wdiff rfc9261xml2.original.xml rfc9261.xml

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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-tls-exported-authenticator-15" category="std"> number="9261" submissionType="IETF"
category="std" consensus="true" obsoletes="" updates="" xml:lang="en" tocInclude="true"
sortRefs="true" symRefs="true" version="3">

  <!-- xml2rfc v2v3 conversion 3.12.6 -->
  <front>
    <title abbrev="TLS Exported Authenticator">Exported Authenticators in TLS</title>
    <seriesInfo name="RFC" value="9261"/>
    <author initials="N." surname="Sullivan" fullname="Nick Sullivan">
      <organization>Cloudflare Inc.</organization>
      <address>
        <email>nick@cloudflare.com</email>
      </address>
    </author>
    <date year="2022" month="March" day="04"/>

    <area>Security</area>
    <workgroup>TLS</workgroup>
    <keyword>Internet-Draft</keyword> month="July"/>

    <area>sec</area>
    <workgroup>tls</workgroup>

    <abstract>
      <t>This document describes a mechanism that builds on Transport Layer Security (TLS) or
Datagram Transport Layer Security (DTLS) and enables peers to
provide a proof of ownership of an identity, such as an X.509 certificate.  This proof can
be exported by one peer, transmitted out-of-band out of band to the other peer, and verified by the
receiving peer.</t>
    </abstract>
  </front>
  <middle>
    <section anchor="introduction" title="Introduction"> numbered="true" toc="default">
      <name>Introduction</name>
      <t>This document provides a way to authenticate one party of a Transport Layer
Security (TLS) or Datagram Transport Layer Security (DTLS) connection to its peer
using authentication messages created after the session
has been established.  This allows both the client and server to prove ownership
of additional identities at any time after the handshake has completed.  This
proof of authentication can be exported and transmitted out-of-band out of band from one
party to be validated by its peer.</t>
      <t>This mechanism provides two advantages over the authentication that TLS and DTLS natively
provide:</t>

<t><list style="hanging">
  <t hangText="multiple identities -">
      <dl newline="false" spacing="normal">
        <dt>multiple identities:</dt>
        <dd>
  Endpoints that are authoritative for multiple identities - identities, but that do not have a
single certificate that includes all of the identities - identities, can authenticate additional
	identities over a single connection.</t>
  <t hangText="spontaneous authentication -">
  Endpoints can authenticate after connection.</dd>

        <dt>spontaneous authentication:</dt>
        <dd>
After a connection is established, endpoints can authenticate in response to
events in a higher-layer protocol, as well as integrating protocol; they can also integrate more context (such as context from the application).</t>
</list></t> application).</dd>
      </dl>
      <t>Versions of TLS prior to TLS 1.3 used renegotiation as a way to enable
post-handshake client authentication given an existing TLS connection.
The mechanism described in this document may be used to replace the
post-handshake authentication functionality provided by renegotiation.
Unlike renegotiation, exported Exported Authenticator-based post-handshake
      authentication does not require any changes at the TLS layer.</t>

      <t>Post-handshake authentication is defined in section 4.6.3 of TLS 1.3 <xref target="RFC8446"/>, target="RFC8446" sectionFormat="of" section="4.6.2"/>, but it has the
disadvantage of requiring additional state to be stored as part of the TLS
state machine.  Furthermore, the authentication boundaries of TLS 1.3 post-handshake authentication align with TLS record boundaries,
which are often not aligned with the authentication boundaries of the
higher-layer protocol.  For example, multiplexed connection protocols
like HTTP/2 <xref target="RFC7540"/> target="RFC9113" format="default"/> do not have a notion of which TLS record
a given message is a part of.</t>
      <t>Exported Authenticators are meant to be used as a building block for
application protocols.  Mechanisms such as those required to advertise
support and handle authentication errors are not handled by TLS (or DTLS).</t>
      <t>The minimum version of TLS and DTLS required to implement the mechanisms
decribed
described in this document are TLS 1.2 <xref target="RFC6347"/> target="RFC5246" format="default"/> and DTLS 1.2 <xref target="RFC5246"/>.</t> target="RFC6347" format="default"/>.</t>
    </section>
<section anchor="conventions-and-terminology" title="Conventions numbered="true" toc="default">
      <name>Conventions and Terminology">

<t>The Terminology</name>
        <t>
    The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”,
“SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
    NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and
“OPTIONAL” "<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as
    described in BCP
14 BCP&nbsp;14 <xref target="RFC2119"/> <xref target="RFC8174"/>
    when, and only when, they appear in all capitals, as shown here.</t> here.
        </t>
      <t>This document uses terminology such as client, server, connection,
handshake, endpoint, and peer that are defined in section 1.1 of
<xref target="RFC8446"/>. target="RFC8446" sectionFormat="of" section="1.1"/>.  The term “initial connection” "initial connection" refers to the (D)TLS
connection from which the exported authenticator Exported Authenticator messages are derived.</t>
    </section>
    <section anchor="message-sequences" title="Message Sequences"> numbered="true" toc="default">
      <name>Message Sequences</name>
      <t>There are two types of messages defined in this document: Authenticator Requests authenticator requests and Authenticators. authenticators.  These can be combined in the following three sequences:</t>
      <t>Client Authentication</t>

<t><list style="symbols">
  <t>Server

      <ul spacing="normal">
        <li>Server generates Authenticator Request</t>
  <t>Client authenticator request</li>
        <li>Client generates Authenticator from Server’s Authenticator Request</t>
  <t>Server Server's authenticator request</li>
        <li>Server validates Client’s Authenticator</t>
</list></t> Client's authenticator</li>
      </ul>
      <t>Server Authentication</t>

<t><list style="symbols">
  <t>Client
      <ul spacing="normal">
        <li>Client generates Authenticator Request</t>
  <t>Server authenticator request</li>
        <li>Server generates Authenticator authenticator from Client’s Authenticator Request</t>
  <t>Client Client's authenticator request</li>
        <li>Client validates Server’s Authenticator</t>
</list></t> Server's authenticator</li>
      </ul>
      <t>Spontaneous Server Authentication</t>

