIeCSIhBssYbE8GCaaX5NUt+mxy GwoAAABCBYJjh3/jAwsJBwUVCg4IDAIWAAKbAwIeCSIhBssYbE8GCaaX5NUt+mxy
KwwfHifBilZwj2Ul7Ce62azJBScJAgcCAAAAAK0oIBA+LX0ifsDm185Ecds2v8lw KwwfHifBilZwj2Ul7Ce62azJBScJAgcCAAAAAK0oIBA+LX0ifsDm185Ecds2v8lw
gyU2kCcUmKfvBXbAf6rhRYWzuQOwEn7E/aLwIwRaLsdry0+VcallHhSu4RN6HWaE gyU2kCcUmKfvBXbAf6rhRYWzuQOwEn7E/aLwIwRaLsdry0+VcallHhSu4RN6HWaE
QsiPlR4zxP/TP7mhfVEe7XWPxtnMUMtf15OyA51YBM4qBmOHf+MZAAAAIIaTJINn QsiPlR4zxP/TP7mhfVEe7XWPxtnMUMtf15OyA51YBM4qBmOHf+MZAAAAIIaTJINn
+eUBXbki+PSAld2nhJh/LVmFsS+60WyvXkQ1wpsGGBsKAAAALAWCY4d/4wKbDCIh +eUBXbki+PSAld2nhJh/LVmFsS+60WyvXkQ1wpsGGBsKAAAALAWCY4d/4wKbDCIh
BssYbE8GCaaX5NUt+mxyKwwfHifBilZwj2Ul7Ce62azJAAAAAAQBIKbpGG2dWTX8 BssYbE8GCaaX5NUt+mxyKwwfHifBilZwj2Ul7Ce62azJAAAAAAQBIKbpGG2dWTX8
j+VjFM21J0hqWlEg+bdiojWnKfA5AQpWUWtnNwDEM0g12vYxoWM8Y81W+bHBw805 j+VjFM21J0hqWlEg+bdiojWnKfA5AQpWUWtnNwDEM0g12vYxoWM8Y81W+bHBw805
I8kWVkXU6vFOi+HWvv/ira7ofJu16NnoUkhclkUrk0mXubZvyl4GBg== I8kWVkXU6vFOi+HWvv/ira7ofJu16NnoUkhclkUrk0mXubZvyl4GBg==
-----END PGP PUBLIC KEY BLOCK----- -----END PGP PUBLIC KEY BLOCK-----
]]></sourcecode></figure> ]]></sourcecode>
<t>The corresponding Transferable Secret Key can be found in <xref targe
<t>The corresponding Transferable Secret Key can be found in <xref target="v6-ke t="v6-key"/>.</t>
y"/>.</t> <section anchor="sig-hashed-data-example">
<name>Hashed Data Stream for Signature Verification</name>
<section anchor="sig-hashed-data-example"><name>Hashed Data Stream for Signature <t>The Direct Key self-signature in the certificate in <xref target="v
Verification</name> 6-cert"/> is made over the following sequence of data:</t>
<artwork><![CDATA[
<t>The direct key self-signature in the certificate in <xref target="v6-cert"/>
is made over the following sequence of data:</t>
<figure><artwork><![CDATA[
0x0000 10 3e 2d 7d 22 7e c0 e6 0x0000 10 3e 2d 7d 22 7e c0 e6
0x0008 d7 ce 44 71 db 36 bf c9 0x0008 d7 ce 44 71 db 36 bf c9
0x0010 70 83 25 36 90 27 14 98 0x0010 70 83 25 36 90 27 14 98
0x0018 a7 ef 05 76 c0 7f aa e1 0x0018 a7 ef 05 76 c0 7f aa e1
0x0020 9b 00 00 00 2a 06 63 87 0x0020 9b 00 00 00 2a 06 63 87
0x0028 7f e3 1b 00 00 00 20 f9 0x0028 7f e3 1b 00 00 00 20 f9
0x0030 4d a7 bb 48 d6 0a 61 e5 0x0030 4d a7 bb 48 d6 0a 61 e5
0x0038 67 70 6a 65 87 d0 33 19 0x0038 67 70 6a 65 87 d0 33 19
0x0040 99 bb 9d 89 1a 08 24 2e 0x0040 99 bb 9d 89 1a 08 24 2e
0x0048 ad 84 54 3d f8 95 a3 06 0x0048 ad 84 54 3d f8 95 a3 06
0x0050 1f 1b 0a 00 00 00 42 05 0x0050 1f 1b 0a 00 00 00 42 05
0x0058 82 63 87 7f e3 03 0b 09 0x0058 82 63 87 7f e3 03 0b 09
0x0060 07 05 15 0a 0e 08 0c 02 0x0060 07 05 15 0a 0e 08 0c 02
0x0068 16 00 02 9b 03 02 1e 09 0x0068 16 00 02 9b 03 02 1e 09
0x0070 22 21 06 cb 18 6c 4f 06 0x0070 22 21 06 cb 18 6c 4f 06
0x0078 09 a6 97 e4 d5 2d fa 6c 0x0078 09 a6 97 e4 d5 2d fa 6c
0x0080 72 2b 0c 1f 1e 27 c1 8a 0x0080 72 2b 0c 1f 1e 27 c1 8a
0x0088 56 70 8f 65 25 ec 27 ba 0x0088 56 70 8f 65 25 ec 27 ba
0x0090 d9 ac c9 05 27 09 02 07 0x0090 d9 ac c9 05 27 09 02 07
0x0098 02 06 ff 00 00 00 4a 0x0098 02 06 ff 00 00 00 4a
]]></artwork></figure> ]]></artwork>
<t>The same data, broken out by octet and semantics, is:</t>
<t>The same data, broken out by octet and semantics, is:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 10 3e 2d 7d 22 7e c0 e6 salt 0x0000 10 3e 2d 7d 22 7e c0 e6 salt
0x0008 d7 ce 44 71 db 36 bf c9 0x0008 d7 ce 44 71 db 36 bf c9
0x0010 70 83 25 36 90 27 14 98 0x0010 70 83 25 36 90 27 14 98
0x0018 a7 ef 05 76 c0 7f aa e1 0x0018 a7 ef 05 76 c0 7f aa e1
[ pubkey begins ] [ pubkey begins ]
0x0020 9b v6 pubkey 0x0020 9b key packet
0x0021 00 00 00 2a pubkey length 0x0021 00 00 00 2a pubkey length
0x0025 06 pubkey version 0x0025 06 pubkey version
0x0026 63 87 creation time 0x0026 63 87 creation time
0x0028 7f e3 (2022-11-30T16:08:03Z) 0x0028 7f e3 (2022-11-30T16:08:03Z)
0x002a 1b key algo: Ed25519 0x002a 1b key algo: Ed25519
0x002b 00 00 00 20 key length 0x002b 00 00 00 20 key length
0x002f f9 Ed25519 public key 0x002f f9 Ed25519 public key
0x0030 4d a7 bb 48 d6 0a 61 e5 0x0030 4d a7 bb 48 d6 0a 61 e5
0x0038 67 70 6a 65 87 d0 33 19 0x0038 67 70 6a 65 87 d0 33 19
0x0040 99 bb 9d 89 1a 08 24 2e 0x0040 99 bb 9d 89 1a 08 24 2e
0x0048 ad 84 54 3d f8 95 a3 0x0048 ad 84 54 3d f8 95 a3
[ trailer begins ] [ trailer begins ]
0x004f 06 sig version 0x004f 06 sig version 6
0x0050 1f sig type: direct key signature 0x0050 1f sig type: Direct Key signature
0x0051 1b sig algo: Ed25519 0x0051 1b sig algo: Ed25519
0x0052 0a hash ago: SHA2-512 0x0052 0a hash ago: SHA2-512
0x0053 00 00 00 42 hashed subpackets length 0x0053 00 00 00 42 hashed subpackets length
0x0057 05 subpkt length 0x0057 05 subpkt length
0x0058 82 critical subpkt: Sig Creation Time 0x0058 82 critical subpkt: Sig Creation Time
0x0059 63 87 7f e3 Signature Creation Time 0x0059 63 87 7f e3 Signature Creation Time
0x005d 03 subpkt length 0x005d 03 subpkt length
0x005e 0b subpkt type: Pref. v1 SEIPD Ciphers 0x005e 0b subpkt type: Pref. v1 SEIPD Ciphers
0x005f 09 Ciphers: [AES256 AES128] 0x005f 09 Ciphers: [AES256 AES128]
0x0060 07 0x0060 07
skipping to change at line 6825 skipping to change at line 6829
0x0063 0a 0e Hashes: [SHA2-512 SHA3-512 0x0063 0a 0e Hashes: [SHA2-512 SHA3-512
0x0065 08 0c SHA2-256 SHA3-256] 0x0065 08 0c SHA2-256 SHA3-256]
0x0067 02 subpkt length 0x0067 02 subpkt length
0x0068 16 subpkt type: Pref. Compression 0x0068 16 subpkt type: Pref. Compression
0x0069 00 Compression: [none] 0x0069 00 Compression: [none]
0x006a 02 subpkt length 0x006a 02 subpkt length
0x006b 9b critical subpkt: Key Flags 0x006b 9b critical subpkt: Key Flags
0x006c 03 Key Flags: {certify, sign} 0x006c 03 Key Flags: {certify, sign}
0x006d 02 subpkt length 0x006d 02 subpkt length
0x006e 1e subpkt type: Features 0x006e 1e subpkt type: Features
0x006f 09 Features: {SEIPDv1, SEIPDv2} 0x006f 09 Features: {v1SEIPD, v2SEIPD}
0x0070 22 subpkt length 0x0070 22 subpkt length
0x0071 21 subpkt type: Issuer Fingerprint 0x0071 21 subpkt type: Issuer Fingerprint
0x0072 06 Fingerprint version 6 0x0072 06 Fingerprint version 6
0x0073 cb 18 6c 4f 06 Issuer Fingerprint 0x0073 cb 18 6c 4f 06 Fingerprint
0x0078 09 a6 97 e4 d5 2d fa 6c 0x0078 09 a6 97 e4 d5 2d fa 6c
0x0080 72 2b 0c 1f 1e 27 c1 8a 0x0080 72 2b 0c 1f 1e 27 c1 8a
0x0088 56 70 8f 65 25 ec 27 ba 0x0088 56 70 8f 65 25 ec 27 ba
0x0090 d9 ac c9 0x0090 d9 ac c9
0x0093 05 subpkt length 0x0093 05 subpkt length
0x0094 27 subpkt type: Pref. AEAD Ciphersuites 0x0094 27 subpkt type: Pref. AEAD Ciphersuites
0x0095 09 02 07 Ciphersuites: 0x0095 09 02 07 Ciphersuites:
0x0098 02 [ AES256-OCB, AES128-OCB ] 0x0098 02 [ AES256-OCB, AES128-OCB ]
0x0099 06 sig version 0x0099 06 sig version 6
0x009a ff sentinel octet 0x009a ff sentinel octet
0x009b 00 00 00 4a trailer length 0x009b 00 00 00 4a trailer length
]]></artwork></figure> ]]></artwork>
<t>The Subkey Binding signature in <xref target="v6-cert"/> is made ov
<t>The subkey binding signature in <xref target="v6-cert"/> is made over the fol er the following sequence of data:</t>
lowing sequence of data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 a6 e9 18 6d 9d 59 35 fc 0x0000 a6 e9 18 6d 9d 59 35 fc
0x0008 8f e5 63 14 cd b5 27 48 0x0008 8f e5 63 14 cd b5 27 48
0x0010 6a 5a 51 20 f9 b7 62 a2 0x0010 6a 5a 51 20 f9 b7 62 a2
0x0018 35 a7 29 f0 39 01 0a 56 0x0018 35 a7 29 f0 39 01 0a 56
0x0020 9b 00 00 00 2a 06 63 87 0x0020 9b 00 00 00 2a 06 63 87
0x0028 7f e3 1b 00 00 00 20 f9 0x0028 7f e3 1b 00 00 00 20 f9
0x0030 4d a7 bb 48 d6 0a 61 e5 0x0030 4d a7 bb 48 d6 0a 61 e5
0x0038 67 70 6a 65 87 d0 33 19 0x0038 67 70 6a 65 87 d0 33 19
0x0040 99 bb 9d 89 1a 08 24 2e 0x0040 99 bb 9d 89 1a 08 24 2e
0x0048 ad 84 54 3d f8 95 a3 9b 0x0048 ad 84 54 3d f8 95 a3 9b
skipping to change at line 6869 skipping to change at line 6871
0x0068 22 f8 f4 80 95 dd a7 84 0x0068 22 f8 f4 80 95 dd a7 84
0x0070 98 7f 2d 59 85 b1 2f ba 0x0070 98 7f 2d 59 85 b1 2f ba
0x0078 d1 6c af 5e 44 35 06 18 0x0078 d1 6c af 5e 44 35 06 18
0x0080 1b 0a 00 00 00 2c 05 82 0x0080 1b 0a 00 00 00 2c 05 82
0x0088 63 87 7f e3 02 9b 0c 22 0x0088 63 87 7f e3 02 9b 0c 22
0x0090 21 06 cb 18 6c 4f 06 09 0x0090 21 06 cb 18 6c 4f 06 09
0x0098 a6 97 e4 d5 2d fa 6c 72 0x0098 a6 97 e4 d5 2d fa 6c 72
0x00a0 2b 0c 1f 1e 27 c1 8a 56 0x00a0 2b 0c 1f 1e 27 c1 8a 56
0x00a8 70 8f 65 25 ec 27 ba d9 0x00a8 70 8f 65 25 ec 27 ba d9
0x00b0 ac c9 06 ff 00 00 00 34 0x00b0 ac c9 06 ff 00 00 00 34
]]></artwork></figure> ]]></artwork>
<t>The same data, broken out by octet and semantics, is:</t>
<t>The same data, broken out by octet and semantics, is:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 a6 e9 18 6d 9d 59 35 fc salt 0x0000 a6 e9 18 6d 9d 59 35 fc salt
0x0008 8f e5 63 14 cd b5 27 48 0x0008 8f e5 63 14 cd b5 27 48
0x0010 6a 5a 51 20 f9 b7 62 a2 0x0010 6a 5a 51 20 f9 b7 62 a2
0x0018 35 a7 29 f0 39 01 0a 56 0x0018 35 a7 29 f0 39 01 0a 56
[ primary pubkey begins ] [ primary pubkey begins ]
0x0020 9b v6 pubkey 0x0020 9b key packet
0x0021 00 00 00 2a pubkey length 0x0021 00 00 00 2a pubkey length
0x0025 06 pubkey version 0x0025 06 pubkey version
0x0026 63 87 creation time 0x0026 63 87 creation time
0x0028 7f e3 (2022-11-30T16:08:03Z) 0x0028 7f e3 (2022-11-30T16:08:03Z)
0x002a 1b key algo: Ed25519 0x002a 1b key algo: Ed25519
0x002b 00 00 00 20 key length 0x002b 00 00 00 20 key length
0x002f f9 Ed25519 public key 0x002f f9 Ed25519 public key
0x0030 4d a7 bb 48 d6 0a 61 e5 0x0030 4d a7 bb 48 d6 0a 61 e5
0x0038 67 70 6a 65 87 d0 33 19 0x0038 67 70 6a 65 87 d0 33 19
0x0040 99 bb 9d 89 1a 08 24 2e 0x0040 99 bb 9d 89 1a 08 24 2e
0x0048 ad 84 54 3d f8 95 a3 0x0048 ad 84 54 3d f8 95 a3
[ subkey pubkey begins ] [ subkey pubkey begins ]
0x004f 9b v6 key 0x004f 9b key packet
0x0050 00 00 00 2a pubkey length 0x0050 00 00 00 2a pubkey length
0x0054 06 pubkey version 0x0054 06 pubkey version
0x0055 63 87 7f creation time (2022-11-30T16:08:03Z) 0x0055 63 87 7f creation time (2022-11-30T16:08:03Z)
0x0058 e3 0x0058 e3
0x0059 19 key algo: X25519 0x0059 19 key algo: X25519
0x005a 00 00 00 20 key length 0x005a 00 00 00 20 key length
0x005e 86 93 X25519 public key 0x005e 86 93 X25519 public key
0x0060 24 83 67 f9 e5 01 5d b9 0x0060 24 83 67 f9 e5 01 5d b9
0x0068 22 f8 f4 80 95 dd a7 84 0x0068 22 f8 f4 80 95 dd a7 84
0x0070 98 7f 2d 59 85 b1 2f ba 0x0070 98 7f 2d 59 85 b1 2f ba
0x0078 d1 6c af 5e 44 35 0x0078 d1 6c af 5e 44 35
[ trailer begins ] [ trailer begins ]
0x007e 06 sig version 0x007e 06 sig version 6
0x007f 18 sig type: Subkey Binding sig 0x007f 18 sig type: Subkey Binding sig
0x0080 1b sig algo Ed25519 0x0080 1b sig algo Ed25519
0x0081 0a hash algo: SHA2-512 0x0081 0a hash algo: SHA2-512
0x0082 00 00 00 2c hashed subpackets length 0x0082 00 00 00 2c hashed subpackets length
0x0086 05 subpkt length 0x0086 05 subpkt length
0x0087 82 critical subpkt: Sig Creation Time 0x0087 82 critical subpkt: Sig Creation Time
0x0088 63 87 7f e3 Signature Creation Time 0x0088 63 87 7f e3 Signature Creation Time
0x008c 02 subpkt length 0x008c 02 subpkt length
0x008d 9b critical subpkt: Key Flags 0x008d 9b critical subpkt: Key Flags
0x008e 0c Key Flags: {EncComms, EncStorage} 0x008e 0c Key Flags: {EncComms, EncStorage}
0x008f 22 subpkt length 0x008f 22 subpkt length
0x0090 21 subpkt type: Issuer Fingerprint 0x0090 21 subpkt type: Issuer Fingerprint
0x0091 06 Fingerprint version 6 0x0091 06 Fingerprint version 6
0x0092 cb 18 6c 4f 06 09 Fingerprint 0x0092 cb 18 6c 4f 06 09 Fingerprint
0x0098 a6 97 e4 d5 2d fa 6c 72 0x0098 a6 97 e4 d5 2d fa 6c 72
0x00a0 2b 0c 1f 1e 27 c1 8a 56 0x00a0 2b 0c 1f 1e 27 c1 8a 56
0x00a8 70 8f 65 25 ec 27 ba d9 0x00a8 70 8f 65 25 ec 27 ba d9
0x00b0 ac c9 0x00b0 ac c9
0x00b2 06 sig version 0x00b2 06 sig version 6
0x00b3 ff sentinel octet 0x00b3 ff sentinel octet
0x00b4 00 00 00 34 trailer length 0x00b4 00 00 00 34 trailer length
]]></artwork></figure> ]]></artwork>
</section>
</section> </section>
</section> <section anchor="v6-key">
<section anchor="v6-key"><name>Sample v6 Secret Key (Transferable Secret Key)</n <name>Sample Version 6 Secret Key (Transferable Secret Key)</name>
ame> <t>Here is a Transferable Secret Key consisting of:</t>
<ul spacing="normal">
<t>Here is a Transferable Secret Key consisting of:</t> <li>
<t>A version 6 Ed25519 Secret Key packet</t>
<t><list style="symbols"> </li>
<t>A v6 Ed25519 Secret-Key packet</t> <li>
<t>A v6 direct key self-signature</t> <t>A version 6 Direct Key self-signature</t>
<t>A v6 X25519 Secret-Subkey packet</t> </li>
<t>A v6 subkey binding signature</t> <li>
</list></t> <t>A version 6 X25519 Secret Subkey packet</t>
</li>
<figure><sourcecode type="application/pgp-keys" name="v6-minimal-secret.key"><![ <li>
CDATA[ <t>A version 6 Subkey Binding signature</t>
</li>
</ul>
<sourcecode type="application/pgp-keys" name="v6-minimal-secret.key"><![
CDATA[
-----BEGIN PGP PRIVATE KEY BLOCK----- -----BEGIN PGP PRIVATE KEY BLOCK-----
xUsGY4d/4xsAAAAg+U2nu0jWCmHlZ3BqZYfQMxmZu52JGggkLq2EVD34laMAGXKB xUsGY4d/4xsAAAAg+U2nu0jWCmHlZ3BqZYfQMxmZu52JGggkLq2EVD34laMAGXKB
