rfc9549.original   rfc9549.txt 
Network Working Group R. Housley Internet Engineering Task Force (IETF) R. Housley
Internet-Draft Vigil Security Request for Comments: 9549 Vigil Security
Obsoletes: 8399 (if approved) 18 January 2024 Obsoletes: 8399 March 2024
Updates: 5280 (if approved) Updates: 5280
Intended status: Standards Track Category: Standards Track
Expires: 21 July 2024 ISSN: 2070-1721
Internationalization Updates to RFC 5280 Internationalization Updates to RFC 5280
draft-ietf-lamps-rfc8399bis-05
Abstract Abstract
The updates to RFC 5280 described in this document provide alignment The updates to RFC 5280 described in this document provide alignment
with the 2008 specification for Internationalized Domain Names (IDNs) with the 2008 specification for Internationalized Domain Names (IDNs)
and includes support for internationalized email addresses in X.509 and includes support for internationalized email addresses in X.509
certificates. The update ensures that name constraints for certificates. The updates ensure that name constraints for email
traditional email addresses and internationalized email addresses are addresses that contain only ASCII characters and internationalized
handled in the same manner. This document (once approved) obsoletes email addresses are handled in the same manner. This document
RFC 8399. obsoletes RFC 8399.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 21 July 2024. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9549.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology
1.2. Changes since RFC 8399 . . . . . . . . . . . . . . . . . 3 1.2. Changes since RFC 8399
2. Updates to RFC 5280 . . . . . . . . . . . . . . . . . . . . . 4 2. Updates to RFC 5280
2.1. Update in the Introduction (Section 1) . . . . . . . . . 4 2.1. Update in the Introduction (Section 1)
2.2. Update in Name Constraints (Section 4.2.1.10) . . . . . . 4 2.2. Update in Name Constraints (Section 4.2.1.10)
2.3. Update in IDNs in GeneralName (Section 7.2) . . . . . . . 5 2.3. Update in IDNs in GeneralName (Section 7.2)
2.4. Update in IDNs in Distinguished Names (Section 7.3) . . . 6 2.4. Update in IDNs in Distinguished Names (Section 7.3)
2.5. Update in Internationalized Electronic Mail Addresses 2.5. Update in Internationalized Electronic Mail Addresses
(Section 7.5) . . . . . . . . . . . . . . . . . . . . . . 7 (Section 7.5)
3. Security Considerations . . . . . . . . . . . . . . . . . . . 8 3. Security Considerations
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 4. IANA Considerations
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9 5. References
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5.1. Normative References
Normative References . . . . . . . . . . . . . . . . . . . . . 9 5.2. Informative References
Informative References . . . . . . . . . . . . . . . . . . . . 10 Acknowledgements
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 Author's Address
1. Introduction 1. Introduction
This document updates the Introduction in Section 1, the Name This document updates the Introduction in Section 1, the Name
Constraints certificate extension discussion in Section 4.2.1.10, and Constraints certificate extension discussion in Section 4.2.1.10, and
the Processing Rules for Internationalized Names in Section 7 of RFC the Processing Rules for Internationalized Names in Section 7 of RFC
5280 [RFC5280] to provide alignment with the 2008 specification for 5280 [RFC5280] to provide alignment with the 2008 specification for
Internationalized Domain Names (IDNs) and includes support for Internationalized Domain Names (IDNs) and includes support for
internationalized email addresses in X.509 certificates. internationalized email addresses in X.509 certificates.
skipping to change at page 3, line 19 skipping to change at line 105
The GeneralName structure supports many different name forms, The GeneralName structure supports many different name forms,
including otherName for extensibility. RFC 8398 [RFC8398] specifies including otherName for extensibility. RFC 8398 [RFC8398] specifies
the SmtpUTF8Mailbox for internationalized email addresses. the SmtpUTF8Mailbox for internationalized email addresses.
Note that Internationalized Domain Names in Applications Note that Internationalized Domain Names in Applications
specifications published in 2003 (IDNA2003) [RFC3490] and 2008 specifications published in 2003 (IDNA2003) [RFC3490] and 2008
(IDNA2008) [RFC5890] both refer to the Punycode algorithm for (IDNA2008) [RFC5890] both refer to the Punycode algorithm for
conversion [RFC3492]. conversion [RFC3492].