<t><list style="symbols">
  <t>Server
      <ul spacing="normal">
        <li>Server generates Authenticator</t>
  <t>Client authenticator</li>
        <li>Client validates Server’s Authenticator</t>
</list></t> Server's authenticator</li>
      </ul>
    </section>
    <section anchor="authenticator-request" title="Authenticator Request"> numbered="true" toc="default">
      <name>Authenticator Request</name>
      <t>The authenticator request is a structured message that can be created by either
party of a (D)TLS connection using data exported from that connection.  It can
be transmitted to the other party of the (D)TLS connection at the application
layer.  The application layer application-layer protocol used to send the authenticator request
SHOULD
<bcp14>SHOULD</bcp14> use a secure transport channel with equivalent security to TLS, such as QUIC <xref target="RFC9001"/>, target="RFC9001" format="default"/>, as its
underlying transport to keep the request confidential.  The
application MAY <bcp14>MAY</bcp14> use the existing (D)TLS connection to transport the authenticator.</t>
      <t>An authenticator request message can be constructed by either the client or the
server.  Server-generated authenticator requests use the CertificateRequest
message from Section 4.3.2 of <xref target="RFC8446"/>. target="RFC8446" sectionFormat="of" section="4.3.2"/>.  Client-generated
authenticator requests use a new message, called the ClientCertificateRequest,
which "ClientCertificateRequest",
that uses the same structure as CertificateRequest.  (Note that the latter
is not a request for a client certificate, but rather a certificate request
generated by the client.)  These message
structures are used even if the connection protocol is TLS 1.2 or DTLS 1.2.</t>
      <t>The CertificateRequest and ClientCertificateRequest messages are used to define the
parameters in a request for an authenticator.  These are encoded as TLS handshake messages, including
length and type fields. They do not include any TLS record layer record-layer framing and are not encrypted with a handshake or application-data key.</t>
      <t>The structures are defined to be:</t>

<figure><artwork><![CDATA[
      <artwork name="" type="" align="left" alt=""><![CDATA[
   struct {
      opaque certificate_request_context<0..2^8-1>;
      Extension extensions<2..2^16-1>;
   } ClientCertificateRequest;

   struct {
      opaque certificate_request_context<0..2^8-1>;
      Extension extensions<2..2^16-1>;
   } CertificateRequest;
]]></artwork></figure>

<t><list style="hanging">
  <t hangText="certificate_request_context:">
]]></artwork>
      <dl newline="false" spacing="normal">
        <dt>certificate_request_context:</dt>
        <dd>
  An opaque string which that identifies the authenticator request and which that will
be echoed in the authenticator message.  A certificate_request_context value MUST <bcp14>MUST</bcp14> be unique for
each authenticator request within the scope of a connection
(preventing replay and context confusion).  The
certificate_request_context SHOULD <bcp14>SHOULD</bcp14> be chosen to be unpredictable
to the peer (e.g., by randomly generating it) in order to prevent
an attacker who has temporary access to the peer’s peer's private key
from pre-computing precomputing valid authenticators.  For example, the application
may choose this value to correspond to a value used in an existing
datastructure
data structure in the software to simplify implementation.</t>
  <t hangText="extensions:"> implementation.</dd>
        <dt>extensions:</dt>
        <dd>
  The set of extensions allowed in the structures of CertificateRequest
structure
 and the ClientCertificateRequest structure are is comprised of those
defined in the TLS "TLS ExtensionType Values Values" IANA registry <xref target="RFC8447"/> containing CR in the TLS 1.3 column. "TLS 1.3" column (see <xref target="IANA-TLS" format='default' /> and <xref target="RFC8447" format="default"/>).  In addition, the set of
extensions in the ClientCertificateRequest structure MAY <bcp14>MAY</bcp14>
include the server_name extension <xref target="RFC6066"/> extension.</t>
</list></t> target="RFC6066" format="default"/>.</dd>
      </dl>

      <t>The uniqueness requirements of the certificate_request_context apply
only to
across CertificateRequest and ClientCertificateRequest messages that
are used as part of authenticator requests, but do apply across CertificateRequest
and ClientCertificateRequest messages. requests. A certificate_request_context value used
in a ClientCertificateRequest cannot be used in an authenticator
CertificateRequest on the same connection, and vice versa.  There is no impact
if the value
of a certificate_request_context used in an authenticator
request matches the value of a certificate_request_context in the handshake or
in a post-handshake message.</t>
    </section>
    <section anchor="authenticator" title="Authenticator"> numbered="true" toc="default">
      <name>Authenticator</name>
      <t>The authenticator is a structured message that can be exported from either
party of a (D)TLS connection.  It can be transmitted to the other party of
the (D)TLS connection at the application layer.  The application layer application-layer protocol used to send the authenticator
SHOULD
<bcp14>SHOULD</bcp14> use a secure transport channel with equivalent security to TLS, such as QUIC <xref target="RFC9001"/>, target="RFC9001" format="default"/>, as its
underlying transport to keep the authenticator confidential.
The application MAY <bcp14>MAY</bcp14> use the existing (D)TLS connection to transport the authenticator.</t>
      <t>An authenticator message can be constructed by either the client or the
server given an established (D)TLS connection, connection; an identity, such as an X.509 certificate, certificate;
and a corresponding private key.  Clients MUST NOT <bcp14>MUST NOT</bcp14> send an authenticator
without a preceding authenticator request; for servers servers, an
authenticator request is optional.  For authenticators that do not correspond
to authenticator requests, the certificate_request_context is chosen by
the server.</t>
      <section anchor="authenticator-keys" title="Authenticator Keys"> numbered="true" toc="default">
        <name>Authenticator Keys</name>

        <t>Each authenticator is computed using a Handshake Context and Finished MAC (Message Authentication Code) Key
derived from the (D)TLS connection.  These values are derived using an exporter as
described in Section 4 of <xref target="RFC5705"/> target="RFC5705" sectionFormat="of" section="4"/> (for (D)TLS 1.2) or Section 7.5 of <xref target="RFC8446"/> target="RFC8446" sectionFormat="of" section="7.5"/> (for
(D)TLS 1.3).  For (D)TLS 1.3, the exporter_master_secret MUST <bcp14>MUST</bcp14> be used, not the
early_exporter_master_secret.  These values use different labels depending on the role of the
sender:</t>