exK+cH6NX1hs5hNhIB00TrJmosgv3mg1ditlsLfCsQYfGwoAAABCBYJjh3/jAwsJ exK+cH6NX1hs5hNhIB00TrJmosgv3mg1ditlsLfCsQYfGwoAAABCBYJjh3/jAwsJ
BwUVCg4IDAIWAAKbAwIeCSIhBssYbE8GCaaX5NUt+mxyKwwfHifBilZwj2Ul7Ce6 BwUVCg4IDAIWAAKbAwIeCSIhBssYbE8GCaaX5NUt+mxyKwwfHifBilZwj2Ul7Ce6
2azJBScJAgcCAAAAAK0oIBA+LX0ifsDm185Ecds2v8lwgyU2kCcUmKfvBXbAf6rh 2azJBScJAgcCAAAAAK0oIBA+LX0ifsDm185Ecds2v8lwgyU2kCcUmKfvBXbAf6rh
RYWzuQOwEn7E/aLwIwRaLsdry0+VcallHhSu4RN6HWaEQsiPlR4zxP/TP7mhfVEe RYWzuQOwEn7E/aLwIwRaLsdry0+VcallHhSu4RN6HWaEQsiPlR4zxP/TP7mhfVEe
7XWPxtnMUMtf15OyA51YBMdLBmOHf+MZAAAAIIaTJINn+eUBXbki+PSAld2nhJh/ 7XWPxtnMUMtf15OyA51YBMdLBmOHf+MZAAAAIIaTJINn+eUBXbki+PSAld2nhJh/
LVmFsS+60WyvXkQ1AE1gCk95TUR3XFeibg/u/tVY6a//1q0NWC1X+yui3O24wpsG LVmFsS+60WyvXkQ1AE1gCk95TUR3XFeibg/u/tVY6a//1q0NWC1X+yui3O24wpsG
GBsKAAAALAWCY4d/4wKbDCIhBssYbE8GCaaX5NUt+mxyKwwfHifBilZwj2Ul7Ce6 GBsKAAAALAWCY4d/4wKbDCIhBssYbE8GCaaX5NUt+mxyKwwfHifBilZwj2Ul7Ce6
2azJAAAAAAQBIKbpGG2dWTX8j+VjFM21J0hqWlEg+bdiojWnKfA5AQpWUWtnNwDE 2azJAAAAAAQBIKbpGG2dWTX8j+VjFM21J0hqWlEg+bdiojWnKfA5AQpWUWtnNwDE
M0g12vYxoWM8Y81W+bHBw805I8kWVkXU6vFOi+HWvv/ira7ofJu16NnoUkhclkUr M0g12vYxoWM8Y81W+bHBw805I8kWVkXU6vFOi+HWvv/ira7ofJu16NnoUkhclkUr
k0mXubZvyl4GBg== k0mXubZvyl4GBg==
-----END PGP PRIVATE KEY BLOCK----- -----END PGP PRIVATE KEY BLOCK-----
]]></sourcecode></figure> ]]></sourcecode>
<t>The corresponding Transferable Public Key can be found in <xref targe
<t>The corresponding Transferable Public Key can be found in <xref target="v6-ce t="v6-cert"/>.</t>
rt"/>.</t> </section>
<section anchor="v6-locked-key">
</section> <name>Sample Locked Version 6 Secret Key (Transferable Secret Key)</name
<section anchor="v6-locked-key"><name>Sample locked v6 Secret Key (Transferable >
Secret Key)</name> <t>Here is the same secret key as in <xref target="v6-key"/>, but the se
cret key material is locked with a passphrase using AEAD and Argon2.</t>
<t>Here is the same secret key as in <xref target="v6-key"/>, but the secret key <t>The passphrase is the ASCII string:</t>
material is locked with a passphrase using AEAD and Argon2.</t> <artwork><![CDATA[
<t>The passphrase is the ASCII string:</t>
<figure><artwork><![CDATA[
correct horse battery staple correct horse battery staple
]]></artwork></figure> ]]></artwork>
<sourcecode type="application/pgp-keys" name="v6-minimal-secret-locked.k
<figure><sourcecode type="application/pgp-keys" name="v6-minimal-secret-locked.k ey"><![CDATA[
ey"><![CDATA[
-----BEGIN PGP PRIVATE KEY BLOCK----- -----BEGIN PGP PRIVATE KEY BLOCK-----
xYIGY4d/4xsAAAAg+U2nu0jWCmHlZ3BqZYfQMxmZu52JGggkLq2EVD34laP9JgkC xYIGY4d/4xsAAAAg+U2nu0jWCmHlZ3BqZYfQMxmZu52JGggkLq2EVD34laP9JgkC
FARdb9ccngltHraRe25uHuyuAQQVtKipJ0+r5jL4dacGWSAheCWPpITYiyfyIOPS FARdb9ccngltHraRe25uHuyuAQQVtKipJ0+r5jL4dacGWSAheCWPpITYiyfyIOPS
3gIDyg8f7strd1OB4+LZsUhcIjOMpVHgmiY/IutJkulneoBYwrEGHxsKAAAAQgWC 3gIDyg8f7strd1OB4+LZsUhcIjOMpVHgmiY/IutJkulneoBYwrEGHxsKAAAAQgWC
Y4d/4wMLCQcFFQoOCAwCFgACmwMCHgkiIQbLGGxPBgmml+TVLfpscisMHx4nwYpW Y4d/4wMLCQcFFQoOCAwCFgACmwMCHgkiIQbLGGxPBgmml+TVLfpscisMHx4nwYpW
cI9lJewnutmsyQUnCQIHAgAAAACtKCAQPi19In7A5tfORHHbNr/JcIMlNpAnFJin cI9lJewnutmsyQUnCQIHAgAAAACtKCAQPi19In7A5tfORHHbNr/JcIMlNpAnFJin
7wV2wH+q4UWFs7kDsBJ+xP2i8CMEWi7Ha8tPlXGpZR4UruETeh1mhELIj5UeM8T/ 7wV2wH+q4UWFs7kDsBJ+xP2i8CMEWi7Ha8tPlXGpZR4UruETeh1mhELIj5UeM8T/
0z+5oX1RHu11j8bZzFDLX9eTsgOdWATHggZjh3/jGQAAACCGkySDZ/nlAV25Ivj0 0z+5oX1RHu11j8bZzFDLX9eTsgOdWATHggZjh3/jGQAAACCGkySDZ/nlAV25Ivj0
gJXdp4SYfy1ZhbEvutFsr15ENf0mCQIUBA5hhGgp2oaavg6mFUXcFMwBBBUuE8qf gJXdp4SYfy1ZhbEvutFsr15ENf0mCQIUBA5hhGgp2oaavg6mFUXcFMwBBBUuE8qf
9Ock+xwusd+GAglBr5LVyr/lup3xxQvHXFSjjA2haXfoN6xUGRdDEHI6+uevKjVR 9Ock+xwusd+GAglBr5LVyr/lup3xxQvHXFSjjA2haXfoN6xUGRdDEHI6+uevKjVR
v5oAxgu7eJpaXNjCmwYYGwoAAAAsBYJjh3/jApsMIiEGyxhsTwYJppfk1S36bHIr v5oAxgu7eJpaXNjCmwYYGwoAAAAsBYJjh3/jApsMIiEGyxhsTwYJppfk1S36bHIr
DB8eJ8GKVnCPZSXsJ7rZrMkAAAAABAEgpukYbZ1ZNfyP5WMUzbUnSGpaUSD5t2Ki DB8eJ8GKVnCPZSXsJ7rZrMkAAAAABAEgpukYbZ1ZNfyP5WMUzbUnSGpaUSD5t2Ki
Nacp8DkBClZRa2c3AMQzSDXa9jGhYzxjzVb5scHDzTkjyRZWRdTq8U6L4da+/+Kt Nacp8DkBClZRa2c3AMQzSDXa9jGhYzxjzVb5scHDzTkjyRZWRdTq8U6L4da+/+Kt
ruh8m7Xo2ehSSFyWRSuTSZe5tm/KXgYG ruh8m7Xo2ehSSFyWRSuTSZe5tm/KXgYG
-----END PGP PRIVATE KEY BLOCK----- -----END PGP PRIVATE KEY BLOCK-----
]]></sourcecode></figure> ]]></sourcecode>
<section anchor="intermediate-data-for-locked-primary-key">
<section anchor="intermediate-data-for-locked-primary-key"><name>Intermediate Da <name>Intermediate Data for Locked Primary Key</name>
ta for Locked Primary Key</name> <t>The S2K-derived material for the primary key is:</t>
<artwork><![CDATA[
<t>The S2K-derived material for the primary key is:</t>
<figure><artwork><![CDATA[
832bd2662a5c2b251ee3fc82aec349a766ca539015880133002e5a21960b3bcf 832bd2662a5c2b251ee3fc82aec349a766ca539015880133002e5a21960b3bcf
]]></artwork></figure> ]]></artwork>
<t>After HKDF, the symmetric key used for AEAD encryption of the prima
<t>After HKDF, the symmetric key used for AEAD encryption of the primary key is: ry key is:</t>
</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
9e37cb26787f37e18db172795c4c297550d39ac82511d9af4c8706db6a77fd51 9e37cb26787f37e18db172795c4c297550d39ac82511d9af4c8706db6a77fd51
]]></artwork></figure> ]]></artwork>
<t>The additional data for AEAD for the primary key is:</t>
<t>The additional data for AEAD for the primary key is:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
c50663877fe31b00000020f94da7bb48d60a61e567706a6587d0331999bb9d89 c50663877fe31b00000020f94da7bb48d60a61e567706a6587d0331999bb9d89
1a08242ead84543df895a3 1a08242ead84543df895a3
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="intermediate-data-for-locked-subkey">
<section anchor="intermediate-data-for-locked-subkey"><name>Intermediate Data fo <name>Intermediate Data for Locked Subkey</name>
r Locked Subkey</name> <t>The S2K-derived key material for the subkey is:</t>
<artwork><![CDATA[
<t>The S2K-derived key material for the subkey is:</t>
<figure><artwork><![CDATA[
f74a6ce873a089ef13a3da9ac059777bb22340d15eaa6c9dc0f8ef09035c67cd f74a6ce873a089ef13a3da9ac059777bb22340d15eaa6c9dc0f8ef09035c67cd
]]></artwork></figure> ]]></artwork>
<t>After HKDF, the symmetric key used for AEAD encryption of the subke
<t>After HKDF, the symmetric key used for AEAD encryption of the subkey is:</t> y is:</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
3c60cb63285f62f4c3de49835786f011cf6f4c069f61232cd7013ff5fd31e603 3c60cb63285f62f4c3de49835786f011cf6f4c069f61232cd7013ff5fd31e603
]]></artwork></figure> ]]></artwork>
<t>The additional data for AEAD for the subkey is:</t>
<t>The additional data for AEAD for the subkey is:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
c70663877fe319000000208693248367f9e5015db922f8f48095dda784987f2d c70663877fe319000000208693248367f9e5015db922f8f48095dda784987f2d
5985b12fbad16caf5e4435 5985b12fbad16caf5e4435
]]></artwork></figure> ]]></artwork>
</section>
</section> </section>
</section> <section anchor="sample-csf-message">
<section anchor="sample-csf-message"><name>Sample Cleartext Signed Message</name <name>Sample Cleartext Signed Message</name>
> <t>Here is a signed message that uses the Cleartext Signature Framework
(<xref target="cleartext-signature"/>). It can be verified with the certificate
<t>Here is a signed message that uses the cleartext signature framework (<xref t from <xref target="v6-cert"/>.</t>
arget="cleartext-signature"/>). <t>Note that this message makes use of dash-escaping (<xref target="dash
It can be verified with the certificate from (<xref target="v6-cert"/>).</t> -escaping"/>) due to its contents.</t>
<sourcecode type="text/plain" name="cleartext-signed-message.txt"><![CDA
<t>Note that this message makes use of dash-escaping (<xref target="dash-escapin TA[
g"/>) due to its contents.</t>
<figure><sourcecode type="text/plain" name="cleartext-signed-message.txt"><![CDA
TA[
-----BEGIN PGP SIGNED MESSAGE----- -----BEGIN PGP SIGNED MESSAGE-----
What we need from the grocery store: What we need from the grocery store:
- - tofu - - tofu
- - vegetables - - vegetables
- - noodles - - noodles
-----BEGIN PGP SIGNATURE----- -----BEGIN PGP SIGNATURE-----
wpgGARsKAAAAKQWCY5ijYyIhBssYbE8GCaaX5NUt+mxyKwwfHifBilZwj2Ul7Ce6 wpgGARsKAAAAKQWCY5ijYyIhBssYbE8GCaaX5NUt+mxyKwwfHifBilZwj2Ul7Ce6
2azJAAAAAGk2IHZJX1AhiJD39eLuPBgiUU9wUA9VHYblySHkBONKU/usJ9BvuAqo 2azJAAAAAGk2IHZJX1AhiJD39eLuPBgiUU9wUA9VHYblySHkBONKU/usJ9BvuAqo
/FvLFuGWMbKAdA+epq7V4HOtAPlBWmU8QOd6aud+aSunHQaaEJ+iTFjP2OMW0KBr /FvLFuGWMbKAdA+epq7V4HOtAPlBWmU8QOd6aud+aSunHQaaEJ+iTFjP2OMW0KBr
NK2ay45cX1IVAQ== NK2ay45cX1IVAQ==
-----END PGP SIGNATURE----- -----END PGP SIGNATURE-----
]]></sourcecode></figure> ]]></sourcecode>
<t>The Signature packet here is:</t>
<t>The signature packet here is:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 c2 packet type: Signature 0x0000 c2 packet type: Signature
0x0001 98 packet length 0x0001 98 packet length
0x0002 06 signature version 6 0x0002 06 sig version 6
0x0003 01 signature type: canonical text 0x0003 01 sig type: Canonical Text
0x0004 1b pubkey algorithm: Ed25519 0x0004 1b pubkey algorithm: Ed25519
0x0005 0a hash algorithm used: SHA2-512 0x0005 0a hash algorithm used: SHA2-512
0x0006 00 00 hashed subpackets length: 41 0x0006 00 00 hashed subpackets length: 41
0x0008 00 29 0x0008 00 29
0x000a 05 subpkt length 0x000a 05 subpkt length
0x000b 82 critical subpkt: Sig Creation Time 0x000b 82 critical subpkt: Sig Creation Time
0x000c 63 98 a3 63 (2022-12-13T16:08:03Z) 0x000c 63 98 a3 63 (2022-12-13T16:08:03Z)
0x0010 22 subpkt length 0x0010 22 subpkt length
0x0011 21 subpkt type: issuer fingerprint 0x0011 21 subpkt type: Issuer Fingerprint
0x0012 06 key version 0x0012 06 Fingerprint version 6
0x0013 cb 18 6c 4f 06 v6 fingerprint 0x0013 cb 18 6c 4f 06 Fingerprint
0x001a 09 a6 97 e4 d5 2d fa 6c 0x001a 09 a6 97 e4 d5 2d fa 6c
0x0020 72 2b 0c 1f 1e 27 c1 8a 0x0020 72 2b 0c 1f 1e 27 c1 8a
0x0028 56 70 8f 65 25 ec 27 ba 0x0028 56 70 8f 65 25 ec 27 ba
0x0030 d9 ac c9 0x0030 d9 ac c9
0x0033 00 00 00 00 unhashed subpackets length: 0 0x0033 00 00 00 00 unhashed subpackets length: 0
0x0037 69 left 16 bits of signed hash 0x0037 69 left 16 bits of signed hash
0x0038 36 0x0038 36
0x0039 20 salt length 0x0039 20 salt length
0x003a 76 49 5f 50 21 88 salt 0x003a 76 49 5f 50 21 88 salt
0x0040 90 f7 f5 e2 ee 3c 18 22 0x0040 90 f7 f5 e2 ee 3c 18 22
skipping to change at line 7101 skipping to change at line 7083
0x0058 fb ac 0x0058 fb ac
0x005a 27 d0 6f b8 0a a8 Ed25519 signature 0x005a 27 d0 6f b8 0a a8 Ed25519 signature
0x0060 fc 5b cb 16 e1 96 31 b2 0x0060 fc 5b cb 16 e1 96 31 b2
0x0068 80 74 0f 9e a6 ae d5 e0 0x0068 80 74 0f 9e a6 ae d5 e0
0x0070 73 ad 00 f9 41 5a 65 3c 0x0070 73 ad 00 f9 41 5a 65 3c
0x0078 40 e7 7a 6a e7 7e 69 2b 0x0078 40 e7 7a 6a e7 7e 69 2b
0x0080 a7 1d 06 9a 10 9f a2 4c 0x0080 a7 1d 06 9a 10 9f a2 4c
0x0088 58 cf d8 e3 16 d0 a0 6b 0x0088 58 cf d8 e3 16 d0 a0 6b
0x0090 34 ad 9a cb 8e 5c 5f 52 0x0090 34 ad 9a cb 8e 5c 5f 52
0x0098 15 01 0x0098 15 01
]]></artwork></figure> ]]></artwork>
<t>The signature is made over the following data:</t>
<t>The signature is made over the following data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 76 49 5f 50 21 88 90 f7 0x0000 76 49 5f 50 21 88 90 f7
0x0008 f5 e2 ee 3c 18 22 51 4f 0x0008 f5 e2 ee 3c 18 22 51 4f
0x0010 70 50 0f 55 1d 86 e5 c9 0x0010 70 50 0f 55 1d 86 e5 c9
0x0018 21 e4 04 e3 4a 53 fb ac 0x0018 21 e4 04 e3 4a 53 fb ac
0x0020 57 68 61 74 20 77 65 20 0x0020 57 68 61 74 20 77 65 20
0x0028 6e 65 65 64 20 66 72 6f 0x0028 6e 65 65 64 20 66 72 6f
0x0030 6d 20 74 68 65 20 67 72 0x0030 6d 20 74 68 65 20 67 72
0x0038 6f 63 65 72 79 20 73 74 0x0038 6f 63 65 72 79 20 73 74
0x0040 6f 72 65 3a 0d 0a 0d 0a 0x0040 6f 72 65 3a 0d 0a 0d 0a
0x0048 2d 20 74 6f 66 75 0d 0a 0x0048 2d 20 74 6f 66 75 0d 0a
0x0050 2d 20 76 65 67 65 74 61 0x0050 2d 20 76 65 67 65 74 61
0x0058 62 6c 65 73 0d 0a 2d 20 0x0058 62 6c 65 73 0d 0a 2d 20
0x0060 6e 6f 6f 64 6c 65 73 0d 0x0060 6e 6f 6f 64 6c 65 73 0d
0x0068 0a 06 01 1b 0a 00 00 00 0x0068 0a 06 01 1b 0a 00 00 00
0x0070 29 05 82 63 98 a3 63 22 0x0070 29 05 82 63 98 a3 63 22
0x0078 21 06 cb 18 6c 4f 06 09 0x0078 21 06 cb 18 6c 4f 06 09
0x0080 a6 97 e4 d5 2d fa 6c 72 0x0080 a6 97 e4 d5 2d fa 6c 72
0x0088 2b 0c 1f 1e 27 c1 8a 56 0x0088 2b 0c 1f 1e 27 c1 8a 56
0x0090 70 8f 65 25 ec 27 ba d9 0x0090 70 8f 65 25 ec 27 ba d9
0x0098 ac c9 06 ff 00 00 00 31 0x0098 ac c9 06 ff 00 00 00 31
]]></artwork></figure> ]]></artwork>
<t>The same data, broken out by octet and semantics, is:</t>
<t>The same data, broken out by octet and semantics, is:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 76 49 5f 50 21 88 90 f7 salt 0x0000 76 49 5f 50 21 88 90 f7 salt
0x0008 f5 e2 ee 3c 18 22 51 4f 0x0008 f5 e2 ee 3c 18 22 51 4f
0x0010 70 50 0f 55 1d 86 e5 c9 0x0010 70 50 0f 55 1d 86 e5 c9
0x0018 21 e4 04 e3 4a 53 fb ac 0x0018 21 e4 04 e3 4a 53 fb ac
[ message begins ] [ message begins ]