Note that characters in the Unicode Category “Symbol, Other” (So) are Note that characters in the Unicode Category "Symbol, Other" (So) are
specifically not included in IDNA2003 [RFC3490] or IDNA2008 specifically not included in IDNA2003 [RFC3490] or IDNA2008
[RFC5890]; the derived property values for character in this category [RFC5890]; the derived property values for characters in this
are calculated as DISALLOWED. Thus, some characters that are allowed category are calculated as DISALLOWED. Thus, some characters that
under the Unicode IDNA Compatibility Processing [UTS46] are not are allowed under the Unicode IDNA Compatibility Processing [UTS46]
allowed under this specification. For instance, ☕.example results in are not allowed under this specification. For instance, ♚.example,
in a failure under this specification, but it becomes xn--53h.example which contains the Unicode character U+1F0A1 (BLACK CHESS KING),
under [UTS46]. results in a failure under this specification, but it becomes
xn--45h.example under [UTS46].
1.1. Terminology 1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
1.2. Changes since RFC 8399 1.2. Changes since RFC 8399
In some cases, [RFC8399] required conversion of A-labels to U-labels In some cases, [RFC8399] required conversion of A-labels to U-labels
in order to process name constraints for internationalized email in order to process name constraints for internationalized email
addresses. This lead to implementation complexity and at least two addresses. This led to implementation complexity and at least two
security vulnerabilities. One summary of the vulnerabilities an be security vulnerabilities. One summary of the vulnerabilities can be
found in [DDHQ]. Now, all Internationalized Domain Names (IDNs) are found in [DDHQ]. Now, all IDNs are carried and processed as
carried and processed as A-labels. A-labels.
The Introduction provides a warning to implementers about the The Introduction provides a warning to implementers about the
handling of characters in the Unicode Category “Symbol, Other” (So), handling of characters in the Unicode Category "Symbol, Other" (So),
which includes emoji characters. which includes emoji characters.
2. Updates to RFC 5280 2. Updates to RFC 5280
This section provides updates to several paragraphs of [RFC5280]. This section provides updates to several paragraphs of [RFC5280].
For clarity, if the entire section is not replaced, then the original For clarity, if the entire section is not replaced, then the original
text and the replacement text are shown. text and the replacement text are shown.
2.1. Update in the Introduction (Section 1) 2.1. Update in the Introduction (Section 1)
This update provides references for IDNA2008. This update provides references for IDNA2008.
OLD OLD
* Enhanced support for internationalized names is specified in | * Enhanced support for internationalized names is specified in
Section 7, with rules for encoding and comparing | Section 7, with rules for encoding and comparing
Internationalized Domain Names, Internationalized Resource | Internationalized Domain Names, Internationalized Resource
Identifiers (IRIs), and distinguished names. These rules are | Identifiers (IRIs), and distinguished names. These rules are
aligned with comparison rules established in current RFCs, | aligned with comparison rules established in current RFCs,
including [RFC3490], [RFC3987], and [RFC4518]. | including [RFC3490], [RFC3987], and [RFC4518].
NEW NEW
* Enhanced support for internationalized names is specified in | * Enhanced support for internationalized names is specified in
Section 7, with rules for encoding and comparing | Section 7, with rules for encoding and comparing
Internationalized Domain Names, Internationalized Resource | Internationalized Domain Names, Internationalized Resource
Identifiers (IRIs), and distinguished names. These rules are | Identifiers (IRIs), and distinguished names. These rules are
aligned with comparison rules established in current RFCs, | aligned with comparison rules established in current RFCs,
including [RFC3987], [RFC4518], [RFC5890], and [RFC5891]. | including [RFC3987], [RFC4518], [RFC5890], and [RFC5891].
2.2. Update in Name Constraints (Section 4.2.1.10) 2.2. Update in Name Constraints (Section 4.2.1.10)
This update removes the ability to include constraints for a This update removes the ability to include constraints for a
particular mailbox. This capability was not used, and removing it particular mailbox. This capability was not used, and removing it
allows name constraints to apply to email addresses in rfc822Name and allows name constraints to apply to email addresses in rfc822Name and
SmtpUTF8Mailbox [RFC8398] within otherName. SmtpUTF8Mailbox [RFC8398] within otherName.