<t><list style="symbols">
  <t>The
        <ul spacing="normal">
          <li>The Handshake Context is an exporter value that is derived using the label
“EXPORTER-client
"EXPORTER-client authenticator handshake context” context" or “EXPORTER-server "EXPORTER-server
authenticator handshake context” context" for authenticators sent by the client or
server respectively.</t>
  <t>The
server, respectively.</li>
          <li>The Finished MAC Key is an exporter value derived using the label
“EXPORTER-client
"EXPORTER-client authenticator finished key” key" or “EXPORTER-server "EXPORTER-server authenticator
finished key” key" for authenticators sent by the client or server respectively.</t>
</list></t> server, respectively.</li>
        </ul>
        <t>The context_value used for the exporter is empty (zero length) for all four
values.  There is no need to include additional context
information at this stage since because the application-supplied context
is included in the authenticator itself.  The length of the exported
value is equal to the length of the output of the hash function associated with the selected cipher suite ciphersuite (for TLS 1.3) or the hash function used
for the pseudorandom function (PRF) (for (D)TLS 1.2).  Exported authenticators Authenticators cannot be
used with (D)TLS 1.2 cipher suites ciphersuites that do not use the TLS PRF and with TLS 1.3 cipher suites ciphersuites that do not have an associated
hash function.  This hash is referred to as the authenticator hash.</t> "authenticator hash".</t>

<t>To avoid key synchronization attacks, Exported Authenticators MUST NOT <bcp14>MUST NOT</bcp14> be generated or
accepted on (D)TLS 1.2 connections that did not negotiate
the extended master secret extension <xref target="RFC7627"/>.</t> target="RFC7627" format="default"/>.</t>
      </section>
      <section anchor="authenticator-construction" title="Authenticator Construction"> numbered="true" toc="default">
        <name>Authenticator Construction</name>
        <t>An authenticator is formed from the concatenation of TLS 1.3 <xref target="RFC8446"/>
Certificate, CertificateVerify, and Finished messages. messages <xref target="RFC8446" format="default"/>. These messages are
encoded as TLS handshake messages, including length and type fields.
They do not include any TLS record layer record-layer framing and are not encrypted with a handshake or application-data key.</t>
        <t>If the peer populating the certificate_request_context field in an authenticator’s authenticator's Certificate message has already created or
correctly validated an authenticator with the same value, then no
authenticator should be constructed.  If there is no authenticator request,
the extensions are chosen from those presented in the (D)TLS handshake’s handshake's ClientHello.
Only servers can provide an authenticator without a corresponding request.</t>

        <t>ClientHello extensions are used to determine permissible extensions
in the server’s server's unsolicited Certificate message in order to follow the general model for
extensions in (D)TLS in which extensions can only be included
as part of a Certificate message if they were previously sent as
part of a CertificateRequest message or ClientHello message.  This ensures that the recipient
will be able to process such extensions.</t>
        <section anchor="certificate" title="Certificate"> numbered="true" toc="default">
          <name>Certificate</name>
          <t>The Certificate message contains the identity to be used for authentication, such as the
end-entity certificate and any supporting certificates in the chain. This structure is
defined in <xref target="RFC8446"/>, Section 4.4.2.</t> target="RFC8446" sectionFormat="of" section="4.4.2"/>.</t>
          <t>The Certificate message contains an opaque string called
certificate_request_context,
"certificate_request_context", which is extracted from the authenticator request request, if
present.  If no authenticator request is provided, the certificate_request_context
can be chosen arbitrarily but MUST arbitrarily; however, it <bcp14>MUST</bcp14> be unique within the scope of the connection
and be unpredictable to the peer.</t>
          <t>Certificates chosen in the Certificate message MUST <bcp14>MUST</bcp14> conform to the
requirements of a Certificate message in the negotiated version of (D)TLS.  In
particular, the entries of certificate_list MUST <bcp14>MUST</bcp14> be valid for the signature algorithms
indicated by the peer in the “signature_algorithms” "signature_algorithms" and “signature_algorithms_cert”
extension, "signature_algorithms_cert"
extensions, as described in Section 4.2.3 of <xref target="RFC8446"/> target="RFC8446" sectionFormat="of" section="4.2.3"/> for (D)TLS 1.3 or
from
in Sections 7.4.2 <xref target="RFC5246" section="7.4.2" sectionFormat="bare"/> and 7.4.6 <xref target="RFC5246" section="7.4.6" sectionFormat="bare"/> of <xref target="RFC5246"/> for (D)TLS 1.2.</t>
          <t>In addition to “signature_algorithms” "signature_algorithms" and “signature_algorithms_cert”, "signature_algorithms_cert",
the “server_name” "server_name" <xref target="RFC6066"/>, “certificate_authorities”
(Section 4.2.4. of <xref target="RFC8446"/>), and “oid_filters”
(Section 4.2.5. of <xref target="RFC8446"/>) target="RFC6066" format="default"/>, "certificate_authorities"
(<xref target="RFC8446" sectionFormat="of" section="4.2.4"/>), and "oid_filters"
(<xref target="RFC8446" sectionFormat="of" section="4.2.5"/>) extensions are used to guide certificate
selection.</t>
          <t>Only the X.509 certificate type defined in <xref target="RFC8446"/> target="RFC8446" format="default"/> is supported.
Alternative certificate formats such as <xref target="RFC7250"/> Raw Public Keys as described in <xref target="RFC7250" format="default"/> are
not supported in this version of the specification and their use in this context
has not yet been analysed.</t> analyzed.</t>
          <t>If an authenticator request was provided, the Certificate message MUST <bcp14>MUST</bcp14> contain
only extensions present in the authenticator request.  Otherwise, the
Certificate message MUST <bcp14>MUST</bcp14> contain only extensions present in the (D)TLS ClientHello.
Unrecognized extensions in the authenticator request MUST <bcp14>MUST</bcp14> be ignored.</t>
        </section>
        <section anchor="certificateverify" title="CertificateVerify"> numbered="true" toc="default">
          <name>CertificateVerify</name>
          <t>This message is used to provide explicit proof that an endpoint possesses the
private key corresponding to its identity.  The format of this message is taken from TLS 1.3:</t>

