Internet Engineering Task Force (IETF)                           R. Mahy
Request for Comments: 9734                Rohan Mahy Consulting Services
Category: Standards Track                                  February 2025
ISSN: 2070-1721


X.509 Certificate Extended Key Usage (EKU) for Instant Messaging URIs

Abstract

  RFC 5280 specifies several extended key purpose identifiers
  (KeyPurposeIds) for X.509 certificates.  This document defines an
  Instant Messaging (IM) identity KeyPurposeId for inclusion in the
  Extended Key Usage (EKU) extension of X.509 v3 public key
  certificates

Status of This Memo

  This is an Internet Standards Track document.

  This document is a product of the Internet Engineering Task Force
  (IETF).  It represents the consensus of the IETF community.  It has
  received public review and has been approved for publication by the
  Internet Engineering Steering Group (IESG).  Further information on
  Internet Standards is available in Section 2 of RFC 7841.

  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/rfc9734.

Copyright Notice

  Copyright (c) 2025 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 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.

Table of Contents

  1.  Introduction
  2.  Conventions and Definitions
  3.  The IM URI EKU
  4.  Security Considerations
  5.  IANA Considerations
  6.  References
    6.1.  Normative References
    6.2.  Informative References
  Appendix A.  ASN.1 Module
  Acknowledgments
  Author's Address

1.  Introduction

  Instant Messaging (IM) systems using the Messaging Layer Security
  (MLS) [RFC9420] protocol can incorporate per-client identity
  certificate credentials.  A subjectAltName in these certificates can
  be an IM URI [RFC3860] or Extensible Messaging and Presence Protocol
  (XMPP) URI [RFC6121], for example.

  Organizations may be unwilling to issue certificates for an IM client
  using a general KeyPurposeId, such as id-kp-serverAuth or id-kp-
  clientAuth, because of the risk that such certificates could be
  abused in a cross-protocol attack.

  An explanation of MLS credentials as they apply to IM is described in
  [E2E-IDENTITY].  These credentials are expected to be heavily used in
  the More Instant Messaging Interoperability (MIMI) Working Group.

2.  Conventions and Definitions

  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.

3.  The IM URI EKU

  This specification defines the KeyPurposeId id-kp-imUri, which may be
  included in certificates used to prove the identity of an IM client.
  This EKU extension MAY, at the option of the certificate issuer, be
  either critical or non-critical.

  id-kp  OBJECT IDENTIFIER  ::= {
    iso(1) identified-organization(3) dod(6) internet(1)
    security(5) mechanisms(5) pkix(7) kp(3) }

  id-kp-imUri OBJECT IDENTIFIER ::= { id-kp 40 }

4.  Security Considerations

  The security considerations of [RFC5280] are applicable to this
  document.  The id-kp-imUri extended key purpose does not introduce
  new security risks but instead reduces existing security risks by
  providing means to identify if the certificate is generated to sign
  IM identity credentials.  Issuers SHOULD NOT set the id-kp-imUri
  extended key purpose and an id-kp-clientAuth or id-kp-serverAuth
  extended key purpose: that would defeat the improved specificity
  offered by having an id-kp-imUri extended key purpose.

5.  IANA Considerations

  IANA has registered the following OID in the "SMI Security for PKIX
  Extended Key Purpose" registry (1.3.6.1.5.5.7.3).  This OID is
  defined in Section 3.

                 +=========+=============+============+
                 | Decimal | Description | References |
                 +=========+=============+============+
                 | 40      | id-kp-imUri | RFC 9734   |
                 +---------+-------------+------------+

                                Table 1

  IANA has also registered the following ASN.1 [ITU.X690.2021] module
  OID in the "SMI Security for PKIX Module Identifier" registry
  (1.3.6.1.5.5.7.0).  This OID is defined in Appendix A.

                +=========+===============+============+
                | Decimal | Description   | References |
                +=========+===============+============+
                | 113     | id-mod-im-eku | RFC 9734   |
                +---------+---------------+------------+

                                Table 2

6.  References

6.1.  Normative References

  [ITU.X680.2021]
             ITU-T, "Information Technology - Abstract Syntax Notation
             One (ASN.1): Specification of basic notation", ITU-T
             Recommendation X.680, ISO/IEC 8824-1:2021, February 2021,
             <https://www.itu.int/rec/T-REC-X.680>.

  [ITU.X690.2021]
             ITU-T, "Information Technology - ASN.1 encoding rules:
             Specification of Basic Encoding Rules (BER), Canonical
             Encoding Rules (CER) and Distinguished Encoding Rules
             (DER)", ITU-T Recommendation X.690, ISO/IEC 8825-1-2021,
             February 2021, <https://www.itu.int/rec/T-REC-X.690>.

  [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/info/rfc2119>.

  [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/info/rfc5280>.

  [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/info/rfc8174>.

6.2.  Informative References

  [E2E-IDENTITY]
             Barnes, R. and R. Mahy, "Identity for E2E-Secure
             Communications", Work in Progress, Internet-Draft, draft-
             barnes-mimi-identity-arch-02, 4 February 2025,
             <https://datatracker.ietf.org/doc/html/draft-barnes-mimi-
             identity-arch-02>.

  [RFC3860]  Peterson, J., "Common Profile for Instant Messaging
             (CPIM)", RFC 3860, DOI 10.17487/RFC3860, August 2004,
             <https://www.rfc-editor.org/info/rfc3860>.

  [RFC6121]  Saint-Andre, P., "Extensible Messaging and Presence
             Protocol (XMPP): Instant Messaging and Presence",
             RFC 6121, DOI 10.17487/RFC6121, March 2011,
             <https://www.rfc-editor.org/info/rfc6121>.

  [RFC9420]  Barnes, R., Beurdouche, B., Robert, R., Millican, J.,
             Omara, E., and K. Cohn-Gordon, "The Messaging Layer
             Security (MLS) Protocol", RFC 9420, DOI 10.17487/RFC9420,
             July 2023, <https://www.rfc-editor.org/info/rfc9420>.

Appendix A.  ASN.1 Module

  The following module adheres to ASN.1 specifications [ITU.X680.2021]
  and [ITU.X690.2021].

  <CODE BEGINS>

  IM-EKU
    { iso(1) identified-organization(3) dod(6) internet(1)
    security(5) mechanisms(5) pkix(7) id-mod(0)
    id-mod-im-eku (113) }

  DEFINITIONS IMPLICIT TAGS ::=
  BEGIN

  -- OID Arc

  id-kp OBJECT IDENTIFIER ::=
    { iso(1) identified-organization(3) dod(6) internet(1)
      security(5) mechanisms(5) pkix(7) kp(3) }

  -- Extended Key Usage Values

  id-kp-imUri OBJECT IDENTIFIER ::= { id-kp 40 }

  END

  <CODE ENDS>

Acknowledgments

  Thanks to Sean Turner and Russ Housley for reviews, suggestions,
  corrections, and encouragement.

Author's Address

  Rohan Mahy
  Rohan Mahy Consulting Services
  Email: [email protected]

You are viewing proxied material from gopher.meulie.net. The copyright of proxied material belongs to its original authors. Any comments or complaints in relation to proxied material should be directed to the original authors of the content concerned. Please see the disclaimer for more details.