OLD OLD
A name constraint for Internet mail addresses MAY specify a
particular mailbox, all addresses at a particular host, or all | A name constraint for Internet mail addresses MAY specify a
mailboxes in a domain. To indicate a particular mailbox, the | particular mailbox, all addresses at a particular host, or all
constraint is the complete mail address. For example, | mailboxes in a domain. To indicate a particular mailbox, the
"root@example.com" indicates the root mailbox on the host | constraint is the complete mail address. For example,
"example.com". To indicate all Internet mail addresses on a | "root@example.com" indicates the root mailbox on the host
particular host, the constraint is specified as the host name. For | "example.com". To indicate all Internet mail addresses on a
example, the constraint "example.com" is satisfied by any mail | particular host, the constraint is specified as the host name.
address at the host "example.com". To specify any address within a | For example, the constraint "example.com" is satisfied by any mail
domain, the constraint is specified with a leading period (as with | address at the host "example.com". To specify any address within
URIs). For example, ".example.com" indicates all the Internet mail | a domain, the constraint is specified with a leading period (as
addresses in the domain "example.com", but not Internet mail | with URIs). For example, ".example.com" indicates all the
addresses on the host "example.com". | Internet mail addresses in the domain "example.com", but not
| Internet mail addresses on the host "example.com".
NEW NEW
A name constraint for Internet mail addresses MAY specify all | A name constraint for Internet mail addresses MAY specify all
addresses at a particular host or all mailboxes in a domain. To | addresses at a particular host or all mailboxes in a domain. To
indicate all Internet mail addresses on a particular host, the | indicate all Internet mail addresses on a particular host, the
constraint is specified as the host name. For example, the | constraint is specified as the host name. For example, the
constraint "example.com" is satisfied by any mail address at the | constraint "example.com" is satisfied by any mail address at the
host "example.com". To specify any address within a domain, the | host "example.com". To specify any address within a domain, the
constraint is specified with a leading period (as with URIs). For | constraint is specified with a leading period (as with URIs). For
example, ".example.com" indicates all the Internet mail addresses | example, ".example.com" indicates all the Internet mail addresses
in the domain "example.com" but not Internet mail addresses on | in the domain "example.com" but not Internet mail addresses on the
the host "example.com". | host "example.com".
2.3. Update in IDNs in GeneralName (Section 7.2) 2.3. Update in IDNs in GeneralName (Section 7.2)
This update aligns with IDNA2008. Since all of Section 7.2 is This update aligns with IDNA2008. Since all of Section 7.2 of
replaced, the OLD text is not provided. [RFC5280] is replaced, the OLD text is not provided.
NEW NEW
Internationalized Domain Names (IDNs) may be included in certificates
and CRLs in the subjectAltName and issuerAltName extensions, name
constraints extension, authority information access extension,
subject information access extension, CRL distribution points
extension, and issuing distribution point extension. Each of these
extensions uses the GeneralName type; one choice in GeneralName is
the dNSName field, which is defined as type IA5String.
IA5String is limited to the set of ASCII characters. To accommodate | Internationalized Domain Names (IDNs) may be included in
IDNs, U-labels are converted to A-labels. The A-label is the | certificates and CRLs in the subjectAltName and issuerAltName
encoding of the U-label according to the Punycode algorithm [RFC3492] | extensions, name constraints extension, authority information
with the ACE prefix "xn--" added at the beginning of the string. | access extension, subject information access extension, CRL
| distribution points extension, and issuing distribution point
When comparing DNS names for equality, conforming implementations | extension. Each of these extensions uses the GeneralName type;
MUST perform a case-insensitive exact match on the entire DNS name. | one choice in GeneralName is the dNSName field, which is defined
When evaluating name constraints, conforming implementations MUST | as type IA5String.
perform a case-insensitive exact match on a label-by-label basis. As |
noted in Section 4.2.1.10, any DNS name that may be constructed by | IA5String is limited to the set of ASCII characters. To
adding labels to the left-hand side of the domain name given as the | accommodate IDNs, U-labels are converted to A-labels. The A-label
constraint is considered to fall within the indicated subtree. | is the encoding of the U-label according to the Punycode algorithm
| [RFC3492] with the ACE prefix "xn--" added at the beginning of the
Implementations that have a user interface SHOULD convert IDNs to | string.