<figure><artwork><![CDATA[
          <artwork name="" type="" align="left" alt=""><![CDATA[
   struct {
      SignatureScheme algorithm;
      opaque signature<0..2^16-1>;
   } CertificateVerify;
]]></artwork></figure>
]]></artwork>
          <t>The algorithm field specifies the signature algorithm used (see Section 4.2.3 of <xref target="RFC8446"/> target="RFC8446" sectionFormat="of" section="4.2.3"/>
for the definition of this field).  The signature is a digital signature
using that algorithm.</t>
          <t>The signature scheme MUST <bcp14>MUST</bcp14> be a valid signature scheme for TLS 1.3. This
excludes all RSASSA-PKCS1-v1_5 algorithms and combinations of ECDSA Elliptic Curve Digital Signature Algorithm (ECDSA) and hash
algorithms that are not supported in TLS 1.3.</t>
          <t>If an authenticator request is present, the signature algorithm MUST <bcp14>MUST</bcp14> be chosen
from one of the signature schemes present in the “signature_algorithms”
extensino "signature_algorithms"
extension of the authenticator request.
Otherwise, with spontaneous server authentication, the signature algorithm used MUST <bcp14>MUST</bcp14> be chosen
from the “signature_algorithms” "signature_algorithms" sent by the peer in the ClientHello of the (D)TLS
handshake.  If there are no available signature algorithms, then no
authenticator should be constructed.</t>
<t>The signature is computed using the chosen signature scheme over the concatenation of:</t>

<t><list style="symbols">
  <t>A

          <ul spacing="normal">
            <li>a string that consists of octet 32 (0x20) repeated 64 times</t>
  <t>The times,</li>
            <li>the context string “Exported Authenticator” "Exported Authenticator" (which is not NUL-terminated)</t>
  <t>A NUL-terminated),</li>
            <li>a single 0 octet which that serves as the separator</t>
  <t>The separator, and</li>
            <li>the hashed authenticator transcript</t>
</list></t> transcript.</li>
          </ul>
          <t>The authenticator transcript is the hash of the concatenated Handshake Context,
authenticator request (if present), and Certificate message:</t>

<figure><artwork><![CDATA[
          <artwork name="" type="" align="left" alt=""><![CDATA[
Hash(Handshake Context || authenticator request || Certificate)
]]></artwork></figure>
]]></artwork>

          <t>Where Hash is the authenticator hash defined in section 4.1. <xref target="authenticator-keys"/>.  If the authenticator request
is not present, it is omitted from this construction, i.e., it is zero-length.</t>
          <t>If the party that generates the exported authenticator does so with a different
connection than the party that is validating it, then the Handshake Context will
not match, resulting in a CertificateVerify message that does not validate.
This includes situations in which the application data is sent via TLS-terminating
proxy.  Given a failed CertificateVerify validation, it may be helpful for
the application to confirm that both peers share the same connection
using a value derived from the connection secrets (such as the Handshake Context)
before taking a user-visible action.</t>
        </section>
        <section anchor="finished" title="Finished"> numbered="true" toc="default">
          <name>Finished</name>
          <t>An HMAC <xref target="HMAC"/> target="RFC2104" format="default"/> over the hashed authenticator transcript, which transcript is the
concatenation of the Handshake Context, authenticator request (if present),
Certificate, and CertificateVerify.  The HMAC is computed using the authenticator hash, using the Finished MAC Key as
a key.</t>

<figure><artwork><![CDATA[
          <artwork name="" type="" align="left" alt=""><![CDATA[
Finished = HMAC(Finished MAC Key, Hash(Handshake Context ||
     authenticator request || Certificate || CertificateVerify))
]]></artwork></figure>
]]></artwork>
        </section>
        <section anchor="authenticator-creation" title="Authenticator Creation"> numbered="true" toc="default">
          <name>Authenticator Creation</name>
          <t>An endpoint constructs an authenticator by serializing the Certificate, CertificateVerify, and Finished as TLS handshake messages and concatenating the octets:</t>

<figure><artwork><![CDATA[
          <artwork name="" type="" align="left" alt=""><![CDATA[
Certificate || CertificateVerify || Finished
]]></artwork></figure>
]]></artwork>

          <t>An authenticator is valid if the CertificateVerify message is correctly constructed given the authenticator request (if
used) and the Finished message matches the expected value.  When validating an authenticator, constant-time
comparisons SHOULD <bcp14>SHOULD</bcp14> be used for signature and MAC validation.</t>
        </section>
      </section>
    </section>
    <section anchor="empty-authenticator" title="Empty Authenticator"> numbered="true" toc="default">
      <name>Empty Authenticator</name>
      <t>If, given an authenticator request, the endpoint does not have an appropriate
identity or does not want to return one, it constructs an authenticated
refusal called an empty authenticator. "empty authenticator".  This is a Finished
message sent without a Certificate or CertificateVerify. This message is an
HMAC over the hashed authenticator transcript with a Certificate message
containing no CertificateEntries and the CertificateVerify message omitted.
The HMAC is computed using the authenticator hash, using the Finished MAC Key as a key.
This message is encoded as a TLS handshake message, including length and type field.
It does not include TLS record layer record-layer framing and is not encrypted with a handshake or application-data key.</t>

