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