0x0020 57 68 61 74 20 77 65 20 canonicalized message 0x0020 57 68 61 74 20 77 65 20 canonicalized message
0x0028 6e 65 65 64 20 66 72 6f 0x0028 6e 65 65 64 20 66 72 6f
0x0030 6d 20 74 68 65 20 67 72 0x0030 6d 20 74 68 65 20 67 72
0x0038 6f 63 65 72 79 20 73 74 0x0038 6f 63 65 72 79 20 73 74
0x0040 6f 72 65 3a 0d 0a 0d 0a 0x0040 6f 72 65 3a 0d 0a 0d 0a
0x0048 2d 20 74 6f 66 75 0d 0a 0x0048 2d 20 74 6f 66 75 0d 0a
0x0050 2d 20 76 65 67 65 74 61 0x0050 2d 20 76 65 67 65 74 61
0x0058 62 6c 65 73 0d 0a 2d 20 0x0058 62 6c 65 73 0d 0a 2d 20
0x0060 6e 6f 6f 64 6c 65 73 0d 0x0060 6e 6f 6f 64 6c 65 73 0d
0x0068 0a 0x0068 0a
[ trailer begins ] [ trailer begins ]
0x0069 06 sig version 0x0069 06 sig version 6
0x006a 01 sigtype: canonical text 0x006a 01 sig type: Canonical Text
0x006b 1b pubkey algorithm: Ed25519 0x006b 1b pubkey algorithm: Ed25519
0x006c 0a hash algorithm: SHA2-512 0x006c 0a hash algorithm: SHA2-512
0x006d 00 00 00 hashed subpackets length 0x006d 00 00 00 hashed subpackets length
0x0070 29 0x0070 29
0x0071 05 subpacket length 0x0071 05 subpacket length
0x0072 82 critical subpkt: Sig Creation Time 0x0072 82 critical subpkt: Sig Creation Time
0x0073 63 98 a3 63 (2022-12-13T16:08:03Z) 0x0073 63 98 a3 63 (2022-12-13T16:08:03Z)
0x0077 22 subpkt length 0x0077 22 subpkt length
0x0078 21 subpkt type: issuer fingerprint 0x0078 21 subpkt type: Issuer Fingerprint
0x0079 06 key version 0x0079 06 Fingerprint version 6
0x007a cb 18 6c 4f 06 09 v6 fingerprint 0x007a cb 18 6c 4f 06 09 Fingerprint
0x0080 a6 97 e4 d5 2d fa 6c 72 0x0080 a6 97 e4 d5 2d fa 6c 72
0x0088 2b 0c 1f 1e 27 c1 8a 56 0x0088 2b 0c 1f 1e 27 c1 8a 56
0x0090 70 8f 65 25 ec 27 ba d9 0x0090 70 8f 65 25 ec 27 ba d9
0x0098 ac c9 0x0098 ac c9
0x009a 06 sig version 0x009a 06 sig version 6
0x009b ff sentinel octet 0x009b ff sentinel octet
0x009c 00 00 00 31 trailer length 0x009c 00 00 00 31 trailer length
]]></artwork></figure> ]]></artwork>
<t>The calculated SHA2-512 hash digest over this data is:</t>
<t>The calculated SHA2-512 hash digest over this data is:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
69365bf44a97af1f0844f1f6ab83fdf6b36f26692efaa621a8aac91c4e29ea07 69365bf44a97af1f0844f1f6ab83fdf6b36f26692efaa621a8aac91c4e29ea07
e894cabc6e2f20eedfce6c03b89141a2cc7cbe245e6e7a5654addbec5000b89b e894cabc6e2f20eedfce6c03b89141a2cc7cbe245e6e7a5654addbec5000b89b
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="sample-inline-signed-message">
<section anchor="sample-inline-signed-message"><name>Sample inline-signed messag <name>Sample Inline-Signed Message</name>
e</name> <t>This is the same message and signature as in <xref target="sample-csf
-message"/> but as an inline-signed message. The hashed data is exactly the same
<t>This is the same message and signature as in <xref target="sample-csf-message , and all intermediate values and annotated hex dumps are also applicable.</t>
"/>, but as inline-signed message. <sourcecode type="text/plain" name="inline-signed-message.pgp"><![CDATA[
The hashed data is exactly the same, and all intermediate values and annotated h
ex dumps are also applicable.</t>
<figure><sourcecode type="text/plain" name="inline-signed-message.pgp"><![CDATA[
-----BEGIN PGP MESSAGE----- -----BEGIN PGP MESSAGE-----
xEYGAQobIHZJX1AhiJD39eLuPBgiUU9wUA9VHYblySHkBONKU/usyxhsTwYJppfk xEYGAQobIHZJX1AhiJD39eLuPBgiUU9wUA9VHYblySHkBONKU/usyxhsTwYJppfk
1S36bHIrDB8eJ8GKVnCPZSXsJ7rZrMkBy0p1AAAAAABXaGF0IHdlIG5lZWQgZnJv 1S36bHIrDB8eJ8GKVnCPZSXsJ7rZrMkBy0p1AAAAAABXaGF0IHdlIG5lZWQgZnJv
bSB0aGUgZ3JvY2VyeSBzdG9yZToKCi0gdG9mdQotIHZlZ2V0YWJsZXMKLSBub29k bSB0aGUgZ3JvY2VyeSBzdG9yZToKCi0gdG9mdQotIHZlZ2V0YWJsZXMKLSBub29k
bGVzCsKYBgEbCgAAACkFgmOYo2MiIQbLGGxPBgmml+TVLfpscisMHx4nwYpWcI9l bGVzCsKYBgEbCgAAACkFgmOYo2MiIQbLGGxPBgmml+TVLfpscisMHx4nwYpWcI9l
JewnutmsyQAAAABpNiB2SV9QIYiQ9/Xi7jwYIlFPcFAPVR2G5ckh5ATjSlP7rCfQ JewnutmsyQAAAABpNiB2SV9QIYiQ9/Xi7jwYIlFPcFAPVR2G5ckh5ATjSlP7rCfQ
b7gKqPxbyxbhljGygHQPnqau1eBzrQD5QVplPEDnemrnfmkrpx0GmhCfokxYz9jj b7gKqPxbyxbhljGygHQPnqau1eBzrQD5QVplPEDnemrnfmkrpx0GmhCfokxYz9jj
FtCgazStmsuOXF9SFQE= FtCgazStmsuOXF9SFQE=
-----END PGP MESSAGE----- -----END PGP MESSAGE-----
]]></sourcecode></figure> ]]></sourcecode>
</section>
</section> <section anchor="sample-x25519-aead-ocb-encryption-and-decryption">
<section anchor="sample-x25519-aead-ocb-encryption-and-decryption"><name>Sample <name>Sample X25519-AEAD-OCB Encryption and Decryption</name>
X25519-AEAD-OCB encryption and decryption</name> <t>This example encrypts the cleartext string <tt>Hello, world!</tt> for
the sample cert (see <xref target="v6-cert"/>), using AES-128 with AEAD-OCB enc
<t>This example encrypts the cleartext string <spanx style="verb">Hello, world!< ryption.</t>
/spanx> for the sample cert (see <xref target="v6-cert"/>), using AES-128 with A <section anchor="sample-public-key-encrypted-session-key-packet-v6">
EAD-OCB encryption.</t> <name>Sample Version 6 Public Key Encrypted Session Key Packet</name>
<t>This packet contains the following series of octets:</t>
<section anchor="sample-public-key-encrypted-session-key-packet-v6"><name>Sample <artwork name="v6pkesk-x25519.hexdump"><![CDATA[
public-key encrypted session key packet (v6)</name>
<t>This packet contains the following series of octets:</t>
<figure><artwork name="v6pkesk-x25519.hexdump"><![CDATA[
0x0000 c1 5d 06 21 06 12 c8 3f 0x0000 c1 5d 06 21 06 12 c8 3f
0x0008 1e 70 6f 63 08 fe 15 1a 0x0008 1e 70 6f 63 08 fe 15 1a
0x0010 41 77 43 a1 f0 33 79 0e 0x0010 41 77 43 a1 f0 33 79 0e
0x0018 93 e9 97 84 88 d1 db 37 0x0018 93 e9 97 84 88 d1 db 37
0x0020 8d a9 93 08 85 19 87 cf 0x0020 8d a9 93 08 85 19 87 cf
0x0028 18 d5 f1 b5 3f 81 7c ce 0x0028 18 d5 f1 b5 3f 81 7c ce
0x0030 5a 00 4c f3 93 cc 89 58 0x0030 5a 00 4c f3 93 cc 89 58
0x0038 bd dc 06 5f 25 f8 4a f5 0x0038 bd dc 06 5f 25 f8 4a f5
0x0040 09 b1 7d d3 67 64 18 de 0x0040 09 b1 7d d3 67 64 18 de
0x0048 a3 55 43 79 56 61 79 01 0x0048 a3 55 43 79 56 61 79 01
0x0050 e0 69 57 fb ca 8a 6a 47 0x0050 e0 69 57 fb ca 8a 6a 47
0x0058 a5 b5 15 3e 8d 3a b7 0x0058 a5 b5 15 3e 8d 3a b7
]]></artwork></figure> ]]></artwork>
<t>The same data, broken out by octet and semantics, is:</t>
<t>The same data, broken out by octet and semantics:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 c1 packet type: PKESK 0x0000 c1 packet type: PKESK
0x0001 5d packet length 0x0001 5d packet length
0x0002 06 PKESK version 6 0x0002 06 v6 PKESK
0x0003 21 length of fingerprint 0x0003 21 length of fingerprint
0x0004 06 Key version 6 0x0004 06 Key version 6
0x0005 12 c8 3f Key fingerprint 0x0005 12 c8 3f Key fingerprint
0x0008 1e 70 6f 63 08 fe 15 1a 0x0008 1e 70 6f 63 08 fe 15 1a
0x0010 41 77 43 a1 f0 33 79 0e 0x0010 41 77 43 a1 f0 33 79 0e
0x0018 93 e9 97 84 88 d1 db 37 0x0018 93 e9 97 84 88 d1 db 37
0x0020 8d a9 93 08 85 0x0020 8d a9 93 08 85
0x0025 19 algorithm: X25519 0x0025 19 algorithm: X25519
0x0026 87 cf Ephemeral key 0x0026 87 cf Ephemeral key
0x0028 18 d5 f1 b5 3f 81 7c ce 0x0028 18 d5 f1 b5 3f 81 7c ce
0x0030 5a 00 4c f3 93 cc 89 58 0x0030 5a 00 4c f3 93 cc 89 58
0x0038 bd dc 06 5f 25 f8 4a f5 0x0038 bd dc 06 5f 25 f8 4a f5
0x0040 09 b1 7d d3 67 64 0x0040 09 b1 7d d3 67 64
0x0046 18 ESK length 0x0046 18 ESK length
0x0047 de ESK 0x0047 de ESK
0x0048 a3 55 43 79 56 61 79 01 0x0048 a3 55 43 79 56 61 79 01
0x0050 e0 69 57 fb ca 8a 6a 47 0x0050 e0 69 57 fb ca 8a 6a 47
0x0058 a5 b5 15 3e 8d 3a b7 0x0058 a5 b5 15 3e 8d 3a b7
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="x25519-encryptiondecryption-of-the-session-key">
<section anchor="x25519-encryptiondecryption-of-the-session-key"><name>X25519 en <name>X25519 Encryption/Decryption of the Session Key</name>
cryption/decryption of the session key</name> <t>Ephemeral key:</t>
<artwork><![CDATA[
<t>Ephemeral key:</t>
<figure><artwork><![CDATA[
87 cf 18 d5 f1 b5 3f 81 7c ce 5a 00 4c f3 93 cc 87 cf 18 d5 f1 b5 3f 81 7c ce 5a 00 4c f3 93 cc
89 58 bd dc 06 5f 25 f8 4a f5 09 b1 7d d3 67 64 89 58 bd dc 06 5f 25 f8 4a f5 09 b1 7d d3 67 64
]]></artwork></figure> ]]></artwork>
<t>This ephemeral key is derived from the following ephemeral secret k
<t>This ephemeral key is derived from the following ephemeral secret key materia ey material, which is never placed on the wire:</t>
l, which is never placed on the wire:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
af 1e 43 c0 d1 23 ef e8 93 a7 d4 d3 90 f3 a7 61 af 1e 43 c0 d1 23 ef e8 93 a7 d4 d3 90 f3 a7 61
e3 fa c3 3d fc 7f 3e da a8 30 c9 01 13 52 c7 79 e3 fa c3 3d fc 7f 3e da a8 30 c9 01 13 52 c7 79
]]></artwork></figure> ]]></artwork>
<t>Public key from the target certificate (see <xref target="v6-cert"/
<t>Public key from target certificate (see <xref target="v6-cert"/>):</t> >):</t>
<artwork><![CDATA[
<figure><artwork><![CDATA[
86 93 24 83 67 f9 e5 01 5d b9 22 f8 f4 80 95 dd 86 93 24 83 67 f9 e5 01 5d b9 22 f8 f4 80 95 dd
a7 84 98 7f 2d 59 85 b1 2f ba d1 6c af 5e 44 35 a7 84 98 7f 2d 59 85 b1 2f ba d1 6c af 5e 44 35
]]></artwork></figure> ]]></artwork>
<t>The corresponding long-lived X25519 private key material (see <xref
<t>The corresponding long-lived X25519 private key material (see <xref target="v target="v6-key"/>):</t>
6-key"/>):</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
4d 60 0a 4f 79 4d 44 77 5c 57 a2 6e 0f ee fe d5 4d 60 0a 4f 79 4d 44 77 5c 57 a2 6e 0f ee fe d5
58 e9 af ff d6 ad 0d 58 2d 57 fb 2b a2 dc ed b8 58 e9 af ff d6 ad 0d 58 2d 57 fb 2b a2 dc ed b8
]]></artwork></figure> ]]></artwork>
<t>Shared point:</t>
<t>Shared point:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
67 e3 0e 69 cd c7 ba b2 a2 68 0d 78 ac a4 6a 2f 67 e3 0e 69 cd c7 ba b2 a2 68 0d 78 ac a4 6a 2f
8b 6e 2a e4 4d 39 8b dc 6f 92 c5 ad 4a 49 25 14 8b 6e 2a e4 4d 39 8b dc 6f 92 c5 ad 4a 49 25 14
]]></artwork></figure> ]]></artwork>
<t>HKDF output:</t>
<t>HKDF output:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
f6 6d ad cf f6 45 92 23 9b 25 45 39 b6 4f f6 07 f6 6d ad cf f6 45 92 23 9b 25 45 39 b6 4f f6 07
]]></artwork></figure> ]]></artwork>
<t>Decrypted session key:</t>
<t>Decrypted session key:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
dd 70 8f 6f a1 ed 65 11 4d 68 d2 34 3e 7c 2f 1d dd 70 8f 6f a1 ed 65 11 4d 68 d2 34 3e 7c 2f 1d
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="sample-v2-seipd-packet">
<section anchor="sample-v2-seipd-packet"><name>Sample v2 SEIPD packet</name> <name>Sample v2 SEIPD Packet</name>
<t>This packet contains the following series of octets:</t>
<t>This packet contains the following series of octets:</t> <artwork name="x25519-v2seipd-aes128-ocb.hexdump"><![CDATA[
<figure><artwork name="x25519-v2seipd-aes128-ocb.hexdump"><![CDATA[
0x0000 d2 69 02 07 02 06 61 64 0x0000 d2 69 02 07 02 06 61 64
0x0008 16 53 5b e0 b0 71 6d 60 0x0008 16 53 5b e0 b0 71 6d 60
0x0010 e0 52 a5 6c 4c 40 7f 9e 0x0010 e0 52 a5 6c 4c 40 7f 9e
0x0018 b3 6b 0e fa fe 9a d0 a0 0x0018 b3 6b 0e fa fe 9a d0 a0
0x0020 df 9b 03 3c 69 a2 1b a9 0x0020 df 9b 03 3c 69 a2 1b a9
0x0028 eb d2 c0 ec 95 bf 56 9d 0x0028 eb d2 c0 ec 95 bf 56 9d
0x0030 25 c9 99 ee 4a 3d e1 70 0x0030 25 c9 99 ee 4a 3d e1 70
0x0038 58 f4 0d fa 8b 4c 68 2b 0x0038 58 f4 0d fa 8b 4c 68 2b
0x0040 e3 fb bb d7 b2 7e b0 f5 0x0040 e3 fb bb d7 b2 7e b0 f5
0x0048 9b b5 00 5f 80 c7 c6 f4 0x0048 9b b5 00 5f 80 c7 c6 f4
0x0050 03 88 c3 0a d4 06 ab 05 0x0050 03 88 c3 0a d4 06 ab 05
0x0058 13 dc d6 f9 fd 73 76 56 0x0058 13 dc d6 f9 fd 73 76 56
0x0060 28 6e 11 77 d0 0f 88 8a 0x0060 28 6e 11 77 d0 0f 88 8a
0x0068 db 31 c4 0x0068 db 31 c4
]]></artwork></figure> ]]></artwork>
<t>The same data, broken out by octet and semantics, is:</t>
<t>The same data, broken out by octet and semantics:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 d2 packet type: SEIPD 0x0000 d2 packet type: SEIPD
0x0001 69 packet length 0x0001 69 packet length
0x0002 02 SEIPD version 2 0x0002 02 v2 SEIPD
0x0003 07 cipher: AES128 0x0003 07 cipher: AES128
0x0004 02 AEAD mode: OCB 0x0004 02 AEAD mode: OCB
0x0005 06 chunk size (2**12 octets) 0x0005 06 chunk size (2^12 octets)
0x0006 61 64 salt 0x0006 61 64 salt
0x0008 16 53 5b e0 b0 71 6d 60 0x0008 16 53 5b e0 b0 71 6d 60
0x0010 e0 52 a5 6c 4c 40 7f 9e 0x0010 e0 52 a5 6c 4c 40 7f 9e
0x0018 b3 6b 0e fa fe 9a d0 a0 0x0018 b3 6b 0e fa fe 9a d0 a0
0x0020 df 9b 03 3c 69 a2 0x0020 df 9b 03 3c 69 a2
0x0026 1b a9 chunk #0 encrypted data 0x0026 1b a9 chunk #0 encrypted data
0x0028 eb d2 c0 ec 95 bf 56 9d 0x0028 eb d2 c0 ec 95 bf 56 9d
0x0030 25 c9 99 ee 4a 3d e1 70 0x0030 25 c9 99 ee 4a 3d e1 70
0x0038 58 f4 0d fa 8b 4c 68 2b 0x0038 58 f4 0d fa 8b 4c 68 2b
0x0040 e3 fb bb d7 b2 7e b0 f5 0x0040 e3 fb bb d7 b2 7e b0 f5
0x0048 9b b5 00 0x0048 9b b5 00
0x004b 5f 80 c7 c6 f4 chunk #0 AEAD tag 0x004b 5f 80 c7 c6 f4 chunk #0 AEAD tag
0x0050 03 88 c3 0a d4 06 ab 05 0x0050 03 88 c3 0a d4 06 ab 05
0x0058 13 dc d6 0x0058 13 dc d6
0x005b f9 fd 73 76 56 final AEAD tag (#1) 0x005b f9 fd 73 76 56 final AEAD tag (#1)
0x0060 28 6e 11 77 d0 0f 88 8a S0x0060 28 6e 11 77 d0 0f 88 8a
0x0068 db 31 c4 0x0068 db 31 c4