<figure><artwork><![CDATA[
      <artwork name="" type="" align="left" alt=""><![CDATA[
Finished = HMAC(Finished MAC Key, Hash(Handshake Context ||
     authenticator request || Certificate))
]]></artwork></figure>
]]></artwork>
    </section>
    <section anchor="api-considerations" title="API considerations"> numbered="true" toc="default">
      <name>API Considerations</name>
      <t>The creation and validation of both authenticator requests and authenticators
SHOULD
<bcp14>SHOULD</bcp14> be implemented inside the (D)TLS library even if it is possible to implement
it at the application layer.  (D)TLS implementations supporting the use of exported
authenticators SHOULD Exported
Authenticators <bcp14>SHOULD</bcp14> provide application programming interfaces by which clients
and servers may request and verify exported authenticator Exported Authenticator messages.</t>
      <t>Notwithstanding the success conditions described below, all APIs MUST <bcp14>MUST</bcp14> fail if:</t>

<t><list style="symbols">
  <t>the
      <ul spacing="normal">
        <li>the connection uses a (D)TLS version of 1.1 or earlier, or</t>
  <t>the or</li>
        <li>the connection is (D)TLS 1.2 and the extended master secret extension <xref target="RFC7627"/> target="RFC7627" format="default"/> was not
negotiated</t>
</list></t>
negotiated</li>
      </ul>
      <t>The following sections describe APIs that are considered necessary to
implement exported authenticators. Exported Authenticators.  These are informative only.</t>
      <section anchor="the-request-api" title="The “request” API"> numbered="true" toc="default">
        <name>The "request" API</name>
        <t>The “request” "request" API takes as input:</t>

<t><list style="symbols">
  <t>certificate_request_context
        <ul spacing="normal">
          <li>certificate_request_context (from 0 to 255 octets)</t>
  <t>set octets)</li>
          <li>the set of extensions to include (this MUST <bcp14>MUST</bcp14> include signature_algorithms) and the
contents thereof</t>
</list></t> thereof</li>
        </ul>
        <t>It returns an authenticator request, which is a sequence of octets
that comprises a CertificateRequest or ClientCertificateRequest message.</t>
      </section>
      <section anchor="the-get-context-api" title="The “get context” API"> numbered="true" toc="default">
        <name>The "get context" API</name>
        <t>The “get context” "get context" API takes as input:</t>

<t><list style="symbols">
  <t>authenticator
        <ul spacing="normal">
          <li>authenticator or authenticator request</t>
</list></t> request</li>
        </ul>
        <t>It returns the certificate_request_context.</t>
      </section>
      <section anchor="the-authenticate-api" title="The “authenticate” API"> numbered="true" toc="default">
        <name>The "authenticate" API</name>
        <t>The “authenticate” "authenticate" API takes as input:</t>

<t><list style="symbols">
  <t>a
        <ul spacing="normal">
          <li>a reference to the initial connection</t>
  <t>an connection</li>
          <li>an identity, such as a set of certificate chains and associated extensions
(OCSP <xref target="RFC6960"/>, target="RFC6960" format="default"/>, SCT <xref target="RFC6962"/>, etc.)</t>
  <t>a target="RFC6962" format="default"/> (obsoleted by <xref target="RFC9162"/>), etc.)</li>

          <li>a signer (either the private key associated with the identity, identity or the interface to perform private key operations) for each chain</t>
  <t>an chain</li>
          <li>an authenticator request or certificate_request_context (from 0 to 255 octets)</t>
</list></t> octets)</li>
        </ul>

        <t>It returns either the exported authenticator or an empty authenticator
as a sequence of octets.  It is recommended <bcp14>RECOMMENDED</bcp14> that
the logic for selecting the certificates and extensions to include
in the exporter is be implemented in the TLS library.  Implementing this
in the TLS library lets the implementer take advantage of existing
extension and certificate selection logic logic, and the implementer can more easily remember
which extensions were sent in the ClientHello.</t>
        <t>It is also possible to implement this API outside of the TLS library using
TLS exporters.  This may be preferable in cases where the application
does not have access to a TLS library with these APIs or when TLS is
handled independently of the application layer application-layer protocol.</t>
      </section>
      <section anchor="the-validate-api" title="The “validate” API"> numbered="true" toc="default">
        <name>The "validate" API</name>
        <t>The “validate” "validate" API takes as input:</t>

<t><list style="symbols">
  <t>a
        <ul spacing="normal">
          <li>a reference to the initial connection</t>
  <t>an connection</li>
          <li>an optional authenticator request</t>
  <t>an authenticator</t>
  <t>a request</li>
          <li>an authenticator</li>
          <li>a function for validating a certificate chain</t>
</list></t> chain</li>
        </ul>
        <t>It returns a status to indicate whether or not the authenticator is valid or not after
applying the function for validating the certificate chain to the chain
contained in the authenticator.  If validation is successful, it also returns
the identity, such as the certificate chain and its extensions.</t>
        <t>The API should return a failure if the certificate_request_context of the
authenticator was used in a different authenticator that was previously validated.
Well-formed empty authenticators are returned as invalid.</t>
        <t>When validating an authenticator, constant-time comparison should be used.</t>
      </section>
    </section>
    <section anchor="iana-considerations" title="IANA Considerations"> numbered="true" toc="default">
      <name>IANA Considerations</name>
      <section anchor="update-of-the-tls-extensiontype-registry" title="Update numbered="true" toc="default">
        <name>Update of the TLS ExtensionType Registry"> Registry</name>
        <t>IANA is requested to update has updated the entry for server_name(0) in the registry for "TLS ExtensionType Values" registry <xref target="IANA-TLS"/> (defined in <xref target="RFC8446"/>) target="RFC8446" format="default"/>) by replacing the value in the “TLS 1.3” "TLS 1.3"
column with the value “CH, "CH, EE, CR” CR" and adding listing this document in the “Reference” "Reference" column.</t>
        <t>IANA is has also requested to add added the following note to the registry:</t>
 <blockquote>       <t>The addition of the “CR” "CR" to the “TLS 1.3” "TLS 1.3" column for the server_name(0) extension only marks the extension as valid in a ClientCertificateRequest created as part of client-generated authenticator requests.</t> requests.</t></blockquote>
      </section>
      <section anchor="update-of-the-tls-exporter-labels-registry" title="Update numbered="true" toc="default">
        <name>Update of the TLS Exporter Labels Registry"> Registry</name>

