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Internationalization Updates to RFC 5280
draft-ietf-lamps-rfc8399bis-04

The information below is for an old version of the document.
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This is an older version of an Internet-Draft that was ultimately published as RFC 9549.
Author Russ Housley
Last updated 2024-01-18 (Latest revision 2024-01-17)
Replaces draft-housley-lamps-rfc8399bis
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Document shepherd Tim Hollebeek
Shepherd write-up Show Last changed 2023-12-12
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Responsible AD Roman Danyliw
Send notices to tim.hollebeek@digicert.com
IANA IANA review state IANA OK - No Actions Needed
draft-ietf-lamps-rfc8399bis-04
Network Working Group                                         R. Housley
Internet-Draft                                            Vigil Security
Obsoletes: 8399 (if approved)                            17 January 2024
Updates: 5280 (if approved)                                             
Intended status: Standards Track                                        
Expires: 20 July 2024

                Internationalization Updates to RFC 5280
                     draft-ietf-lamps-rfc8399bis-04

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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 20 July 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components

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   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Changes since RFC 8399  . . . . . . . . . . . . . . . . .   3
   2.  Updates to RFC 5280 . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Update in the Introduction (Section 1)  . . . . . . . . .   3
     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) . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   8
   References  . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     Normative References  . . . . . . . . . . . . . . . . . . . . .   8
     Informative References  . . . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

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].

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.

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

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     * 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

     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

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      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

   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.

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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

   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].

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   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

   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

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   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.

Acknowledgements

   Thanks to David Benjamin and Wei Chuang for identifying the issue and
   a solution.

   Thanks to Takahiro Nemoto, John Klensin, and Mike Ounsworth 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>.

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   [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>.

   [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>.

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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/>.

   [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>.

Author's Address

   Russ Housley
   Vigil Security, LLC
   Herndon, VA,
   United States of America
   Email: housley@vigilsec.com

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