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="decryption-of-data">
<section anchor="decryption-of-data"><name>Decryption of data</name> <name>Decryption of Data</name>
<t>Starting AEAD-OCB decryption of data, using the session key.</t>
<t>Starting AEAD-OCB decryption of data, using the session key.</t> <t>HKDF info:</t>
<artwork><![CDATA[
<t>HKDF info:</t>
<figure><artwork><![CDATA[
d2 02 07 02 06 d2 02 07 02 06
]]></artwork></figure> ]]></artwork>
<t>HKDF output:</t>
<t>HKDF output:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
45 12 f7 14 9d 86 33 41 52 7c 65 67 d5 bf fc 42 45 12 f7 14 9d 86 33 41 52 7c 65 67 d5 bf fc 42
5f af 32 50 21 2f f9 5f af 32 50 21 2f f9
]]></artwork></figure> ]]></artwork>
<t>Message key:</t>
<t>Message key:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
45 12 f7 14 9d 86 33 41 52 7c 65 67 d5 bf fc 42 45 12 f7 14 9d 86 33 41 52 7c 65 67 d5 bf fc 42
]]></artwork></figure> ]]></artwork>
<t>Initialization vector:</t>
<t>Initialization vector:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
5f af 32 50 21 2f f9 5f af 32 50 21 2f f9
]]></artwork></figure> ]]></artwork>
<t>Chunk #0:</t>
<t>Chunk #0:</t> <t>Nonce:</t>
<artwork><![CDATA[
<t>Nonce:</t>
<figure><artwork><![CDATA[
5f af 32 50 21 2f f9 00 00 00 00 00 00 00 00 5f af 32 50 21 2f f9 00 00 00 00 00 00 00 00
]]></artwork></figure> ]]></artwork>
<t>Additional authenticated data:</t>
<t>Additional authenticated data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d2 02 07 02 06 d2 02 07 02 06
]]></artwork></figure> ]]></artwork>
<t>Encrypted data chunk:</t>
<t>Encrypted data chunk:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
1b a9 eb d2 c0 ec 95 bf 56 9d 25 c9 99 ee 4a 3d 1b a9 eb d2 c0 ec 95 bf 56 9d 25 c9 99 ee 4a 3d
e1 70 58 f4 0d fa 8b 4c 68 2b e3 fb bb d7 b2 7e e1 70 58 f4 0d fa 8b 4c 68 2b e3 fb bb d7 b2 7e
b0 f5 9b b5 00 5f 80 c7 c6 f4 03 88 c3 0a d4 06 b0 f5 9b b5 00 5f 80 c7 c6 f4 03 88 c3 0a d4 06
ab 05 13 dc d6 ab 05 13 dc d6
]]></artwork></figure> ]]></artwork>
<t>Decrypted chunk #0.</t>
<t>Decrypted chunk #0.</t> <t>Literal Data packet with the string contents <tt>Hello, world!</tt>
:</t>
<t>Literal data packet with the string contents <spanx style="verb">Hello, world <artwork><![CDATA[
!</spanx>:</t>
<figure><artwork><![CDATA[
cb 13 62 00 00 00 00 00 48 65 6c 6c 6f 2c 20 77 cb 13 62 00 00 00 00 00 48 65 6c 6c 6f 2c 20 77
6f 72 6c 64 21 6f 72 6c 64 21
]]></artwork></figure> ]]></artwork>
<t>Padding packet:</t>
<t>Padding packet:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d5 0e c5 a2 93 07 29 91 62 81 47 d7 2c 8f 86 b7 d5 0e c5 a2 93 07 29 91 62 81 47 d7 2c 8f 86 b7
]]></artwork></figure> ]]></artwork>
<t>Authenticating final tag:</t>
<t>Authenticating final tag:</t> <t>Final nonce:</t>
<artwork><![CDATA[
<t>Final nonce:</t>
<figure><artwork><![CDATA[
5f af 32 50 21 2f f9 00 00 00 00 00 00 00 01 5f af 32 50 21 2f f9 00 00 00 00 00 00 00 01
]]></artwork></figure> ]]></artwork>
<t>Final additional authenticated data:</t>
<t>Final additional authenticated data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d2 02 07 02 06 00 00 00 00 00 00 00 25 d2 02 07 02 06 00 00 00 00 00 00 00 25
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="complete-x25519-aead-ocb-encrypted-packet-sequence">
<section anchor="complete-x25519-aead-ocb-encrypted-packet-sequence"><name>Compl <name>Complete X25519-AEAD-OCB Encrypted Packet Sequence</name>
ete X25519-AEAD-OCB encrypted packet sequence</name> <sourcecode type="application/pgp-encrypted" name="v6pkesk-aes128-ocb.
pgp"><![CDATA[
<figure><sourcecode type="application/pgp-encrypted" name="v6pkesk-aes128-ocb.pg
p"><![CDATA[
-----BEGIN PGP MESSAGE----- -----BEGIN PGP MESSAGE-----
wV0GIQYSyD8ecG9jCP4VGkF3Q6HwM3kOk+mXhIjR2zeNqZMIhRmHzxjV8bU/gXzO wV0GIQYSyD8ecG9jCP4VGkF3Q6HwM3kOk+mXhIjR2zeNqZMIhRmHzxjV8bU/gXzO
WgBM85PMiVi93AZfJfhK9QmxfdNnZBjeo1VDeVZheQHgaVf7yopqR6W1FT6NOrfS WgBM85PMiVi93AZfJfhK9QmxfdNnZBjeo1VDeVZheQHgaVf7yopqR6W1FT6NOrfS
aQIHAgZhZBZTW+CwcW1g4FKlbExAf56zaw76/prQoN+bAzxpohup69LA7JW/Vp0l aQIHAgZhZBZTW+CwcW1g4FKlbExAf56zaw76/prQoN+bAzxpohup69LA7JW/Vp0l
yZnuSj3hcFj0DfqLTGgr4/u717J+sPWbtQBfgMfG9AOIwwrUBqsFE9zW+f1zdlYo yZnuSj3hcFj0DfqLTGgr4/u717J+sPWbtQBfgMfG9AOIwwrUBqsFE9zW+f1zdlYo
bhF30A+IitsxxA== bhF30A+IitsxxA==
-----END PGP MESSAGE----- -----END PGP MESSAGE-----
]]></sourcecode></figure> ]]></sourcecode>
</section>
</section> </section>
</section> <section anchor="sample-aead-eax-encryption-and-decryption">
<section anchor="sample-aead-eax-encryption-and-decryption"><name>Sample AEAD-EA <name>Sample AEAD-EAX Encryption and Decryption</name>
X encryption and decryption</name> <t>This example encrypts the cleartext string <tt>Hello, world!</tt> wit
h the passphrase <tt>password</tt>, using AES-128 with AEAD-EAX encryption.</t>
<t>This example encrypts the cleartext string <spanx style="verb">Hello, world!< <section anchor="sample-symmetric-key-encrypted-session-key-packet-v6">
/spanx> with the passphrase <spanx style="verb">password</spanx>, using AES-128 <name>Sample Version 6 Symmetric Key Encrypted Session Key Packet</nam
with AEAD-EAX encryption.</t> e>
<t>This packet contains the following series of octets:</t>
<section anchor="sample-symmetric-key-encrypted-session-key-packet-v6"><name>Sam <artwork name="v6skesk-aes128-eax.hexdump"><![CDATA[
ple symmetric-key encrypted session key packet (v6)</name>
<t>This packet contains the following series of octets:</t>
<figure><artwork name="v6skesk-aes128-eax.hexdump"><![CDATA[
0x0000 c3 40 06 1e 07 01 0b 03 0x0000 c3 40 06 1e 07 01 0b 03
0x0008 08 a5 ae 57 9d 1f c5 d8 0x0008 08 a5 ae 57 9d 1f c5 d8
0x0010 2b ff 69 22 4f 91 99 93 0x0010 2b ff 69 22 4f 91 99 93
0x0018 b3 50 6f a3 b5 9a 6a 73 0x0018 b3 50 6f a3 b5 9a 6a 73
0x0020 cf f8 c5 ef c5 f4 1c 57 0x0020 cf f8 c5 ef c5 f4 1c 57
0x0028 fb 54 e1 c2 26 81 5d 78 0x0028 fb 54 e1 c2 26 81 5d 78
0x0030 28 f5 f9 2c 45 4e b6 5e 0x0030 28 f5 f9 2c 45 4e b6 5e
0x0038 be 00 ab 59 86 c6 8e 6e 0x0038 be 00 ab 59 86 c6 8e 6e
0x0040 7c 55 0x0040 7c 55
]]></artwork></figure> ]]></artwork>
<t>The same data, broken out by octet and semantics, is:</t>
<t>The same data, broken out by octet and semantics:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 c3 packet type: SKESK 0x0000 c3 packet type: SKESK
0x0001 40 packet length 0x0001 40 packet length
0x0002 06 SKESK version 6 0x0002 06 v6 SKESK
0x0003 1e length through end of AEAD nonce 0x0003 1e length through end of AEAD nonce
0x0004 07 cipher: AES128 0x0004 07 cipher: AES128
0x0005 01 AEAD mode: EAX 0x0005 01 AEAD mode: EAX
0x0006 0b length of S2K 0x0006 0b length of S2K
0x0007 03 S2K type: iterated+salted 0x0007 03 S2K type: iterated+salted
0x0008 08 S2K hash: SHA2-256 0x0008 08 S2K hash: SHA2-256
0x0009 a5 ae 57 9d 1f c5 d8 S2K salt 0x0009 a5 ae 57 9d 1f c5 d8 S2K salt
0x0010 2b 0x0010 2b
0x0011 ff S2K iterations (65011712 octets) 0x0011 ff S2K iterations (65011712 octets)
0x0012 69 22 4f 91 99 93 AEAD nonce 0x0012 69 22 4f 91 99 93 AEAD nonce
0x0018 b3 50 6f a3 b5 9a 6a 73 0x0018 b3 50 6f a3 b5 9a 6a 73
0x0020 cf f8 0x0020 cf f8
0x0022 c5 ef c5 f4 1c 57 encrypted session key 0x0022 c5 ef c5 f4 1c 57 encrypted session key
0x0028 fb 54 e1 c2 26 81 5d 78 0x0028 fb 54 e1 c2 26 81 5d 78
0x0030 28 f5 0x0030 28 f5
0x0032 f9 2c 45 4e b6 5e AEAD tag 0x0032 f9 2c 45 4e b6 5e AEAD tag
0x0038 be 00 ab 59 86 c6 8e 6e 0x0038 be 00 ab 59 86 c6 8e 6e
0x0040 7c 55 0x0040 7c 55
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="starting-aead-eax-decryption-of-the-session-key">
<section anchor="starting-aead-eax-decryption-of-the-session-key"><name>Starting <name>Starting AEAD-EAX Decryption of the Session Key</name>
AEAD-EAX decryption of the session key</name> <t>The derived key is:</t>
<artwork><![CDATA[
<t>The derived key is:</t>
<figure><artwork><![CDATA[
15 49 67 e5 90 aa 1f 92 3e 1c 0a c6 4c 88 f2 3d 15 49 67 e5 90 aa 1f 92 3e 1c 0a c6 4c 88 f2 3d
]]></artwork></figure> ]]></artwork>
<t>HKDF info:</t>
<t>HKDF info:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
c3 06 07 01 c3 06 07 01
]]></artwork></figure> ]]></artwork>
<t>HKDF output:</t>
<t>HKDF output:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
2f ce 33 1f 39 dd 95 5c c4 1e 95 d8 70 c7 21 39 2f ce 33 1f 39 dd 95 5c c4 1e 95 d8 70 c7 21 39
]]></artwork></figure> ]]></artwork>
<t>Authenticated Data:</t>
<t>Authenticated Data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
c3 06 07 01 c3 06 07 01
]]></artwork></figure> ]]></artwork>
<t>Nonce:</t>
<t>Nonce:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
69 22 4f 91 99 93 b3 50 6f a3 b5 9a 6a 73 cf f8 69 22 4f 91 99 93 b3 50 6f a3 b5 9a 6a 73 cf f8
]]></artwork></figure> ]]></artwork>
<t>Decrypted session key:</t>
<t>Decrypted session key:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
38 81 ba fe 98 54 12 45 9b 86 c3 6f 98 cb 9a 5e 38 81 ba fe 98 54 12 45 9b 86 c3 6f 98 cb 9a 5e
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="sample-v2-seipd-packet-1">
<section anchor="sample-v2-seipd-packet-1"><name>Sample v2 SEIPD packet</name> <name>Sample v2 SEIPD Packet</name>
<t>This packet contains the following series of octets:</t>
<t>This packet contains the following series of octets:</t> <artwork name="v2seipd-aes128-eax.hexdump"><![CDATA[
<figure><artwork name="v2seipd-aes128-eax.hexdump"><![CDATA[
0x0000 d2 69 02 07 01 06 9f f9 0x0000 d2 69 02 07 01 06 9f f9
0x0008 0e 3b 32 19 64 f3 a4 29 0x0008 0e 3b 32 19 64 f3 a4 29
0x0010 13 c8 dc c6 61 93 25 01 0x0010 13 c8 dc c6 61 93 25 01
0x0018 52 27 ef b7 ea ea a4 9f 0x0018 52 27 ef b7 ea ea a4 9f
0x0020 04 c2 e6 74 17 5d 4a 3d 0x0020 04 c2 e6 74 17 5d 4a 3d
0x0028 22 6e d6 af cb 9c a9 ac 0x0028 22 6e d6 af cb 9c a9 ac
0x0030 12 2c 14 70 e1 1c 63 d4 0x0030 12 2c 14 70 e1 1c 63 d4
0x0038 c0 ab 24 1c 6a 93 8a d4 0x0038 c0 ab 24 1c 6a 93 8a d4
0x0040 8b f9 9a 5a 99 b9 0b ba 0x0040 8b f9 9a 5a 99 b9 0b ba
0x0048 83 25 de 61 04 75 40 25 0x0048 83 25 de 61 04 75 40 25
0x0050 8a b7 95 9a 95 ad 05 1d 0x0050 8a b7 95 9a 95 ad 05 1d
0x0058 da 96 eb 15 43 1d fe f5 0x0058 da 96 eb 15 43 1d fe f5
0x0060 f5 e2 25 5c a7 82 61 54 0x0060 f5 e2 25 5c a7 82 61 54
0x0068 6e 33 9a 0x0068 6e 33 9a
]]></artwork></figure> ]]></artwork>
<t>The same data, broken out by octet and semantics, is:</t>
<t>The same data, broken out by octet and semantics:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 d2 packet type: SEIPD 0x0000 d2 packet type: SEIPD
0x0001 69 packet length 0x0001 69 packet length
0x0002 02 SEIPD version 2 0x0002 02 v2 SEIPD
0x0003 07 cipher: AES128 0x0003 07 cipher: AES128
0x0004 01 AEAD mode: EAX 0x0004 01 AEAD mode: EAX
0x0005 06 chunk size (2**12 octets) 0x0005 06 chunk size (2^12 octets)
0x0005 9f f9 salt 0x0005 9f f9 salt
0x0008 0e 3b 32 19 64 f3 a4 29 0x0008 0e 3b 32 19 64 f3 a4 29
0x0010 13 c8 dc c6 61 93 25 01 0x0010 13 c8 dc c6 61 93 25 01
0x0018 52 27 ef b7 ea ea a4 9f 0x0018 52 27 ef b7 ea ea a4 9f
0x0020 04 c2 e6 74 17 5d 0x0020 04 c2 e6 74 17 5d
0x0026 4a 3d chunk #0 encrypted data 0x0026 4a 3d chunk #0 encrypted data
0x0028 22 6e d6 af cb 9c a9 ac 0x0028 22 6e d6 af cb 9c a9 ac
0x0030 12 2c 14 70 e1 1c 63 d4 0x0030 12 2c 14 70 e1 1c 63 d4
0x0038 c0 ab 24 1c 6a 93 8a d4 0x0038 c0 ab 24 1c 6a 93 8a d4
0x0040 8b f9 9a 5a 99 b9 0b ba 0x0040 8b f9 9a 5a 99 b9 0b ba
0x0048 83 25 de 0x0048 83 25 de
0x004b 61 04 75 40 25 chunk #0 AEAD tag 0x004b 61 04 75 40 25 chunk #0 AEAD tag
0x0050 8a b7 95 9a 95 ad 05 1d 0x0050 8a b7 95 9a 95 ad 05 1d
0x0058 da 96 eb 0x0058 da 96 eb
0x005b 15 43 1d fe f5 final AEAD tag (#1) 0x005b 15 43 1d fe f5 final AEAD tag (#1)
0x0060 f5 e2 25 5c a7 82 61 54 0x0060 f5 e2 25 5c a7 82 61 54
0x0068 6e 33 9a 0x0068 6e 33 9a
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="decryption-of-data-1">
<section anchor="decryption-of-data-1"><name>Decryption of data</name> <name>Decryption of Data</name>
<t>Starting AEAD-EAX decryption of data, using the session key.</t>
<t>Starting AEAD-EAX decryption of data, using the session key.</t> <t>HKDF info:</t>
<artwork><![CDATA[
<t>HKDF info:</t>
<figure><artwork><![CDATA[
d2 02 07 01 06 d2 02 07 01 06
]]></artwork></figure> ]]></artwork>
<t>HKDF output:</t>
<t>HKDF output:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
b5 04 22 ac 1c 26 be 9d dd 83 1d 5b bb 36 b6 4f b5 04 22 ac 1c 26 be 9d dd 83 1d 5b bb 36 b6 4f
78 b8 33 f2 e9 4a 60 c0 78 b8 33 f2 e9 4a 60 c0
]]></artwork></figure> ]]></artwork>
<t>Message key:</t>
<t>Message key:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
b5 04 22 ac 1c 26 be 9d dd 83 1d 5b bb 36 b6 4f b5 04 22 ac 1c 26 be 9d dd 83 1d 5b bb 36 b6 4f
]]></artwork></figure> ]]></artwork>
<t>Initialization vector:</t>
<t>Initialization vector:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
78 b8 33 f2 e9 4a 60 c0 78 b8 33 f2 e9 4a 60 c0
]]></artwork></figure> ]]></artwork>
<t>Chunk #0:</t>
<t>Chunk #0:</t> <t>Nonce:</t>
<artwork><![CDATA[
<t>Nonce:</t>
<figure><artwork><![CDATA[