        <t>IANA is requested to add has added the following entries to the registry for "TLS Exporter
Labels Labels" registry <xref target="IANA-EXPORT"/> (defined in <xref target="RFC5705"/>): “EXPORTER-client authenticator handshake context”,
“EXPORTER-server target="RFC5705" format="default"/>): "EXPORTER-client authenticator handshake context”, “EXPORTER-client context",
"EXPORTER-server authenticator handshake context”, “EXPORTER-client context",
"EXPORTER-client authenticator finished key” key" and “EXPORTER-server
"EXPORTER-server authenticator finished key” key" with “DTLS-OK” "DTLS-OK" and “Recommended” "Recommended" set to “Y” "Y" and
this document added to listed as the “Reference” column.</t> reference.</t>
      </section>
      <section anchor="update-of-the-tls-handshaketype-registry" title="Update numbered="true" toc="default">
        <name>Update of the TLS HandshakeType Registry"> Registry</name>

        <t>IANA is requested to add has added the following entry to the "TLS HandshakeType" registry for
HandshakeType <xref target="IANA-HANDSHAKE"/> (defined in <xref target="RFC8446"/>): “client_certificate_request” target="RFC8446" format="default"/>): "client_certificate_request" (17)
with “DTLS-OK” and “Recommended” "DTLS-OK" set to “Y” "Y" and this document added
to listed
as the “Reference” column with reference.  In addition, the following appears in the “Note” column:
“Used "Comment" column:</t>
<blockquote><t>Used in TLS versions prior to 1.3.”</t> 1.3.</t></blockquote>

      </section>
    </section>
    <section anchor="security" title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>The Certificate/Verify/Finished pattern intentionally looks like the
      TLS 1.3 pattern which that now has been analyzed several times. For example,
<xref target="SIGMAC"/> target="SIGMAC" format="default"/> presents a relevant framework for analysis, and section 10. of  <xref target="RFC8446"/> target="RFC8446" sectionFormat="of" section="E.1.6"/>
contains a conprehensive comprehensive set of references.</t>

      <t>Authenticators are independent and unidirectional.  There is no explicit state change
inside TLS when an authenticator is either created or validated.  The application in
possession of a validated authenticator can rely on any semantics associated with data
in the certificate_request_context.</t>

<t><list style="symbols">
  <t>This
      <ul spacing="normal">
        <li>This property makes it difficult to formally prove that a server is jointly authoritative
over multiple identities, rather than individually authoritative over each.</t>
  <t>There each.</li>
        <li>There is no indication in (D)TLS about which point in time an authenticator was
computed.  Any feedback about the time of creation or validation of the authenticator
should be tracked as part of the application layer application-layer semantics if required.</t>
</list></t> required.</li>
      </ul>
      <t>The signatures generated with this API cover the context string
“Exported Authenticator” and therefore
"Exported Authenticator"; therefore, they cannot be transplanted into other
protocols.</t>
      <t>In TLS 1.3 1.3, the client can not cannot explicitly learn from the TLS layer whether its
Finished message was accepted. Because the application traffic keys are not
dependent on the client’s client's final flight, receiving messages from the server
does not prove that the server received the client’s Finished. client's Finished message.
To avoid disagreement between the client and server
on the authentication status of EAs, Exported Authenticators, servers MUST <bcp14>MUST</bcp14> verify the client Finished message
before sending an EA or processing a received EA.</t>

</section>
<section anchor="ack" title="Acknowledgements">

<t>Comments on this proposal were provided by Martin Thomson.  Suggestions for
<xref target="security"/> were provided by Karthikeyan Bhargavan.</t> Exported Authenticator.</t>
    </section>
  </middle>
  <back>

    <references title='Normative References'>

<reference anchor='RFC8446' target='https://www.rfc-editor.org/info/rfc8446'>
<front>
<title>The Transport Layer Security (TLS) Protocol Version 1.3</title>
<author fullname='E. Rescorla' initials='E.' surname='Rescorla'><organization/></author>
<date month='August' year='2018'/>
<abstract><t>This document specifies version 1.3 of the Transport Layer Security (TLS) protocol.  TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery.</t><t>This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961.  This document also specifies new requirements for TLS 1.2 implementations.</t></abstract>
</front>
<seriesInfo name='RFC' value='8446'/>
<seriesInfo name='DOI' value='10.17487/RFC8446'/>
</reference>

<reference anchor='RFC6347' target='https://www.rfc-editor.org/info/rfc6347'>
<front>
<title>Datagram Transport Layer Security Version 1.2</title>
<author fullname='E. Rescorla' initials='E.' surname='Rescorla'><organization/></author>
<author fullname='N. Modadugu' initials='N.' surname='Modadugu'><organization/></author>
<date month='January' year='2012'/>
<abstract><t>This document specifies version 1.2 of the Datagram Transport Layer Security (DTLS) protocol.  The DTLS protocol provides communications privacy for datagram protocols.  The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery.  The DTLS protocol is based on the Transport Layer Security (TLS) protocol and provides equivalent security guarantees.  Datagram semantics of the underlying transport are preserved by the DTLS protocol.  This document updates DTLS 1.0 to work with TLS version 1.2.  [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='6347'/>
<seriesInfo name='DOI' value='10.17487/RFC6347'/>
</reference>

<reference anchor='RFC5246' target='https://www.rfc-editor.org/info/rfc5246'>
<front>
<title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
<author fullname='T. Dierks' initials='T.' surname='Dierks'><organization/></author>
<author fullname='E. Rescorla' initials='E.' surname='Rescorla'><organization/></author>
<date month='August' year='2008'/>
<abstract><t>This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol.  The TLS protocol provides communications security over the Internet.  The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery.  [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5246'/>
<seriesInfo name='DOI' value='10.17487/RFC5246'/>
</reference>

<reference anchor='RFC2119' target='https://www.rfc-editor.org/info/rfc2119'>
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author fullname='S. Bradner' initials='S.' surname='Bradner'><organization/></author>
<date month='March' year='1997'/>
<abstract><t>In many standards track documents several words are used to signify the requirements in the specification.  These words are often capitalized. This document defines these words as they should be interpreted in IETF documents.  This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='2119'/>
<seriesInfo name='DOI' value='10.17487/RFC2119'/>
</reference>