Unicode for display. Specifically, conforming implementations |
convert A-labels to U-labels for display purposes. | When comparing DNS names for equality, conforming implementations
| MUST perform a case-insensitive exact match on the entire DNS
Implementation consideration: There are increased memory requirements | name. When evaluating name constraints, conforming
for IDNs. An IDN ACE label will begin with the four additional | implementations MUST perform a case-insensitive exact match on a
characters "xn--", and an IDN can require as many as five ASCII | label-by-label basis. As noted in Section 4.2.1.10, any DNS name
characters to specify a single international character. | that may be constructed by adding labels to the left-hand side of
| the domain name given as the constraint is considered to fall
| within the indicated subtree.
|
| Implementations that have a user interface SHOULD convert IDNs to
| Unicode for display. Specifically, conforming implementations
| convert A-labels to U-labels for display purposes.
|
| Implementation consideration: There are increased memory
| requirements for IDNs. An IDN ACE label will begin with the four
| additional characters "xn--", and an IDN can require as many as
| five ASCII characters to specify a single international character.
2.4. Update in IDNs in Distinguished Names (Section 7.3) 2.4. Update in IDNs in Distinguished Names (Section 7.3)
This update aligns with IDNA2008. This update aligns with IDNA2008.
OLD OLD
Domain Names may also be represented as distinguished names using | Domain Names may also be represented as distinguished names using
domain components in the subject field, the issuer field, the | domain components in the subject field, the issuer field, the
subjectAltName extension, or the issuerAltName extension. As with | subjectAltName extension, or the issuerAltName extension. As with
the dNSName in the GeneralName type, the value of this attribute is | the dNSName in the GeneralName type, the value of this attribute
defined as an IA5String. Each domainComponent attribute represents a | is defined as an IA5String. Each domainComponent attribute
single label. To represent a label from an IDN in the distinguished | represents a single label. To represent a label from an IDN in
name, the implementation MUST perform the "ToASCII" label conversion | the distinguished name, the implementation MUST perform the
specified in Section 4.1 of RFC 3490. The label SHALL be considered | "ToASCII" label conversion specified in Section 4.1 of RFC 3490.
a "stored string". That is, the AllowUnassigned flag SHALL NOT be | The label SHALL be considered a "stored string". That is, the
set. | AllowUnassigned flag SHALL NOT be set.
NEW NEW
Domain names may also be represented as distinguished names using
domain components in the subject field, the issuer field, the | Domain names may also be represented as distinguished names using
subjectAltName extension, or the issuerAltName extension. As with | domain components in the subject field, the issuer field, the
the dNSName in the GeneralName type, the value of this attribute is | subjectAltName extension, or the issuerAltName extension. As with
defined as an IA5String. Each domainComponent attribute represents a | the dNSName in the GeneralName type, the value of this attribute
single label. To represent a label from an IDN in the distinguished | is defined as an IA5String. Each domainComponent attribute
name, the implementation MUST convert all U-labels to A-labels. | represents a single label. To represent a label from an IDN in
| the distinguished name, the implementation MUST convert all
| U-labels to A-labels.
2.5. Update in Internationalized Electronic Mail Addresses 2.5. Update in Internationalized Electronic Mail Addresses
(Section 7.5) (Section 7.5)
This update aligns with IDNA2008 and [RFC8398]. Since all of This update aligns with IDNA2008 and [RFC8398]. Since all of
Section 7.5 is replaced, the OLD text is not provided. Section 7.5 of [RFC5280] is replaced, the OLD text is not provided.