78 b8 33 f2 e9 4a 60 c0 00 00 00 00 00 00 00 00 78 b8 33 f2 e9 4a 60 c0 00 00 00 00 00 00 00 00
]]></artwork></figure> ]]></artwork>
<t>Additional authenticated data:</t>
<t>Additional authenticated data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d2 02 07 01 06 d2 02 07 01 06
]]></artwork></figure> ]]></artwork>
<t>Decrypted chunk #0.</t>
<t>Decrypted chunk #0.</t> <t>Literal Data packet with the string contents <tt>Hello, world!</tt>
:</t>
<t>Literal data packet with the string contents <spanx style="verb">Hello, world <artwork><![CDATA[
!</spanx>:</t>
<figure><artwork><![CDATA[
cb 13 62 00 00 00 00 00 48 65 6c 6c 6f 2c 20 77 cb 13 62 00 00 00 00 00 48 65 6c 6c 6f 2c 20 77
6f 72 6c 64 21 6f 72 6c 64 21
]]></artwork></figure> ]]></artwork>
<t>Padding packet:</t>
<t>Padding packet:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d5 0e ae 5b f0 cd 67 05 50 03 55 81 6c b0 c8 ff d5 0e ae 5b f0 cd 67 05 50 03 55 81 6c b0 c8 ff
]]></artwork></figure> ]]></artwork>
<t>Authenticating final tag:</t>
<t>Authenticating final tag:</t> <t>Final nonce:</t>
<artwork><![CDATA[
<t>Final nonce:</t>
<figure><artwork><![CDATA[
78 b8 33 f2 e9 4a 60 c0 00 00 00 00 00 00 00 01 78 b8 33 f2 e9 4a 60 c0 00 00 00 00 00 00 00 01
]]></artwork></figure> ]]></artwork>
<t>Final additional authenticated data:</t>
<t>Final additional authenticated data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d2 02 07 01 06 00 00 00 00 00 00 00 25 d2 02 07 01 06 00 00 00 00 00 00 00 25
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="complete-aead-eax-encrypted-packet-sequence">
<section anchor="complete-aead-eax-encrypted-packet-sequence"><name>Complete AEA <name>Complete AEAD-EAX Encrypted Packet Sequence</name>
D-EAX encrypted packet sequence</name> <sourcecode type="application/pgp-encrypted" name="v6skesk-aes128-eax.
pgp"><![CDATA[
<figure><sourcecode type="application/pgp-encrypted" name="v6skesk-aes128-eax.pg
p"><![CDATA[
-----BEGIN PGP MESSAGE----- -----BEGIN PGP MESSAGE-----
w0AGHgcBCwMIpa5XnR/F2Cv/aSJPkZmTs1Bvo7WaanPP+MXvxfQcV/tU4cImgV14 w0AGHgcBCwMIpa5XnR/F2Cv/aSJPkZmTs1Bvo7WaanPP+MXvxfQcV/tU4cImgV14
KPX5LEVOtl6+AKtZhsaObnxV0mkCBwEGn/kOOzIZZPOkKRPI3MZhkyUBUifvt+rq KPX5LEVOtl6+AKtZhsaObnxV0mkCBwEGn/kOOzIZZPOkKRPI3MZhkyUBUifvt+rq
pJ8EwuZ0F11KPSJu1q/LnKmsEiwUcOEcY9TAqyQcapOK1Iv5mlqZuQu6gyXeYQR1 pJ8EwuZ0F11KPSJu1q/LnKmsEiwUcOEcY9TAqyQcapOK1Iv5mlqZuQu6gyXeYQR1
QCWKt5Wala0FHdqW6xVDHf719eIlXKeCYVRuM5o= QCWKt5Wala0FHdqW6xVDHf719eIlXKeCYVRuM5o=
-----END PGP MESSAGE----- -----END PGP MESSAGE-----
]]></sourcecode></figure> ]]></sourcecode>
</section>
</section> </section>
</section> <section anchor="sample-aead-ocb-encryption-and-decryption">
<section anchor="sample-aead-ocb-encryption-and-decryption"><name>Sample AEAD-OC <name>Sample AEAD-OCB Encryption and Decryption</name>
B encryption and decryption</name> <t>This example encrypts the cleartext string <tt>Hello, world!</tt> wit
h the passphrase <tt>password</tt>, using AES-128 with AEAD-OCB encryption.</t>
<t>This example encrypts the cleartext string <spanx style="verb">Hello, world!< <section anchor="sample-symmetric-key-encrypted-session-key-packet-v6-1"
/spanx> with the passphrase <spanx style="verb">password</spanx>, using AES-128 >
with AEAD-OCB encryption.</t> <name>Sample Version 6 Symmetric Key Encrypted Session Key Packet</nam
e>
<section anchor="sample-symmetric-key-encrypted-session-key-packet-v6-1"><name>S <t>This packet contains the following series of octets:</t>
ample symmetric-key encrypted session key packet (v6)</name> <artwork name="v6skesk-aes128-ocb.hexdump"><![CDATA[
<t>This packet contains the following series of octets:</t>
<figure><artwork name="v6skesk-aes128-ocb.hexdump"><![CDATA[
0x0000 c3 3f 06 1d 07 02 0b 03 0x0000 c3 3f 06 1d 07 02 0b 03
0x0008 08 56 a2 98 d2 f5 e3 64 0x0008 08 56 a2 98 d2 f5 e3 64
0x0010 53 ff cf cc 5c 11 66 4e 0x0010 53 ff cf cc 5c 11 66 4e
0x0018 db 9d b4 25 90 d7 dc 46 0x0018 db 9d b4 25 90 d7 dc 46
0x0020 b0 72 41 b6 12 c3 81 2c 0x0020 b0 72 41 b6 12 c3 81 2c
0x0028 ff fb ea 00 f2 34 7b 25 0x0028 ff fb ea 00 f2 34 7b 25
0x0030 64 11 23 f8 87 ae 60 d4 0x0030 64 11 23 f8 87 ae 60 d4
0x0038 fd 61 4e 08 37 d8 19 d3 0x0038 fd 61 4e 08 37 d8 19 d3
0x0040 6c 0x0040 6c
]]></artwork></figure> ]]></artwork>
<t>The same data, broken out by octet and semantics, is:</t>
<t>The same data, broken out by octet and semantics:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 c3 packet type: SKESK 0x0000 c3 packet type: SKESK
0x0001 3f packet length 0x0001 3f packet length
0x0002 06 SKESK version 6 0x0002 06 v6 SKESK
0x0003 1d length through end of AEAD nonce 0x0003 1d length through end of AEAD nonce
0x0004 07 cipher: AES128 0x0004 07 cipher: AES128
0x0005 02 AEAD mode: OCB 0x0005 02 AEAD mode: OCB
0x0006 0b length of S2K 0x0006 0b length of S2K
0x0007 03 S2K type: iterated+salted 0x0007 03 S2K type: iterated+salted
0x0008 08 S2K hash: SHA2-256 0x0008 08 S2K hash: SHA2-256
0x0009 56 a2 98 d2 f5 e3 64 S2K salt 0x0009 56 a2 98 d2 f5 e3 64 S2K salt
0x0010 53 0x0010 53
0x0011 ff S2K iterations (65011712 octets) 0x0011 ff S2K iterations (65011712 octets)
0x0012 cf cc 5c 11 66 4e AEAD nonce 0x0012 cf cc 5c 11 66 4e AEAD nonce
0x0018 db 9d b4 25 90 d7 dc 46 0x0018 db 9d b4 25 90 d7 dc 46
0x0020 b0 0x0020 b0
0x0021 72 41 b6 12 c3 81 2c encrypted session key 0x0021 72 41 b6 12 c3 81 2c encrypted session key
0x0028 ff fb ea 00 f2 34 7b 25 0x0028 ff fb ea 00 f2 34 7b 25
0x0030 64 0x0030 64
0x0031 11 23 f8 87 ae 60 d4 AEAD tag 0x0031 11 23 f8 87 ae 60 d4 AEAD tag
0x0038 fd 61 4e 08 37 d8 19 d3 0x0038 fd 61 4e 08 37 d8 19 d3
0x0040 6c 0x0040 6c
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="starting-aead-ocb-decryption-of-the-session-key">
<section anchor="starting-aead-ocb-decryption-of-the-session-key"><name>Starting <name>Starting AEAD-OCB Decryption of the Session Key</name>
AEAD-OCB decryption of the session key</name> <t>The derived key is:</t>
<artwork><![CDATA[
<t>The derived key is:</t>
<figure><artwork><![CDATA[
e8 0d e2 43 a3 62 d9 3b 9d c6 07 ed e9 6a 73 56 e8 0d e2 43 a3 62 d9 3b 9d c6 07 ed e9 6a 73 56
]]></artwork></figure> ]]></artwork>
<t>HKDF info:</t>
<t>HKDF info:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
c3 06 07 02 c3 06 07 02
]]></artwork></figure> ]]></artwork>
<t>HKDF output:</t>
<t>HKDF output:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
38 a9 b3 45 b5 68 0b b6 1b b6 5d 73 ee c7 ec d9 38 a9 b3 45 b5 68 0b b6 1b b6 5d 73 ee c7 ec d9
]]></artwork></figure> ]]></artwork>
<t>Authenticated Data:</t>
<t>Authenticated Data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
c3 06 07 02 c3 06 07 02
]]></artwork></figure> ]]></artwork>
<t>Nonce:</t>
<t>Nonce:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
cf cc 5c 11 66 4e db 9d b4 25 90 d7 dc 46 b0 cf cc 5c 11 66 4e db 9d b4 25 90 d7 dc 46 b0
]]></artwork></figure> ]]></artwork>
<t>Decrypted session key:</t>
<t>Decrypted session key:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
28 e7 9a b8 23 97 d3 c6 3d e2 4a c2 17 d7 b7 91 28 e7 9a b8 23 97 d3 c6 3d e2 4a c2 17 d7 b7 91
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="sample-v2-seipd-packet-2">
<section anchor="sample-v2-seipd-packet-2"><name>Sample v2 SEIPD packet</name> <name>Sample v2 SEIPD Packet</name>
<t>This packet contains the following series of octets:</t>
<t>This packet contains the following series of octets:</t> <artwork name="v2seipd-aes128-ocb.hexdump"><![CDATA[
<figure><artwork name="v2seipd-aes128-ocb.hexdump"><![CDATA[
0x0000 d2 69 02 07 02 06 20 a6 0x0000 d2 69 02 07 02 06 20 a6
0x0008 61 f7 31 fc 9a 30 32 b5 0x0008 61 f7 31 fc 9a 30 32 b5
0x0010 62 33 26 02 7e 3a 5d 8d 0x0010 62 33 26 02 7e 3a 5d 8d
0x0018 b5 74 8e be ff 0b 0c 59 0x0018 b5 74 8e be ff 0b 0c 59
0x0020 10 d0 9e cd d6 41 ff 9f 0x0020 10 d0 9e cd d6 41 ff 9f
0x0028 d3 85 62 75 80 35 bc 49 0x0028 d3 85 62 75 80 35 bc 49
0x0030 75 4c e1 bf 3f ff a7 da 0x0030 75 4c e1 bf 3f ff a7 da
0x0038 d0 a3 b8 10 4f 51 33 cf 0x0038 d0 a3 b8 10 4f 51 33 cf
0x0040 42 a4 10 0a 83 ee f4 ca 0x0040 42 a4 10 0a 83 ee f4 ca
0x0048 1b 48 01 a8 84 6b f4 2b 0x0048 1b 48 01 a8 84 6b f4 2b
0x0050 cd a7 c8 ce 9d 65 e2 12 0x0050 cd a7 c8 ce 9d 65 e2 12
0x0058 f3 01 cb cd 98 fd ca de 0x0058 f3 01 cb cd 98 fd ca de
0x0060 69 4a 87 7a d4 24 73 23 0x0060 69 4a 87 7a d4 24 73 23
0x0068 f6 e8 57 0x0068 f6 e8 57
]]></artwork></figure> ]]></artwork>
<t>The same data, broken out by octet and semantics, is:</t>
<t>The same data, broken out by octet and semantics:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 d2 packet type: SEIPD 0x0000 d2 packet type: SEIPD
0x0001 69 packet length 0x0001 69 packet length
0x0002 02 SEIPD version 2 0x0002 02 v2 SEIPD
0x0003 07 cipher: AES128 0x0003 07 cipher: AES128
0x0004 02 AEAD mode: OCB 0x0004 02 AEAD mode: OCB
0x0005 06 chunk size (2**21 octets) 0x0005 06 chunk size (2^12 octets)
0x0006 20 a6 salt 0x0006 20 a6 salt
0x0008 61 f7 31 fc 9a 30 32 b5 0x0008 61 f7 31 fc 9a 30 32 b5
0x0010 62 33 26 02 7e 3a 5d 8d 0x0010 62 33 26 02 7e 3a 5d 8d
0x0018 b5 74 8e be ff 0b 0c 59 0x0018 b5 74 8e be ff 0b 0c 59
0x0020 10 d0 9e cd d6 41 0x0020 10 d0 9e cd d6 41
0x0026 ff 9f chunk #0 encrypted data 0x0026 ff 9f chunk #0 encrypted data
0x0028 d3 85 62 75 80 35 bc 49 0x0028 d3 85 62 75 80 35 bc 49
0x0030 75 4c e1 bf 3f ff a7 da 0x0030 75 4c e1 bf 3f ff a7 da
0x0038 d0 a3 b8 10 4f 51 33 cf 0x0038 d0 a3 b8 10 4f 51 33 cf
0x0040 42 a4 10 0a 83 ee f4 ca 0x0040 42 a4 10 0a 83 ee f4 ca
0x0048 1b 48 01 0x0048 1b 48 01
0x004b a8 84 6b f4 2b chunk #0 authentication tag 0x004b a8 84 6b f4 2b chunk #0 authentication tag
0x0050 cd a7 c8 ce 9d 65 e2 12 0x0050 cd a7 c8 ce 9d 65 e2 12
0x0058 f3 01 cb 0x0058 f3 01 cb
0x005b cd 98 fd ca de final AEAD tag (#1) 0x005b cd 98 fd ca de final AEAD tag (#1)
0x0060 69 4a 87 7a d4 24 73 23 0x0060 69 4a 87 7a d4 24 73 23
0x0068 f6 e8 57 0x0068 f6 e8 57
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="decryption-of-data-2">
<section anchor="decryption-of-data-2"><name>Decryption of data</name> <name>Decryption of Data</name>
<t>Starting AEAD-OCB decryption of data, using the session key.</t>
<t>Starting AEAD-OCB decryption of data, using the session key.</t> <t>HKDF info:</t>
<artwork><![CDATA[
<t>HKDF info:</t>
<figure><artwork><![CDATA[
d2 02 07 02 06 d2 02 07 02 06
]]></artwork></figure> ]]></artwork>
<t>HKDF output:</t>
<t>HKDF output:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
71 66 2a 11 ee 5b 4e 08 14 4e 6d e8 83 a0 09 99 71 66 2a 11 ee 5b 4e 08 14 4e 6d e8 83 a0 09 99
eb de 12 bb 57 0d cf eb de 12 bb 57 0d cf
]]></artwork></figure> ]]></artwork>
<t>Message key:</t>
<t>Message key:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
71 66 2a 11 ee 5b 4e 08 14 4e 6d e8 83 a0 09 99 71 66 2a 11 ee 5b 4e 08 14 4e 6d e8 83 a0 09 99
]]></artwork></figure> ]]></artwork>
<t>Initialization vector:</t>
<t>Initialization vector:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
eb de 12 bb 57 0d cf eb de 12 bb 57 0d cf
]]></artwork></figure> ]]></artwork>
<t>Chunk #0:</t>
<t>Chunk #0:</t> <t>Nonce:</t>
<artwork><![CDATA[
<t>Nonce:</t>
<figure><artwork><![CDATA[
eb de 12 bb 57 0d cf 00 00 00 00 00 00 00 00 eb de 12 bb 57 0d cf 00 00 00 00 00 00 00 00
]]></artwork></figure> ]]></artwork>
<t>Additional authenticated data:</t>
<t>Additional authenticated data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d2 02 07 02 06 d2 02 07 02 06
]]></artwork></figure> ]]></artwork>
<t>Decrypted chunk #0.</t>
<t>Decrypted chunk #0.</t> <t>Literal Data packet with the string contents <tt>Hello, world!</tt>
:</t>
<t>Literal data packet with the string contents <spanx style="verb">Hello, world <artwork><![CDATA[
!</spanx>:</t>
<figure><artwork><![CDATA[
cb 13 62 00 00 00 00 00 48 65 6c 6c 6f 2c 20 77 cb 13 62 00 00 00 00 00 48 65 6c 6c 6f 2c 20 77
6f 72 6c 64 21 6f 72 6c 64 21
]]></artwork></figure> ]]></artwork>
<t>Padding packet:</t>
<t>Padding packet:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d5 0e ae 6a a1 64 9b 56 aa 83 5b 26 13 90 2b d2 d5 0e ae 6a a1 64 9b 56 aa 83 5b 26 13 90 2b d2
]]></artwork></figure> ]]></artwork>
<t>Authenticating final tag:</t>
<t>Authenticating final tag:</t> <t>Final nonce:</t>
<artwork><![CDATA[
<t>Final nonce:</t>
<figure><artwork><![CDATA[
eb de 12 bb 57 0d cf 00 00 00 00 00 00 00 01 eb de 12 bb 57 0d cf 00 00 00 00 00 00 00 01
]]></artwork></figure> ]]></artwork>
<t>Final additional authenticated data:</t>
<t>Final additional authenticated data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d2 02 07 02 06 00 00 00 00 00 00 00 25 d2 02 07 02 06 00 00 00 00 00 00 00 25
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="complete-aead-ocb-encrypted-packet-sequence">
<section anchor="complete-aead-ocb-encrypted-packet-sequence"><name>Complete AEA <name>Complete AEAD-OCB Encrypted Packet Sequence</name>
D-OCB encrypted packet sequence</name> <sourcecode type="application/pgp-encrypted" name="v6skesk-aes128-ocb.