<reference anchor='RFC8174' target='https://www.rfc-editor.org/info/rfc8174'>
<front>
<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
<author fullname='B. Leiba' initials='B.' surname='Leiba'><organization/></author>
<date month='May' year='2017'/>
<abstract><t>RFC 2119 specifies common key words that may be used in protocol  specifications.  This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the  defined special meanings.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='8174'/>
<seriesInfo name='DOI' value='10.17487/RFC8174'/>
</reference>

<reference anchor='RFC8447' target='https://www.rfc-editor.org/info/rfc8447'>
<front>
<title>IANA Registry Updates for TLS and DTLS</title>
<author fullname='J. Salowey' initials='J.' surname='Salowey'><organization/></author>
<author fullname='S. Turner' initials='S.' surname='Turner'><organization/></author>
<date month='August' year='2018'/>
<abstract><t>This document describes a number of changes to TLS and DTLS IANA registries that range from adding notes to the registry all the way to changing the registration policy.  These changes were mostly motivated by WG review of the TLS- and DTLS-related registries undertaken as part of the TLS 1.3 development process.</t><t>This document updates the following RFCs: 3749, 5077, 4680, 5246, 5705, 5878, 6520, and 7301.</t></abstract>
</front>
<seriesInfo name='RFC' value='8447'/>
<seriesInfo name='DOI' value='10.17487/RFC8447'/>
</reference>

<reference anchor='RFC6066' target='https://www.rfc-editor.org/info/rfc6066'>
<front>
<title>Transport Layer Security (TLS) Extensions: Extension Definitions</title>
<author fullname='D. Eastlake 3rd' initials='D.' surname='Eastlake 3rd'><organization/></author>
<date month='January' year='2011'/>
<abstract><t>This document provides specifications for existing TLS extensions.  It is a companion document for RFC 5246, &quot;The Transport Layer Security (TLS) Protocol Version 1.2&quot;.  The extensions specified are server_name, max_fragment_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_request.  [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='6066'/>
<seriesInfo name='DOI' value='10.17487/RFC6066'/>
</reference>

<reference anchor='RFC5705' target='https://www.rfc-editor.org/info/rfc5705'>
<front>
<title>Keying Material Exporters for Transport Layer Security (TLS)</title>
<author fullname='E. Rescorla' initials='E.' surname='Rescorla'><organization/></author>
<date month='March' year='2010'/>
<abstract><t>A number of protocols wish to leverage Transport Layer Security (TLS) to perform key establishment but then use some of the keying material for their own purposes.  This document describes a general mechanism for allowing that.  [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5705'/>
<seriesInfo name='DOI' value='10.17487/RFC5705'/>
</reference>

<reference anchor='RFC7627' target='https://www.rfc-editor.org/info/rfc7627'>
<front>
<title>Transport Layer Security (TLS) Session Hash and Extended Master Secret Extension</title>
<author fullname='K. Bhargavan' initials='K.' role='editor' surname='Bhargavan'><organization/></author>
<author fullname='A. Delignat-Lavaud' initials='A.' surname='Delignat-Lavaud'><organization/></author>
<author fullname='A. Pironti' initials='A.' surname='Pironti'><organization/></author>
<author fullname='A. Langley' initials='A.' surname='Langley'><organization/></author>
<author fullname='M. Ray' initials='M.' surname='Ray'><organization/></author>
<date month='September' year='2015'/>
<abstract><t>The Transport Layer Security (TLS) master secret is not cryptographically bound to important session parameters such as the server certificate.  Consequently, it is possible for an active attacker to set up two sessions, one with a client and another with a server, such that the master secrets on the two sessions are the same.  Thereafter, any mechanism that relies on the master secret for authentication, including session resumption, becomes vulnerable to a man-in-the-middle attack, where the attacker can simply forward messages back and forth between the client and server.  This specification defines a TLS extension that contextually binds the master secret to a log of the full handshake that computes it, thus preventing such attacks.</t></abstract>
</front>
<seriesInfo name='RFC' value='7627'/>
<seriesInfo name='DOI' value='10.17487/RFC7627'/>
</reference>

<reference anchor='HMAC' target='https://www.rfc-editor.org/info/rfc2104'>
<front>
<title>HMAC: Keyed-Hashing for Message Authentication</title>
<author fullname='H. Krawczyk' initials='H.' surname='Krawczyk'><organization/></author>
<author fullname='M. Bellare' initials='M.' surname='Bellare'><organization/></author>
<author fullname='R. Canetti' initials='R.' surname='Canetti'><organization/></author>
<date month='February' year='1997'/>
<abstract><t>This document describes HMAC, a mechanism for message authentication using cryptographic hash functions. HMAC can be used with any iterative cryptographic hash function, e.g., MD5, SHA-1, in combination with a secret shared key.  The cryptographic strength of HMAC depends on the properties of the underlying hash function.  This memo provides information for the Internet community.  This memo does not specify an Internet standard of any kind</t></abstract>
</front>
<seriesInfo name='RFC' value='2104'/>
<seriesInfo name='DOI' value='10.17487/RFC2104'/>
</reference>

<displayreference target="RFC2104" to="HMAC"/>

    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8446.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6347.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5246.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8447.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6066.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5705.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7627.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2104.xml"/>
      </references>

    <references title='Informative References'>
      <references>
        <name>Informative References</name>

   <reference anchor="SIGMAC" target="https://eprint.iacr.org/2016/711.pdf">
	 <front>
	   <title>A Unilateral-to-Mutual Authentication Compiler for Key Exchange (with Applications to Client Authentication in TLS 1.3)</title>
	   <author initials="H." surname="Krawczyk">
      <organization></organization> initials="H" surname="Krawczyk" fullname="Hugo Krawczyk">
	     <organization/>
	   </author>
	   <date month="August" year="2016"/>
	 </front>
</reference>