NEW NEW
Electronic Mail addresses may be included in certificates and CRLs in | Electronic Mail addresses may be included in certificates and CRLs
the subjectAltName and issuerAltName extensions, name constraints | in the subjectAltName and issuerAltName extensions, name
extension, authority information access extension, subject | constraints extension, authority information access extension,
information access extension, issuing distribution point extension, | subject information access extension, issuing distribution point
or CRL distribution points extension. Each of these extensions uses | extension, or CRL distribution points extension. Each of these
the GeneralName construct. If the email address includes an IDN but | extensions uses the GeneralName construct. If the email address
the local-part of the email address can be represented in ASCII, then | includes an IDN but the local-part of the email address can be
the email address is placed in the rfc822Name choice of GeneralName, | represented in ASCII, then the email address is placed in the
which is defined as type IA5String. If the local-part of the | rfc822Name choice of GeneralName, which is defined as type
internationalized email address cannot be represented in ASCII, then | IA5String. If the local-part of the internationalized email
the internationalized email address is placed in the otherName choice | address cannot be represented in ASCII, then the internationalized
of GeneralName using the conventions in RFC 8398 [RFC8398]. | email address is placed in the otherName choice of GeneralName
| using the conventions in RFC 8398 [RFC8398].
When the host-part contains an IDN, conforming implementations MUST |
convert all U-labels to A-labels. | When the host-part contains an IDN, conforming implementations
| MUST convert all U-labels to A-labels.
7.5.1. Local-Part Contains Only ASCII Characters |
| 7.5.1. Local-Part Contains Only ASCII Characters
Two email addresses are considered to match if: |
| Two email addresses are considered to match if:
1) The local-part of each name is an exact match, AND |
| 1) The local-part of each name is an exact match, AND
2) The host-part of each name matches using a case-insensitive |
ASCII comparison. | 2) The host-part of each name matches using a case-insensitive
| ASCII comparison.
Implementations that have a user interface SHOULD convert the |
host-part of internationalized email addresses specified in these | Implementations that have a user interface SHOULD convert the
extensions to Unicode before display. Specifically, conforming | host-part of internationalized email addresses specified in these
implementations convert A-labels to U-labels for display purposes. | extensions to Unicode before display. Specifically, conforming
| implementations convert A-labels to U-labels for display purposes.
7.5.2. Local-Part Contains Non-ASCII Characters |
When the local-part contains non-ASCII characters, conforming | 7.5.2. Local-Part Contains Non-ASCII Characters
implementations MUST place the internationalized email address in the |
SmtpUTF8Mailbox within the otherName choice of GeneralName as | When the local-part contains non-ASCII characters, conforming
specified in Section 3 of RFC 8398 [RFC8398]. Note that the UTF8 | implementations MUST place the internationalized email address in
encoding of the internationalized email address MUST NOT contain a | the SmtpUTF8Mailbox within the otherName choice of GeneralName as
Byte-Order-Mark (BOM) [RFC3629] to aid comparison. The email address | specified in Section 3 of RFC 8398 [RFC8398]. Note that the UTF8
local-part within the SmtpUTF8Mailbox MUST conform to the | encoding of the internationalized email address MUST NOT contain a
requirements of [RFC6530] and [RFC6531]. | Byte-Order-Mark (BOM) [RFC3629] to aid comparison. The email
| address local-part within the SmtpUTF8Mailbox MUST conform to the
Two email addresses are considered to match if: | requirements of [RFC6530] and [RFC6531].
|
1) The local-part of each name is an exact match, AND | Two email addresses are considered to match if:
|
2) The host-part of each name matches using a case-insensitive | 1) The local-part of each name is an exact match, AND
ASCII comparison. |
| 2) The host-part of each name matches using a case-insensitive
Implementations that have a user interface SHOULD convert the | ASCII comparison.
host-part of internationalized email addresses specified in these |
extensions to Unicode before display. Specifically, conforming | Implementations that have a user interface SHOULD convert the
implementations convert A-labels to U-labels for display purposes. | host-part of internationalized email addresses specified in these
| extensions to Unicode before display. Specifically, conforming
| implementations convert A-labels to U-labels for display purposes.
3. Security Considerations 3. Security Considerations
The Security Consideration related to IDNA2008 in Section 4 of The Security Considerations related to internationalized names in
[RFC5890] are relevant to this specification. Section 4 of [RFC5890] are relevant to this specification.
Conforming CAs SHOULD ensure that IDNs are valid according to Conforming Certification Authorities (CAs) SHOULD ensure that IDNs
IDNA2008, which is defined in [RFC5890], [RFC5891], [RFC5892], are valid according to IDNA2008, which is defined in [RFC5890],
[RFC5893], [RFC5894], and the updates to these documents. Failure to [RFC5891], [RFC5892], [RFC5893], [RFC5894], and the updates to these
use valid A-labels may yield a domain name that cannot be correctly documents. Failure to use valid A-labels may yield a domain name
represented in the Domain Name System (DNS). In addition, the CA/ that cannot be correctly represented in the Domain Name System (DNS).