pgp"><![CDATA[
<figure><sourcecode type="application/pgp-encrypted" name="v6skesk-aes128-ocb.pg
p"><![CDATA[
-----BEGIN PGP MESSAGE----- -----BEGIN PGP MESSAGE-----
wz8GHQcCCwMIVqKY0vXjZFP/z8xcEWZO2520JZDX3EawckG2EsOBLP/76gDyNHsl wz8GHQcCCwMIVqKY0vXjZFP/z8xcEWZO2520JZDX3EawckG2EsOBLP/76gDyNHsl
ZBEj+IeuYNT9YU4IN9gZ02zSaQIHAgYgpmH3MfyaMDK1YjMmAn46XY21dI6+/wsM ZBEj+IeuYNT9YU4IN9gZ02zSaQIHAgYgpmH3MfyaMDK1YjMmAn46XY21dI6+/wsM
WRDQns3WQf+f04VidYA1vEl1TOG/P/+n2tCjuBBPUTPPQqQQCoPu9MobSAGohGv0 WRDQns3WQf+f04VidYA1vEl1TOG/P/+n2tCjuBBPUTPPQqQQCoPu9MobSAGohGv0
K82nyM6dZeIS8wHLzZj9yt5pSod61CRzI/boVw== K82nyM6dZeIS8wHLzZj9yt5pSod61CRzI/boVw==
-----END PGP MESSAGE----- -----END PGP MESSAGE-----
]]></sourcecode></figure> ]]></sourcecode>
</section>
</section> </section>
</section> <section anchor="sample-aead-gcm-encryption-and-decryption">
<section anchor="sample-aead-gcm-encryption-and-decryption"><name>Sample AEAD-GC <name>Sample AEAD-GCM Encryption and Decryption</name>
M encryption and decryption</name> <t>This example encrypts the cleartext string <tt>Hello, world!</tt> wit
h the passphrase <tt>password</tt>, using AES-128 with AEAD-GCM encryption.</t>
<t>This example encrypts the cleartext string <spanx style="verb">Hello, world!< <section anchor="sample-symmetric-key-encrypted-session-key-packet-v6-2"
/spanx> with the passphrase <spanx style="verb">password</spanx>, using AES-128 >
with AEAD-GCM encryption.</t> <name>Sample Version 6 Symmetric Key Encrypted Session Key Packet</nam
e>
<section anchor="sample-symmetric-key-encrypted-session-key-packet-v6-2"><name>S <t>This packet contains the following series of octets:</t>
ample symmetric-key encrypted session key packet (v6)</name> <artwork name="v6skesk-aes128-gcm.hexdump"><![CDATA[
<t>This packet contains the following series of octets:</t>
<figure><artwork name="v6skesk-aes128-gcm.hexdump"><![CDATA[
0x0000 c3 3c 06 1a 07 03 0b 03 0x0000 c3 3c 06 1a 07 03 0b 03
0x0008 08 e9 d3 97 85 b2 07 00 0x0008 08 e9 d3 97 85 b2 07 00
0x0010 08 ff b4 2e 7c 48 3e f4 0x0010 08 ff b4 2e 7c 48 3e f4
0x0018 88 44 57 cb 37 26 b9 b3 0x0018 88 44 57 cb 37 26 b9 b3
0x0020 db 9f f7 76 e5 f4 d9 a4 0x0020 db 9f f7 76 e5 f4 d9 a4
0x0028 09 52 e2 44 72 98 85 1a 0x0028 09 52 e2 44 72 98 85 1a
0x0030 bf ff 75 26 df 2d d5 54 0x0030 bf ff 75 26 df 2d d5 54
0x0038 41 75 79 a7 79 9f 0x0038 41 75 79 a7 79 9f
]]></artwork></figure> ]]></artwork>
<t>The same data, broken out by octet and semantics, is:</t>
<t>The same data, broken out by octet and semantics:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 c3 packet type: SKESK 0x0000 c3 packet type: SKESK
0x0001 3c packet length 0x0001 3c packet length
0x0002 06 SKESK version 6 0x0002 06 v6 SKESK
0x0003 1a length through end of AEAD nonce 0x0003 1a length through end of AEAD nonce
0x0004 07 cipher: AES128 0x0004 07 cipher: AES128
0x0005 03 AEAD mode: GCM 0x0005 03 AEAD mode: GCM
0x0006 0b length of S2K 0x0006 0b length of S2K
0x0007 03 S2K type: iterated+salted 0x0007 03 S2K type: iterated+salted
0x0008 08 S2K hash: SHA2-256 0x0008 08 S2K hash: SHA2-256
0x0009 e9 d3 97 85 b2 07 00 S2K salt 0x0009 e9 d3 97 85 b2 07 00 S2K salt
0x0010 08 0x0010 08
0x0011 ff S2K iterations (65011712 octets) 0x0011 ff S2K iterations (65011712 octets)
0x0012 b4 2e 7c 48 3e f4 AEAD nonce 0x0012 b4 2e 7c 48 3e f4 AEAD nonce
0x0018 88 44 57 cb 37 26 0x0018 88 44 57 cb 37 26
0x001e b9 b3 encrypted session key 0x001e b9 b3 encrypted session key
0x0020 db 9f f7 76 e5 f4 d9 a4 0x0020 db 9f f7 76 e5 f4 d9 a4
0x0028 09 52 e2 44 72 98 0x0028 09 52 e2 44 72 98
0x002e 85 1a AEAD tag 0x002e 85 1a AEAD tag
0x0030 bf ff 75 26 df 2d d5 54 0x0030 bf ff 75 26 df 2d d5 54
0x0038 41 75 79 a7 79 9f 0x0038 41 75 79 a7 79 9f
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="starting-aead-gcm-decryption-of-the-session-key">
<section anchor="starting-aead-gcm-decryption-of-the-session-key"><name>Starting <name>Starting AEAD-GCM Decryption of the Session Key</name>
AEAD-GCM decryption of the session key</name> <t>The derived key is:</t>
<artwork><![CDATA[
<t>The derived key is:</t>
<figure><artwork><![CDATA[
25 02 81 71 5b ba 78 28 ef 71 ef 64 c4 78 47 53 25 02 81 71 5b ba 78 28 ef 71 ef 64 c4 78 47 53
]]></artwork></figure> ]]></artwork>
<t>HKDF info:</t>
<t>HKDF info:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
c3 06 07 03 c3 06 07 03
]]></artwork></figure> ]]></artwork>
<t>HKDF output:</t>
<t>HKDF output:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
7a 6f 9a b7 f9 9f 7e f8 db ef 84 1c 65 08 00 f5 7a 6f 9a b7 f9 9f 7e f8 db ef 84 1c 65 08 00 f5
]]></artwork></figure> ]]></artwork>
<t>Authenticated Data:</t>
<t>Authenticated Data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
c3 06 07 03 c3 06 07 03
]]></artwork></figure> ]]></artwork>
<t>Nonce:</t>
<t>Nonce:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
b4 2e 7c 48 3e f4 88 44 57 cb 37 26 b4 2e 7c 48 3e f4 88 44 57 cb 37 26
]]></artwork></figure> ]]></artwork>
<t>Decrypted session key:</t>
<t>Decrypted session key:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
19 36 fc 85 68 98 02 74 bb 90 0d 83 19 36 0c 77 19 36 fc 85 68 98 02 74 bb 90 0d 83 19 36 0c 77
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="sample-v2-seipd-packet-3">
<section anchor="sample-v2-seipd-packet-3"><name>Sample v2 SEIPD packet</name> <name>Sample v2 SEIPD Packet</name>
<t>This packet contains the following series of octets, is:</t>
<t>This packet contains the following series of octets:</t> <artwork name="v2seipd-aes128-ocb.hexdump"><![CDATA[
<figure><artwork name="v2seipd-aes128-ocb.hexdump"><![CDATA[
0x0000 d2 69 02 07 03 06 fc b9 0x0000 d2 69 02 07 03 06 fc b9
0x0008 44 90 bc b9 8b bd c9 d1 0x0008 44 90 bc b9 8b bd c9 d1
0x0010 06 c6 09 02 66 94 0f 72 0x0010 06 c6 09 02 66 94 0f 72
0x0018 e8 9e dc 21 b5 59 6b 15 0x0018 e8 9e dc 21 b5 59 6b 15
0x0020 76 b1 01 ed 0f 9f fc 6f 0x0020 76 b1 01 ed 0f 9f fc 6f
0x0028 c6 d6 5b bf d2 4d cd 07 0x0028 c6 d6 5b bf d2 4d cd 07
0x0030 90 96 6e 6d 1e 85 a3 00 0x0030 90 96 6e 6d 1e 85 a3 00
0x0038 53 78 4c b1 d8 b6 a0 69 0x0038 53 78 4c b1 d8 b6 a0 69
0x0040 9e f1 21 55 a7 b2 ad 62 0x0040 9e f1 21 55 a7 b2 ad 62
0x0048 58 53 1b 57 65 1f d7 77 0x0048 58 53 1b 57 65 1f d7 77
0x0050 79 12 fa 95 e3 5d 9b 40 0x0050 79 12 fa 95 e3 5d 9b 40
0x0058 21 6f 69 a4 c2 48 db 28 0x0058 21 6f 69 a4 c2 48 db 28
0x0060 ff 43 31 f1 63 29 07 39 0x0060 ff 43 31 f1 63 29 07 39
0x0068 9e 6f f9 0x0068 9e 6f f9
]]></artwork></figure> ]]></artwork>
<t>The same data, broken out by octet and semantics, is:</t>
<t>The same data, broken out by octet and semantics:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
0x0000 d2 packet type: SEIPD 0x0000 d2 packet type: SEIPD
0x0001 69 packet length 0x0001 69 packet length
0x0002 02 SEIPD version 2 0x0002 02 v2 SEIPD
0x0003 07 cipher: AES128 0x0003 07 cipher: AES128
0x0004 03 AEAD mode: GCM 0x0004 03 AEAD mode: GCM
0x0005 06 chunk size (2**21 octets) 0x0005 06 chunk size (2^12 octets)
0x0006 fc b9 salt 0x0006 fc b9 salt
0x0008 44 90 bc b9 8b bd c9 d1 0x0008 44 90 bc b9 8b bd c9 d1
0x0010 06 c6 09 02 66 94 0f 72 0x0010 06 c6 09 02 66 94 0f 72
0x0018 e8 9e dc 21 b5 59 6b 15 0x0018 e8 9e dc 21 b5 59 6b 15
0x0020 76 b1 01 ed 0f 9f 0x0020 76 b1 01 ed 0f 9f
0x0026 fc 6f chunk #0 encrypted data 0x0026 fc 6f chunk #0 encrypted data
0x0028 c6 d6 5b bf d2 4d cd 07 0x0028 c6 d6 5b bf d2 4d cd 07
0x0030 90 96 6e 6d 1e 85 a3 00 0x0030 90 96 6e 6d 1e 85 a3 00
0x0038 53 78 4c b1 d8 b6 a0 69 0x0038 53 78 4c b1 d8 b6 a0 69
0x0040 9e f1 21 55 a7 b2 ad 62 0x0040 9e f1 21 55 a7 b2 ad 62
0x0048 58 53 1b 0x0048 58 53 1b
0x004b 57 65 1f d7 77 chunk #0 authentication tag 0x004b 57 65 1f d7 77 chunk #0 authentication tag
0x0050 79 12 fa 95 e3 5d 9b 40 0x0050 79 12 fa 95 e3 5d 9b 40
0x0058 21 6f 69 0x0058 21 6f 69
0x005b a4 c2 48 db 28 final AEAD tag (#1) 0x005b a4 c2 48 db 28 final AEAD tag (#1)
0x0060 ff 43 31 f1 63 29 07 39 0x0060 ff 43 31 f1 63 29 07 39
0x0068 9e 6f f9 0x0068 9e 6f f9
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="decryption-of-data-3">
<section anchor="decryption-of-data-3"><name>Decryption of data</name> <name>Decryption of Data</name>
<t>Starting AEAD-GCM decryption of data, using the session key.</t>
<t>Starting AEAD-GCM decryption of data, using the session key.</t> <t>HKDF info:</t>
<artwork><![CDATA[
<t>HKDF info:</t>
<figure><artwork><![CDATA[
d2 02 07 03 06 d2 02 07 03 06
]]></artwork></figure> ]]></artwork>
<t>HKDF output:</t>
<t>HKDF output:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
ea 14 38 80 3c b8 a4 77 40 ce 9b 54 c3 38 77 8d ea 14 38 80 3c b8 a4 77 40 ce 9b 54 c3 38 77 8d
4d 2b dc 2b 4d 2b dc 2b
]]></artwork></figure> ]]></artwork>
<t>Message key:</t>
<t>Message key:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
ea 14 38 80 3c b8 a4 77 40 ce 9b 54 c3 38 77 8d ea 14 38 80 3c b8 a4 77 40 ce 9b 54 c3 38 77 8d
]]></artwork></figure> ]]></artwork>
<t>Initialization vector:</t>
<t>Initialization vector:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
4d 2b dc 2b 4d 2b dc 2b
]]></artwork></figure> ]]></artwork>
<t>Chunk #0:</t>
<t>Chunk #0:</t> <t>Nonce:</t>
<artwork><![CDATA[
<t>Nonce:</t>
<figure><artwork><![CDATA[
4d 2b dc 2b 00 00 00 00 00 00 00 00 4d 2b dc 2b 00 00 00 00 00 00 00 00
]]></artwork></figure> ]]></artwork>
<t>Additional authenticated data:</t>
<t>Additional authenticated data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d2 02 07 03 06 d2 02 07 03 06
]]></artwork></figure> ]]></artwork>
<t>Decrypted chunk #0.</t>
<t>Decrypted chunk #0.</t> <t>Literal Data packet with the string contents <tt>Hello, world!</tt>
:</t>
<t>Literal data packet with the string contents <spanx style="verb">Hello, world <artwork><![CDATA[
!</spanx>:</t>
<figure><artwork><![CDATA[
cb 13 62 00 00 00 00 00 48 65 6c 6c 6f 2c 20 77 cb 13 62 00 00 00 00 00 48 65 6c 6c 6f 2c 20 77
6f 72 6c 64 21 6f 72 6c 64 21
]]></artwork></figure> ]]></artwork>
<t>Padding packet:</t>
<t>Padding packet:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d5 0e 1c e2 26 9a 9e dd ef 81 03 21 72 b7 ed 7c d5 0e 1c e2 26 9a 9e dd ef 81 03 21 72 b7 ed 7c
]]></artwork></figure> ]]></artwork>
<t>Authenticating final tag:</t>
<t>Authenticating final tag:</t> <t>Final nonce:</t>
<artwork><![CDATA[
<t>Final nonce:</t>
<figure><artwork><![CDATA[
4d 2b dc 2b 00 00 00 00 00 00 00 01 4d 2b dc 2b 00 00 00 00 00 00 00 01
]]></artwork></figure> ]]></artwork>
<t>Final additional authenticated data:</t>
<t>Final additional authenticated data:</t> <artwork><![CDATA[
<figure><artwork><![CDATA[
d2 02 07 03 06 00 00 00 00 00 00 00 25 d2 02 07 03 06 00 00 00 00 00 00 00 25
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="complete-aead-gcm-encrypted-packet-sequence">
<section anchor="complete-aead-gcm-encrypted-packet-sequence"><name>Complete AEA <name>Complete AEAD-GCM Encrypted Packet Sequence</name>
D-GCM encrypted packet sequence</name> <sourcecode type="application/pgp-encrypted" name="v6skesk-aes128-gcm.