<reference anchor='RFC7540' target='https://www.rfc-editor.org/info/rfc7540'>
<front>
<title>Hypertext Transfer Protocol Version 2 (HTTP/2)</title>
<author fullname='M. Belshe' initials='M.' surname='Belshe'><organization/></author>
<author fullname='R. Peon' initials='R.' surname='Peon'><organization/></author>
<author fullname='M. Thomson' initials='M.' role='editor' surname='Thomson'><organization/></author>
<date month='May' year='2015'/>
<abstract><t>This specification describes an optimized expression of the semantics
	 <refcontent>Proceedings of the Hypertext Transfer Protocol (HTTP), referred to as HTTP version 2 (HTTP/2).  HTTP/2 enables a more efficient use of network resources and a reduced perception of latency by introducing header field compression and allowing multiple concurrent exchanges 2016 ACM SIGSAC Conference on the same connection.  It also introduces unsolicited push of representations from servers to clients.</t><t>This specification is an alternative to, but does not obsolete, the HTTP/1.1 message syntax.  HTTP's existing semantics remain unchanged.</t></abstract>
</front>
<seriesInfo name='RFC' value='7540'/>
<seriesInfo name='DOI' value='10.17487/RFC7540'/>
</reference>

<reference anchor='RFC9001' target='https://www.rfc-editor.org/info/rfc9001'>
<front>
<title>Using TLS to Secure QUIC</title>
<author fullname='M. Thomson' initials='M.' role='editor' surname='Thomson'><organization/></author>
<author fullname='S. Turner' initials='S.' role='editor' surname='Turner'><organization/></author>
<date month='May' year='2021'/>
<abstract><t>This document describes how Transport Layer Security (TLS) is used to secure QUIC.</t></abstract>
</front>
<seriesInfo name='RFC' value='9001'/> Computer and Communications Security</refcontent>
	 <seriesInfo name='DOI' value='10.17487/RFC9001'/> name="DOI" value="10.1145/2976749.2978325"/>
</reference>

        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.9113.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.9001.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7250.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6960.xml"/>

	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6962.xml"/>

	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.9162.xml"/>

<reference anchor='RFC7250' target='https://www.rfc-editor.org/info/rfc7250'> anchor="IANA-TLS"
           target="https://www.iana.org/assignments/tls-extensiontype-values/">

  <front>
<title>Using Raw Public Keys in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)</title>
<author fullname='P. Wouters' initials='P.' role='editor' surname='Wouters'><organization/></author>
<author fullname='H. Tschofenig' initials='H.' role='editor' surname='Tschofenig'><organization/></author>
<author fullname='J. Gilmore' initials='J.' surname='Gilmore'><organization/></author>
<author fullname='S. Weiler' initials='S.' surname='Weiler'><organization/></author>
<author fullname='T. Kivinen' initials='T.' surname='Kivinen'><organization/></author>
<date month='June' year='2014'/>
<abstract><t>This document specifies a new certificate type and two TLS extensions for exchanging raw public keys in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS).  The new certificate type allows raw public keys to be used for authentication.</t></abstract>
    <title>TLS ExtensionType Values</title>
    <author><organization>IANA</organization></author>
  </front>
<seriesInfo name='RFC' value='7250'/>
<seriesInfo name='DOI' value='10.17487/RFC7250'/>
</reference>

<reference anchor='RFC6960' target='https://www.rfc-editor.org/info/rfc6960'> anchor="IANA-EXPORT"
           target="https://www.iana.org/assignments/tls-parameters/">
  <front>
<title>X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP</title>
<author fullname='S. Santesson' initials='S.' surname='Santesson'><organization/></author>
<author fullname='M. Myers' initials='M.' surname='Myers'><organization/></author>
<author fullname='R. Ankney' initials='R.' surname='Ankney'><organization/></author>
<author fullname='A. Malpani' initials='A.' surname='Malpani'><organization/></author>
<author fullname='S. Galperin' initials='S.' surname='Galperin'><organization/></author>
<author fullname='C. Adams' initials='C.' surname='Adams'><organization/></author>
<date month='June' year='2013'/>
<abstract><t>This document specifies a protocol useful in determining the current status of a digital certificate without requiring Certificate Revocation Lists (CRLs). Additional mechanisms addressing PKIX operational requirements are specified in separate documents.  This document obsoletes RFCs 2560 and 6277.  It also updates RFC 5912.</t></abstract>
    <title>TLS Exporter Labels</title>
    <author><organization>IANA</organization></author>
  </front>
<seriesInfo name='RFC' value='6960'/>
<seriesInfo name='DOI' value='10.17487/RFC6960'/>
</reference>

<reference anchor='RFC6962' target='https://www.rfc-editor.org/info/rfc6962'> anchor="IANA-HANDSHAKE"
           target="https://www.iana.org/assignments/tls-parameters/">
  <front>
<title>Certificate Transparency</title>
<author fullname='B. Laurie' initials='B.' surname='Laurie'><organization/></author>
<author fullname='A. Langley' initials='A.' surname='Langley'><organization/></author>
<author fullname='E. Kasper' initials='E.' surname='Kasper'><organization/></author>
<date month='June' year='2013'/>
<abstract><t>This document describes an experimental protocol for publicly logging the existence of Transport Layer Security (TLS) certificates as they are issued or observed, in a manner that allows anyone to audit certificate authority (CA) activity and notice the issuance of suspect certificates as well as to audit the certificate logs themselves.  The intent is that eventually clients would refuse to honor certificates that do not appear in a log, effectively forcing CAs to add all issued certificates to the logs.</t><t>Logs are network services that implement the protocol operations for submissions and queries that are defined in this document.</t></abstract>
    <title>TLS HandshakeType</title>
    <author><organization>IANA</organization></author>
  </front>
<seriesInfo name='RFC' value='6962'/>
<seriesInfo name='DOI' value='10.17487/RFC6962'/>
</reference>

      </references>
    </references>
    <section anchor="ack" numbered="false" toc="default">
      <name>Acknowledgements</name>
      <t>Comments on this proposal were provided by <contact fullname="Martin Thomson"/>.  Suggestions for
<xref target="security" format="default"/> were provided by <contact fullname="Karthikeyan Bhargavan"/>.</t>
    </section>

  </back>

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