Browser Forum offers some guidance regarding internal server names in In addition, the CA/Browser Forum offers some guidance regarding
certificates [CABF]. internal server names in certificates [CABF].
An earlier version of this specification [RFC8399] required An earlier version of this specification [RFC8399] required
conversion of A-labels to U-labels in order to process name conversion of A-labels to U-labels in order to process name
constraints for internationalized email addresses in SmtpUTF8Mailbox constraints for internationalized email addresses in SmtpUTF8Mailbox
other names. This lead to implementation complexity and at least two other names. This lead to implementation complexity and at least two
security vulnerabilities. Now, all Internationalized Domain Names security vulnerabilities. Now, all IDNs are carried and processed as
(IDNs) are carried and processed as A-labels. A-labels.
4. IANA Considerations 4. IANA Considerations
This document has no IANA actions. This document has no IANA actions.
Acknowledgements 5. References
Thanks to David Benjamin and Wei Chuang for identifying the issue and
a solution.
Thanks to Takahiro Nemoto, John Klensin, Mike Ounsworth, and Orie
Steele for their careful review and thoughtful comments.
References
Normative References 5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in Applications for Internationalized Domain Names in Applications
(IDNA)", RFC 3492, DOI 10.17487/RFC3492, March 2003, (IDNA)", RFC 3492, DOI 10.17487/RFC3492, March 2003,
<https://www.rfc-editor.org/rfc/rfc3492>. <https://www.rfc-editor.org/info/rfc3492>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/rfc/rfc3629>. 2003, <https://www.rfc-editor.org/info/rfc3629>.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987, Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
January 2005, <https://www.rfc-editor.org/rfc/rfc3987>. January 2005, <https://www.rfc-editor.org/info/rfc3987>.
[RFC4518] Zeilenga, K., "Lightweight Directory Access Protocol [RFC4518] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): Internationalized String Preparation", RFC 4518, (LDAP): Internationalized String Preparation", RFC 4518,
DOI 10.17487/RFC4518, June 2006, DOI 10.17487/RFC4518, June 2006,
<https://www.rfc-editor.org/rfc/rfc4518>. <https://www.rfc-editor.org/info/rfc4518>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/rfc/rfc5280>. <https://www.rfc-editor.org/info/rfc5280>.
[RFC5890] Klensin, J., "Internationalized Domain Names for [RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework", Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010, RFC 5890, DOI 10.17487/RFC5890, August 2010,
<https://www.rfc-editor.org/rfc/rfc5890>. <https://www.rfc-editor.org/info/rfc5890>.
[RFC5891] Klensin, J., "Internationalized Domain Names in [RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891, Applications (IDNA): Protocol", RFC 5891,
DOI 10.17487/RFC5891, August 2010, DOI 10.17487/RFC5891, August 2010,
<https://www.rfc-editor.org/rfc/rfc5891>. <https://www.rfc-editor.org/info/rfc5891>.
[RFC5892] Faltstrom, P., Ed., "The Unicode Code Points and [RFC5892] Faltstrom, P., Ed., "The Unicode Code Points and
Internationalized Domain Names for Applications (IDNA)", Internationalized Domain Names for Applications (IDNA)",
RFC 5892, DOI 10.17487/RFC5892, August 2010, RFC 5892, DOI 10.17487/RFC5892, August 2010,
<https://www.rfc-editor.org/rfc/rfc5892>. <https://www.rfc-editor.org/info/rfc5892>.
[RFC5893] Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts [RFC5893] Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts
for Internationalized Domain Names for Applications for Internationalized Domain Names for Applications
(IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010, (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010,
<https://www.rfc-editor.org/rfc/rfc5893>. <https://www.rfc-editor.org/info/rfc5893>.
[RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for [RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for
Internationalized Email", RFC 6530, DOI 10.17487/RFC6530, Internationalized Email", RFC 6530, DOI 10.17487/RFC6530,
February 2012, <https://www.rfc-editor.org/rfc/rfc6530>. February 2012, <https://www.rfc-editor.org/info/rfc6530>.
[RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized [RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized
Email", RFC 6531, DOI 10.17487/RFC6531, February 2012, Email", RFC 6531, DOI 10.17487/RFC6531, February 2012,
<https://www.rfc-editor.org/rfc/rfc6531>. <https://www.rfc-editor.org/info/rfc6531>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8398] Melnikov, A., Ed. and W. Chuang, Ed., "Internationalized [RFC8398] Melnikov, A., Ed. and W. Chuang, Ed., "Internationalized
Email Addresses in X.509 Certificates", RFC 8398, Email Addresses in X.509 Certificates", RFC 8398,
DOI 10.17487/RFC8398, May 2018, DOI 10.17487/RFC8398, May 2018,
<https://www.rfc-editor.org/rfc/rfc8398>. <https://www.rfc-editor.org/info/rfc8398>.
Informative References 5.2. Informative References
[CABF] CA/Browser Forum, "Internal Server Names and IP Address [CABF] CA/Browser Forum, "Internal Server Names and IP Address
Requirements for SSL: Guidance on the Deprecation of Requirements for SSL: Guidance on the Deprecation of
Internal Server Names and Reserved IP Addresses provided Internal Server Names and Reserved IP Addresses provided
by the CA/Browser Forum", Version 1.0, June 2012, by the CA/Browser Forum", Version 1.0, June 2012,
<https://cabforum.org/internal-names/>. <https://cabforum.org/internal-names/>.
[DDHQ] Datadog Security Labs, "The OpenSSL punycode vulnerability [DDHQ] Datadog Security Labs, "The OpenSSL punycode vulnerability
(CVE-2022-3602): Overview, detection, exploitation, and (CVE-2022-3602): Overview, detection, exploitation, and
remediation", 1 November 2022, remediation", 1 November 2022,
<https://securitylabs.datadoghq.com/articles/openssl- <https://securitylabs.datadoghq.com/articles/openssl-
november-1-vulnerabilities/>. november-1-vulnerabilities/>.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)", "Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, DOI 10.17487/RFC3490, March 2003, RFC 3490, DOI 10.17487/RFC3490, March 2003,
<https://www.rfc-editor.org/rfc/rfc3490>. <https://www.rfc-editor.org/info/rfc3490>.
[RFC5894] Klensin, J., "Internationalized Domain Names for [RFC5894] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Background, Explanation, and Applications (IDNA): Background, Explanation, and
Rationale", RFC 5894, DOI 10.17487/RFC5894, August 2010, Rationale", RFC 5894, DOI 10.17487/RFC5894, August 2010,
<https://www.rfc-editor.org/rfc/rfc5894>. <https://www.rfc-editor.org/info/rfc5894>.
[RFC8399] Housley, R., "Internationalization Updates to RFC 5280", [RFC8399] Housley, R., "Internationalization Updates to RFC 5280",
RFC 8399, DOI 10.17487/RFC8399, May 2018, RFC 8399, DOI 10.17487/RFC8399, May 2018,
<https://www.rfc-editor.org/rfc/rfc8399>. <https://www.rfc-editor.org/info/rfc8399>.
[UTS46] Davis, M. and M. Suignard, "Unicode Technical Standard [UTS46] Davis, M. and M. Suignard, "Unicode Technical Standard
#46: Unicode IDNA Compatibility Processing", Revision 31, #46: Unicode IDNA Compatibility Processing", Revision 31,
The Unicode Consortium, Mountain View, September 2023, The Unicode Consortium, Mountain View, September 2023,
<https://www.unicode.org/reports/tr46>. <https://www.unicode.org/reports/tr46>.
Acknowledgements
Thanks to David Benjamin and Wei Chuang for identifying the issue and
a solution.
Thanks to Takahiro Nemoto, John Klensin, Mike Ounsworth, and Orie
Steele for their careful review and thoughtful comments.
Author's Address Author's Address
Russ Housley Russ Housley
Vigil Security, LLC Vigil Security, LLC
Herndon, VA, Herndon, VA
United States of America United States of America
Email: housley@vigilsec.com Email: housley@vigilsec.com
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