pgp"><![CDATA[
<figure><sourcecode type="application/pgp-encrypted" name="v6skesk-aes128-gcm.pg
p"><![CDATA[
-----BEGIN PGP MESSAGE----- -----BEGIN PGP MESSAGE-----
wzwGGgcDCwMI6dOXhbIHAAj/tC58SD70iERXyzcmubPbn/d25fTZpAlS4kRymIUa wzwGGgcDCwMI6dOXhbIHAAj/tC58SD70iERXyzcmubPbn/d25fTZpAlS4kRymIUa
v/91Jt8t1VRBdXmneZ/SaQIHAwb8uUSQvLmLvcnRBsYJAmaUD3LontwhtVlrFXax v/91Jt8t1VRBdXmneZ/SaQIHAwb8uUSQvLmLvcnRBsYJAmaUD3LontwhtVlrFXax
Ae0Pn/xvxtZbv9JNzQeQlm5tHoWjAFN4TLHYtqBpnvEhVaeyrWJYUxtXZR/Xd3kS Ae0Pn/xvxtZbv9JNzQeQlm5tHoWjAFN4TLHYtqBpnvEhVaeyrWJYUxtXZR/Xd3kS
+pXjXZtAIW9ppMJI2yj/QzHxYykHOZ5v+Q== +pXjXZtAIW9ppMJI2yj/QzHxYykHOZ5v+Q==
-----END PGP MESSAGE----- -----END PGP MESSAGE-----
]]></sourcecode></figure> ]]></sourcecode>
</section>
</section> </section>
</section> <section anchor="sample-messages-encrypted-using-argon2">
<section anchor="sample-messages-encrypted-using-argon2"><name>Sample messages e <name>Sample Messages Encrypted Using Argon2</name>
ncrypted using Argon2</name> <t>These messages are the literal data <tt>Hello, world!</tt> encrypted
using v1 SEIPD, with Argon2 and the passphrase "password", using different sessi
<t>These messages are the literal data "Hello, world!" encrypted using v1 SEIPD, on key sizes. In each example, the choice of symmetric cipher is the same in bot
with Argon2 and the passphrase "password", using different session key sizes. h the v4 SKESK packet and v1 SEIPD packet. In all cases, the Argon2 parameters a
In each example, the choice of symmetric cipher is the same in both the v4 SKESK re t = 1, p = 4, and m = 21.</t>
packet and v1 SEIPD packet. <section anchor="version-4-skesk-using-argon2-with-aes-128">
In all cases, the Argon2 parameters are t = 1, p = 4, and m = 21.</t> <name>V4 SKESK Using Argon2 with AES-128</name>
<sourcecode type="application/pgp-encrypted" name="v4skesk-argon2-aes1
<section anchor="version-4-skesk-using-argon2-with-aes-128"><name>Version 4 SKES 28.pgp"><![CDATA[
K using Argon2 with AES-128</name>
<figure><sourcecode type="application/pgp-encrypted" name="v4skesk-argon2-aes128
.pgp"><![CDATA[
-----BEGIN PGP MESSAGE----- -----BEGIN PGP MESSAGE-----
Comment: Encrypted using AES with 128-bit key Comment: Encrypted using AES with 128-bit key
Comment: Session key: 01FE16BBACFD1E7B78EF3B865187374F Comment: Session key: 01FE16BBACFD1E7B78EF3B865187374F
wycEBwScUvg8J/leUNU1RA7N/zE2AQQVnlL8rSLPP5VlQsunlO+ECxHSPgGYGKY+ wycEBwScUvg8J/leUNU1RA7N/zE2AQQVnlL8rSLPP5VlQsunlO+ECxHSPgGYGKY+
YJz4u6F+DDlDBOr5NRQXt/KJIf4m4mOlKyC/uqLbpnLJZMnTq3o79GxBTdIdOzhH YJz4u6F+DDlDBOr5NRQXt/KJIf4m4mOlKyC/uqLbpnLJZMnTq3o79GxBTdIdOzhH
XfA3pqV4mTzF XfA3pqV4mTzF
-----END PGP MESSAGE----- -----END PGP MESSAGE-----
]]></sourcecode></figure> ]]></sourcecode>
</section>
</section> <section anchor="version-4-skesk-using-argon2-with-aes-192">
<section anchor="version-4-skesk-using-argon2-with-aes-192"><name>Version 4 SKES <name>V4 SKESK Using Argon2 with AES-192</name>
K using Argon2 with AES-192</name> <sourcecode type="application/pgp-encrypted" name="v4skesk-argon2-aes1
92.pgp"><![CDATA[
<figure><sourcecode type="application/pgp-encrypted" name="v4skesk-argon2-aes192
.pgp"><![CDATA[
-----BEGIN PGP MESSAGE----- -----BEGIN PGP MESSAGE-----
Comment: Encrypted using AES with 192-bit key Comment: Encrypted using AES with 192-bit key
Comment: Session key: 27006DAE68E509022CE45A14E569E91001C2955... Comment: Session key: 27006DAE68E509022CE45A14E569E91001C2955...
Comment: Session key: ...AF8DFE194 Comment: Session key: ...AF8DFE194
wy8ECAThTKxHFTRZGKli3KNH4UP4AQQVhzLJ2va3FG8/pmpIPd/H/mdoVS5VBLLw wy8ECAThTKxHFTRZGKli3KNH4UP4AQQVhzLJ2va3FG8/pmpIPd/H/mdoVS5VBLLw
F9I+AdJ1Sw56PRYiKZjCvHg+2bnq02s33AJJoyBexBI4QKATFRkyez2gldJldRys F9I+AdJ1Sw56PRYiKZjCvHg+2bnq02s33AJJoyBexBI4QKATFRkyez2gldJldRys
LVg77Mwwfgl2n/d572WciAM= LVg77Mwwfgl2n/d572WciAM=
-----END PGP MESSAGE----- -----END PGP MESSAGE-----
]]></sourcecode></figure> ]]></sourcecode>
</section>
</section> <section anchor="version-4-skesk-using-argon2-with-aes-256">
<section anchor="version-4-skesk-using-argon2-with-aes-256"><name>Version 4 SKES <name>V4 SKESK Using Argon2 with AES-256</name>
K using Argon2 with AES-256</name> <sourcecode type="application/pgp-encrypted" name="v4skesk-argon2-aes2
56.pgp"><![CDATA[
<figure><sourcecode type="application/pgp-encrypted" name="v4skesk-argon2-aes256
.pgp"><![CDATA[
-----BEGIN PGP MESSAGE----- -----BEGIN PGP MESSAGE-----
Comment: Encrypted using AES with 256-bit key Comment: Encrypted using AES with 256-bit key
Comment: Session key: BBEDA55B9AAE63DAC45D4F49D89DACF4AF37FEF... Comment: Session key: BBEDA55B9AAE63DAC45D4F49D89DACF4AF37FEF...
Comment: Session key: ...C13BAB2F1F8E18FB74580D8B0 Comment: Session key: ...C13BAB2F1F8E18FB74580D8B0
wzcECQS4eJUgIG/3mcaILEJFpmJ8AQQVnZ9l7KtagdClm9UaQ/Z6M/5roklSGpGu wzcECQS4eJUgIG/3mcaILEJFpmJ8AQQVnZ9l7KtagdClm9UaQ/Z6M/5roklSGpGu
623YmaXezGj80j4B+Ku1sgTdJo87X1Wrup7l0wJypZls21Uwd67m9koF60eefH/K 623YmaXezGj80j4B+Ku1sgTdJo87X1Wrup7l0wJypZls21Uwd67m9koF60eefH/K
95D1usliXOEm8ayQJQmZrjf6K6v9PWwqMQ== 95D1usliXOEm8ayQJQmZrjf6K6v9PWwqMQ==
-----END PGP MESSAGE----- -----END PGP MESSAGE-----
]]></sourcecode></figure> ]]></sourcecode>
</section>
</section> </section>
</section> </section>
</section> <section anchor="upgrade-guidance">
<section anchor="upgrade-guidance"><name>Upgrade Guidance (Adapting Implementati <name>Upgrade Guidance (Adapting Implementations from RFCs 4880 and 6637)<
ons from RFC 4880 and RFC 6637)</name> /name>
<t>This subsection offers a concise, non-normative summary of the substant
<t>This subsection offers a concise, non-normative summary of the substantial ad ial additions to and departures from <xref target="RFC4880"/> and <xref target="
ditions to and departures from <xref target="RFC4880"/> and <xref target="RFC663 RFC6637"/>.
7"/>. It is intended to help implementers who are augmenting an existing implementatio
It is intended to help implementers who are augmenting an existing implementatio n from those specifications to comply with this specification. Cryptographic alg
n from those standards to this standard. orithms marked with "MTI" are mandatory to implement.</t>
Cryptographic algorithms marked with "MTI" are mandatory to implement.</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>Public Key Signing Algorithms:
<t>Public Key signing algorithms: </t>
<list style="symbols"> <ul spacing="normal">
<t>Ed25519 (<xref target="key-ed25519"/> and <xref target="sig-ed25519"/>) <li>
, MTI</t> <t>Ed25519 (Sections <xref target="key-ed25519" format="counter"/>
<t>Ed448 (<xref target="key-ed448"/> and <xref target="sig-ed448"/>)</t> and <xref target="sig-ed25519" format="counter"/>) -- MTI</t>
<t>EdDSALegacy with Ed25519Legacy (<xref target="key-eddsa-legacy"/> and < </li>
xref target="sig-eddsa-legacy"/>)</t> <li>
<t>ECDSA with Brainpool curves (<xref target="ec-curves"/>)</t> <t>Ed448 (Sections <xref target="key-ed448" format="counter"/> and
</list></t> <xref target="sig-ed448" format="counter"/>)</t>
<t>Public Key encryption algorithms: </li>
<list style="symbols"> <li>
<t>X25519 (<xref target="key-x25519"/> and <xref target="pkesk-x25519"/>), <t>EdDSALegacy with Ed25519Legacy (Sections <xref target="key-edds
MTI</t> a-legacy" format="counter"/> and <xref target="sig-eddsa-legacy" format="counter
<t>X448 (<xref target="key-x448"/> and <xref target="pkesk-x448"/>)</t> "/>)</t>
<t>ECDH with Curve25519Legacy (<xref target="ec-curves"/>)</t> </li>
<t>ECDH with Brainpool curves (<xref target="ec-curves"/>)</t> <li>
</list></t> <t>ECDSA with Brainpool curves (<xref target="ec-curves"/>)</t>
<t>AEAD Encryption: </li>
<list style="symbols"> </ul>
<t>Version 2 SEIPD (<xref target="version-two-seipd"/>)</t> </li>
<t>AEAD modes: <li>
<list style="symbols"> <t>Public Key Encryption Algorithms:
<t>OCB mode (<xref target="aead-mode-ocb"/>), MTI</t> </t>
<t>EAX mode (<xref target="aead-mode-eax"/>)</t> <ul spacing="normal">
<t>GCM mode (<xref target="aead-mode-gcm"/>)</t> <li>
</list></t> <t>X25519 (Sections <xref target="key-x25519" format="counter"/> a
<t>Version 6 PKESK (<xref target="v6-pkesk"/>)</t> nd <xref target="pkesk-x25519" format="counter"/>) -- MTI</t>
<t>Version 6 SKESK (<xref target="v6-skesk"/>)</t> </li>
<t>Features subpacket: add flag for SEIPDv2 (<xref target="features-subpac <li>
ket"/>)</t> <t>X448 (Sections <xref target="key-x448" format="counter"/> and <
<t>Subpacket: Preferred AEAD Ciphersuites (<xref target="preferred-v2-seip xref target="pkesk-x448" format="counter"/>)</t>
d"/>)</t> </li>
<t>Secret key encryption: AEAD "S2K usage octet" (<xref target="s2k-usage- <li>
octet"/> and <xref target="secret-key-packet-formats"/>)</t> <t>ECDH with Curve25519Legacy (<xref target="ec-curves"/>)</t>
</list></t> </li>
<t>Version 6 Keys and Signatures: <li>
<list style="symbols"> <t>ECDH with Brainpool curves (<xref target="ec-curves"/>)</t>
<t>Version 6 Public keys (<xref target="v6-pubkeys"/>)</t> </li>
<t>Version 6 Fingerprint and Key ID (<xref target="v6-key-id-fingerprint"/ </ul>
>)</t> </li>
<t>Version 6 Secret keys (<xref target="secret-key-packet-formats"/>)</t> <li>
<t>Version 6 Signatures (<xref target="version-four-and-six-sig"/>)</t> <t>AEAD Encryption:
<t>Version 6 One-Pass Signatures (<xref target="one-pass-sig"/>)</t> </t>
</list></t> <ul spacing="normal">
<t>Certificate (Transferable Public Key) Structure: <li>
<list style="symbols"> <t>V2 SEIPD (<xref target="version-two-seipd"/>)</t>
<t>Preferences subpackets in Direct Key Signatures (<xref target="self-sig </li>
s"/>)</t> <li>
<t>Self-verifying revocation certificate (<xref target="v6-revocation-cert <t>AEAD modes:
ificate"/>)</t> </t>
<t>User ID is explicitly optional (<xref target="v6-certificate-structures <ul spacing="normal">
"/>)</t> <li>
</list></t> <t>OCB mode (<xref target="aead-mode-ocb"/>) -- MTI</t>
<t>S2K: Argon2 (<xref target="s2k-argon2"/>)</t> </li>
<t>Subpacket: Intended Recipient Fingerprint (<xref target="intended-recipient <li>
-fingerprint"/>)</t> <t>EAX mode (<xref target="aead-mode-eax"/>)</t>
<t>Digest algorithms: SHA3-256 and SHA3-512 (<xref target="hash-algos"/>)</t> </li>
<t>Packet: Padding (<xref target="padding-packet"/>)</t> <li>
<t>Message structure: Packet Criticality (<xref target="packet-criticality"/>) <t>GCM mode (<xref target="aead-mode-gcm"/>)</t>
</t> </li>
<t>Deprecations: </ul>
<list style="symbols"> </li>
<t>Public Key Algorithms: <li>
<list style="symbols"> <t>V6 PKESK (<xref target="v6-pkesk"/>)</t>
<t>Avoid RSA weak keys (<xref target="rsa-notes"/>)</t> </li>
<t>Avoid DSA (<xref target="dsa-notes"/>)</t> <li>
<t>Avoid ElGamal (<xref target="elgamal-notes"/>, <xref target="pkesk- <t>V6 SKESK (<xref target="v6-skesk"/>)</t>
elgamal"/>)</t> </li>
<t>For Version 6 Keys: Avoid EdDSA25519Legacy, Curve25519Legacy (<xref <li>
target="ec-curves"/>)</t> <t>Features signature subpacket: add flag for v2 SEIPD (<xref targ
</list></t> et="features-subpacket"/>)</t>
<t>Digest Algorithms: </li>
<list style="symbols"> <li>
<t>Avoid MD5, SHA1, RIPEMD160 (<xref target="hash-algos"/>)</t> <t>Signature Subpacket: Preferred AEAD Ciphersuites (<xref target=
</list></t> "preferred-v2-seipd"/>)</t>
<t>Symmetric Key Algorithms: </li>
<list style="symbols"> <li>
<t>Avoid IDEA, TripleDES, CAST5 (<xref target="symmetric-algos"/>)</t> <t>Secret key encryption: AEAD "S2K usage octet" (Sections <xref t
</list></t> arget="s2k-usage-octet" format="counter"/> and <xref target="secret-key-packet-f
<t>S2K Specifier: ormats" format="counter"/>)</t>
<list style="symbols"> </li>
<t>Avoid Simple S2K (<xref target="s2k-simple"/>)</t> </ul>
</list></t> </li>
<t>Secret Key protections (a.k.a. S2K Usage): <li>
<list style="symbols"> <t>Version 6 Keys and Signatures:
<t>Avoid MalleableCFB (<xref target="secret-key-encryption"/>)</t> </t>
</list></t> <ul spacing="normal">
<t>Packet Types: <li>
<list style="symbols"> <t>Version 6 Public Keys (<xref target="v6-pubkeys"/>)</t>
<t>Avoid Symmetrically-Encrypted Data (<xref target="sed"/>, <xref tar </li>
get="ciphertext-malleability"/>)</t> <li>
</list></t> <t>Version 6 Fingerprint and Key ID (<xref target="v6-key-id-finge
<t>Literal Data packet metadata: rprint"/>)</t>
<list style="symbols"> </li>
<t>Avoid Filename and Date fields (<xref target="lit"/>)</t> <li>
<t>Avoid Special <spanx style="verb">_CONSOLE</spanx> "filename" (<xre <t>Version 6 Secret Keys (<xref target="secret-key-packet-formats"
f target="for-eyes-only"/>)</t> />)</t>
</list></t> </li>
<t>Packet Versions: <li>
<list style="symbols"> <t>Version 6 Signatures (<xref target="version-four-and-six-sig"/>
<t>Avoid Version 3 Public Keys (<xref target="v3-pubkeys"/>)</t> )</t>
<t>Avoid Version 3 Signatures (<xref target="signature-packet"/>)</t> </li>
</list></t> <li>
<t>Signature Types: <t>Version 6 One-Pass Signatures (<xref target="one-pass-sig"/>)</
<list style="symbols"> t>
<t>Avoid Reserved Signature Type ID 0xFF (<xref target="sigtype-reserv </li>
ed"/>, <xref target="sig-computation-notes"/>)</t> </ul>
</list></t> </li>
<t>Signature Subpackets: <li>
<list style="symbols"> <t>Certificate (Transferable Public Key) Structure:
<t>For Version 6 Signatures: Avoid Issuer Key ID (<xref target="issuer </t>
-keyid-subpacket"/>)</t> <ul spacing="normal">
<t>Avoid Revocation Key (<xref target="revocation-key"/>)</t> <li>
</list></t> <t>Preferences subpackets in Direct Key signatures (<xref target="
<t>ASCII Armor: self-sigs"/>)</t>
<list style="symbols"> </li>
<t>Ignore, do not emit CRC (<xref target="optional-crc24"/>)</t> <li>
<t>Do not emit "Version" armor header (<xref target="armor-header-key- <t>Self-verifying revocation certificate (<xref target="v6-revocat
version"/>)</t> ion-certificate"/>)</t>
</list></t> </li>
<t>Cleartext Signature Framework: <li>
<list style="symbols"> <t>User ID is explicitly optional (<xref target="v6-certificate-st
<t>Ignore, avoid emitting unnecessary Hash: headers (<xref target="arm ructures"/>)</t>
or-header-key-hash"/>)</t> </li>
<t>Reject CSF signatures with invalid Hash: headers (<xref target="arm </ul>
or-header-key-hash"/>) or any other Armor Header (<xref target="cleartext-struct </li>
ure"/>)</t> <li>
</list></t> <t>S2K: Argon2 (<xref target="s2k-argon2"/>)</t>
</list></t> </li>
</list></t> <li>
<t>Subpacket: Intended Recipient Fingerprint (<xref target="intended-r
<section anchor="terminology-changes"><name>Terminology Changes</name> ecipient-fingerprint"/>)</t>
</li>
<t>Note that some of the words used in previous revisions of the OpenPGP standar <li>
d have been improved in this document.</t> <t>Digest Algorithms: SHA3-256 and SHA3-512 (<xref target="hash-algos"
/>)</t>
<t>In previous revisions, the following terms were used:</t> </li>
<li>
<t><list style="symbols"> <t>Packet: Padding (<xref target="padding-packet"/>)</t>
<t>"Radix-64" was used to refer to OpenPGP's ASCII Armor base64 encoding (<xre </li>
f target="base64"/>).</t> <li>
<t>"Old packet format" was used to refer to the Legacy packet format (<xref ta <t>Message Structure: Packet Criticality (<xref target="packet-critica
rget="legacy-packet-format"/>) predating <xref target="RFC2440"/>.</t> lity"/>)</t>
<t>"New packet format" was used to refer to the OpenPGP packet format (<xref t </li>
arget="openpgp-packet-format"/>) introduced in <xref target="RFC2440"/>.</t> <li>
<t>"Certificate" was used ambiguously to mean multiple things. <t>Deprecations:
In this document, it is used to mean "Transferable Public Key" exclusively.</t> </t>
<t>"Preferred Symmetric Algorithms" was the old name for the "Preferred Symmet <ul spacing="normal">
ric Ciphers for v1 SEIPD" subpacket (<xref target="preferred-v1-seipd"/>)</t> <li>
<t>"Modification Detection Code" or "MDC" was originally described as a distin <t>Public Key Algorithms:
ct packet (packet type ID 19), and its corresponding flag in the Features subpac </t>
ket (<xref target="features-subpacket"/>) was known as "Modification Detection". <ul spacing="normal">
It is now described as an intrinsic part of v1 SEIPD (<xref target="version-one- <li>
seipd"/>), and the same corresponding flag is known as "Symmetrically Encrypted <t>Avoid RSA weak keys (<xref target="rsa-notes"/>)</t>
Integrity Protected Data packet version 1".</t> </li>
<t>"Packet Tag" was used to refer to the Packet Type ID (<xref target="packet- <li>
types"/>), or sometimes to the encoded Packet Type ID (<xref target="packet-head <t>Avoid DSA (<xref target="dsa-notes"/>)</t>
ers"/>).</t> </li>
</list></t> <li>
<t>Avoid ElGamal (Sections <xref target="elgamal-notes" format
</section> ="counter"/> and <xref target="pkesk-elgamal" format="counter"/>)</t>
</section> </li>
<section anchor="acknowledgements"><name>Acknowledgements</name> <li>
<t>For Version 6 Keys: Avoid EdDSA25519Legacy and Curve25519Le
<t>Thanks to the openpgp design team for working on this document to prepare it gacy (<xref target="ec-curves"/>)</t>
for working group consumption: Stephen Farrell, Daniel Kahn Gillmor, Daniel Huig </li>
ens, Jeffrey Lau, Yutaka Niibe, Justus Winter and Paul Wouters.</t> </ul>
</li>
<t>Thanks to Werner Koch for the early work on rfc4880bis and Andrey Jivsov for <li>
<xref target="RFC6637"/>.</t> <t>Digest Algorithms:
</t>
<t>This document also draws on much previous work from a number of other authors <ul spacing="normal">
, including: Derek Atkins, Charles Breed, Dave Del Torto, Marc Dyksterhouse, Gai <li>
l Haspert, Gene Hoffman, Paul Hoffman, Ben Laurie, Raph Levien, Colin Plumb, Wil <t>Avoid MD5, SHA1, and RIPEMD160 (<xref target="hash-algos"/>
l Price, David Shaw, William Stallings, Mark Weaver, and Philip R. Zimmermann.</ )</t>
t> </li>
</ul>
</section> </li>
<section anchor="errata-listing"><name>Errata addressed by this document</name> <li>
<t>Symmetric Key Algorithms:
<t>The following verified errata have been incorporated or are otherwise resolve </t>
d by this document:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t>Avoid IDEA, TripleDES, and CAST5 (<xref target="symmetric-a
<t><xref target="Errata-2199"/> - S2K hash/cipher octet correction</t> lgos"/>)</t>
<t><xref target="Errata-2200"/> - No implicit use of IDEA correction</t> </li>
<t><xref target="Errata-2206"/> - PKESK acronym expansion</t> </ul>
<t><xref target="Errata-2208"/> - Signature key owner clarification</t> </li>
<t><xref target="Errata-2214"/> - Signature hashing clarification</t> <li>
<t><xref target="Errata-2216"/> - Self signature applies to user ID correction <t>S2K Specifier:
</t> </t>
<t><xref target="Errata-2219"/> - Session key encryption storage clarification <ul spacing="normal">
</t> <li>
<t><xref target="Errata-2222"/> - Simple hash <bcp14>MUST</bcp14>/<bcp14>MAY</ <t>Avoid Simple S2K (<xref target="s2k-simple"/>)</t>
bcp14> clarification</t> </li>
<t><xref target="Errata-2226"/> - Native line endings <bcp14>SHOULD</bcp14> cl </ul>
arification</t> </li>
<t><xref target="Errata-2234"/> - Radix-64 / base64 clarification</t> <li>
<t><xref target="Errata-2235"/> - ASCII / UTF-8 collation sequence clarificati <t>Secret Key Protections (a.k.a.&nbsp;S2K Usage):
on</t> </t>
<t><xref target="Errata-2236"/> - Packet Composition is a sequence clarificati <ul spacing="normal">
on</t> <li>
<t><xref target="Errata-2238"/> - Subkey packets come after all User ID packet <t>Avoid MalleableCFB (<xref target="secret-key-encryption"/>)
s clarification</t> </t>
<t><xref target="Errata-2240"/> - Subkey removal clarification</t> </li>
<t><xref target="Errata-2242"/> - mL / emLen variable correction</t> </ul>
<t><xref target="Errata-2243"/> - CFB mode initialization vector (IV) clarific </li>
ation</t> <li>
<t><xref target="Errata-2270"/> - SHA-224 octet sequence correction</t> <t>Packet Types:
<t><xref target="Errata-2271"/> - Radix-64 correction</t> </t>
<t><xref target="Errata-3298"/> - Key revocation signatures correction</t> <ul spacing="normal">
<t><xref target="Errata-5491"/> - C code fix for CRC24_POLY define</t> <li>
<t><xref target="Errata-7545"/> - Armor Header colon hex fix</t> <t>Avoid Symmetrically Encrypted Data (Sections <xref target="
</list></t> sed" format="counter"/> and <xref target="ciphertext-malleability" format="count
er"/>)</t>
</section> </li>
</ul>
</li>
<li>
<t>Literal Data Packet Metadata:
</t>
<ul spacing="normal">
<li>
<t>Avoid Filename and Date fields (<xref target="lit"/>)</t>
</li>
<li>
<t>Avoid Special <tt>_CONSOLE</tt> "filename" (<xref target="f
or-eyes-only"/>)</t>
</li>
</ul>
</li>
<li>
<t>Packet Versions:
</t>
<ul spacing="normal">
<li>
<t>Avoid Version 3 Public Keys (<xref target="v3-pubkeys"/>)</
t>
</li>
<li>
<t>Avoid Version 3 Signatures (<xref target="signature-packet"
/>)</t>
</li>
</ul>
</li>
<li>
<t>Signature Types:
</t>
<ul spacing="normal">
<li>
<t>Avoid Reserved Signature Type ID 0xFF (Sections <xref targe
t="sigtype-reserved" format="counter"/> and <xref target="sig-computation-notes"
format="counter"/>)</t>
</li>
</ul>
</li>
<li>
<t>Signature Subpackets:
</t>
<ul spacing="normal">
<li>
<t>For Version 6 Signatures: Avoid Issuer Key ID (<xref target
="issuer-keyid-subpacket"/>)</t>
</li>
<li>
<t>Avoid Revocation Key (<xref target="revocation-key"/>)</t>
</li>
</ul>
</li>
<li>
<t>ASCII Armor:
</t>
<ul spacing="normal">
<li>
<t>Ignore; do not emit CRC (<xref target="optional-crc24"/>)</
t>
</li>
<li>
<t>Do not emit "Version" Armor Header (<xref target="armor-hea
der-key-version"/>)</t>
</li>
</ul>
</li>
<li>
<t>Cleartext Signature Framework:
</t>
<ul spacing="normal">
<li>
<t>Ignore; avoid emitting unnecessary Hash: headers (<xref tar
get="armor-header-key-hash"/>)</t>
</li>
<li>
<t>Reject Cleartext Signature Framework signatures with invali
d Hash: headers (<xref target="armor-header-key-hash"/>) or any other Armor Head
er (<xref target="cleartext-structure"/>)</t>
</li>
</ul>
</li>
</ul>
</li>
</ul>
<section anchor="terminology-changes">
<name>Terminology Changes</name>
<t>Note that some of the words used in previous versions of the OpenPGP
specification have been improved in this document.</t>
<t>In previous versions, the following terms were used:</t>
<ul spacing="normal">
<li>
<t>"Radix-64" was used to refer to OpenPGP's ASCII Armor base64 enco
ding (<xref target="base64"/>).</t>
</li>
<li>
<t>"Old packet format" was used to refer to the Legacy packet format
(<xref target="legacy-packet-format"/>) predating <xref target="RFC2440"/>.</t>
</li>
<li>
<t>"New packet format" was used to refer to the OpenPGP packet forma
t (<xref target="openpgp-packet-format"/>) introduced in <xref target="RFC2440"/
>.</t>
</li>
<li>
<t>"Certificate" was used ambiguously to mean multiple things.
In this document, it means "Transferable Public Key" exclusively.</t>
</li>
<li>
<t>"Preferred Symmetric Algorithms" was the old name for the "Prefer
red Symmetric Ciphers for v1 SEIPD" subpacket (<xref target="preferred-v1-seipd"
/>).</t>
</li>
<li>
<t>"Modification Detection Code" or "MDC" was originally described a
s a distinct packet (Packet Type ID 19), and its corresponding flag in the Featu
res signature subpacket (<xref target="features-subpacket"/>) was known as "Modi
fication Detection".
It is now described as an intrinsic part of v1 SEIPD (<xref target="version-one-
seipd"/>), and the same corresponding flag is known as "Version 1 Symmetrically
Encrypted and Integrity Protected Data packet".</t>
</li>
<li>
<t>"Packet Tag" was used to refer to the Packet Type ID (<xref targe
t="packet-types"/>) or sometimes to the encoded Packet Type ID (<xref target="pa
cket-headers"/>).</t>
</li>
</ul>
</section>
</section>
<section anchor="errata-listing">
<name>Errata Addressed by This Document</name>
<t>The following verified errata have been incorporated or are otherwise r
esolved by this document:</t>
<ul spacing="normal">
<li>
<t><xref target="Errata-2199"/> - S2K hash/cipher octet correction</t>
</li>
<li>
<t><xref target="Errata-2200"/> - No implicit use of IDEA correction</
t>
</li>
<li>
<t><xref target="Errata-2206"/> - PKESK acronym expansion</t>
</li>
<li>
<t><xref target="Errata-2208"/> - Signature key owner clarification</t
>
</li>
<li>
<t><xref target="Errata-2214"/> - Signature hashing clarification</t>
</li>
<li>
<t><xref target="Errata-2216"/> - Self-signature applies to user ID co
rrection</t>
</li>
<li>
<t><xref target="Errata-2219"/> - Session key encryption storage clari
fication</t>
</li>
<li>
<t><xref target="Errata-2222"/> - Simple hash <bcp14>MUST</bcp14>/<bcp
14>MAY</bcp14> clarification</t>
</li>
<li>
<t><xref target="Errata-2226"/> - Native line endings <bcp14>SHOULD</b
cp14> clarification</t>
</li>
<li>
<t><xref target="Errata-2234"/> - Radix-64/base64 clarification</t>
</li>
<li>
<t><xref target="Errata-2235"/> - ASCII/UTF-8 collation sequence clari
fication</t>
</li>
<li>
<t><xref target="Errata-2236"/> - Packet Composition is a sequence cla
rification</t>
</li>
<li>
<t><xref target="Errata-2238"/> - Subkey packets come after all User I
D packets clarification</t>
</li>
<li>
<t><xref target="Errata-2240"/> - Subkey removal clarification</t>
</li>
<li>
<t><xref target="Errata-2242"/> - mL/emLen variable correction</t>
</li>
<li>
<t><xref target="Errata-2243"/> - CFB mode initialization vector (IV)
clarification</t>
</li>
<li>
<t><xref target="Errata-2270"/> - SHA-224 octet sequence correction</t
>
</li>
<li>
<t><xref target="Errata-2271"/> - Radix-64 correction</t>
</li>
<li>
<t><xref target="Errata-3298"/> - Key Revocation signatures correction
</t>
</li>
<li>
<t><xref target="Errata-5491"/> - C code fix for CRC24_POLY define</t>
</li>
<li>
<t><xref target="Errata-7545"/> - Armor Header colon hex fix</t>
</li>
<li>
<t><xref target="Errata-7889"/> - Signature/certification correction</
t>
</li>
</ul>
</section>
<section anchor="acknowledgements" numbered="false">
<name>Acknowledgements</name>
<t>Thanks to the OpenPGP Design Team for working on this document and prep
aring it for working group consumption: <contact fullname="Stephen Farrell"/>, <
contact fullname="Daniel Kahn Gillmor"/>, <contact fullname="Daniel Huigens"/>,
<contact fullname="Jeffrey Lau"/>, <contact fullname="Yutaka Niibe"/>, <contact
fullname="Justus Winter"/>, and <contact fullname="Paul Wouters"/>.</t>
<t>Thanks to <contact fullname="Werner Koch"/> for the early work on rfc48
80bis and <contact fullname="Andrey Jivsov"/> for the work on <xref target="RFC6
637"/>.</t>
<t>This document also draws on much previous work from a number of other a
uthors including <contact fullname="Derek Atkins"/>, <contact fullname="Charles
Breed"/>, <contact fullname="Dave Del Torto"/>, <contact fullname="Marc Dyksterh
ouse"/>, <contact fullname="Gail Haspert"/>, <contact fullname="Gene Hoffman"/>,
<contact fullname="Paul Hoffman"/>, <contact fullname="Ben Laurie"/>, <contact
fullname="Raph Levien"/>, <contact fullname="Colin Plumb"/>, <contact fullname="
Will Price"/>, <contact fullname="Daphne Shaw"/>, <contact fullname="William Sta
llings"/>, <contact fullname="Mark Weaver"/>, and <contact fullname="Philip R. Z
immermann"/>.</t>
</section>
</back> </back>
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