Relying Party Handling of Resource Public Key Infrastructure (RPKI) Certificate Revocation List (CRL) Number Extensions
draft-ietf-sidrops-rpki-crl-numbers-00

SIDROPS                                                      J. Snijders
Internet-Draft                                                    Fastly
Updates: 6487 (if approved)                                  B. Maddison
Intended status: Standards Track                              Workonline
Expires: 14 March 2025                                        T. Buehler
                                                                 OpenBSD
                                                       10 September 2024

  Relying Party Handling of Resource Public Key Infrastructure (RPKI)
          Certificate Revocation List (CRL) Number Extensions
                 draft-ietf-sidrops-rpki-crl-numbers-00

Abstract

   This document clarifies how Resource Public Key Infrastructure (RPKI)
   Relying Parties (RPs) handle Certificate Revocation List (CRL) Number
   extensions.  This document updates RFC 6487.

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
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   This Internet-Draft will expire on 14 March 2025.

Copyright Notice

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

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   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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Related Work  . . . . . . . . . . . . . . . . . . . . . .   3
     1.3.  Changes from RFC 6487 . . . . . . . . . . . . . . . . . .   3
   2.  Updates to RFC 6487 . . . . . . . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     4.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Appendix A.  Implementation status - RFC EDITOR: REMOVE BEFORE
           PUBLICATION . . . . . . . . . . . . . . . . . . . . . . .   5
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Section 5.2.3 of [RFC5280] describes the value of the CRL Number
   extension as a monotonically increasing sequence number, which
   "allows users to easily determine when a particular CRL supersedes
   another CRL."  In other words, in PKIs in which it is possible for
   RPs to encounter multiple usable CRLs, the CRL Number extension is a
   means for the RP to determine which CRL(s) to rely upon.

   In the RPKI, a well-formed Manifest FileList contains exactly one
   entry for its associated CRL, together with a collision-resistant
   message digest of that CRLs contents (see Section 2.2 of [RFC6481]
   and Section 2 of [RFC9286]).  Additionally, the target of the CRL
   Distribution Points extension in an RPKI Resource Certificate is the
   same CRL object listed on the issuing CAs current manifest (see
   Section 4.8.6 of [RFC6487]).  Together, these properties guarantee
   that RPKI RPs will always be able to unambiguously identify exactly
   one current CRL for each RPKI CA.  Thus, in the RPKI, the ordering
   functionality provided by CRL Numbers is fully subsumed by
   monotonically increasing Manifest Numbers (Section 4.2.1 of
   [RFC9286]), thereby obviating the need for RPKI RPs to process CRL
   Number extensions at all.

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   Therefore, although the CRL Number extension is mandatory in RPKI
   CRLs for compliance with the X.509 v2 CRL Profile (Section 5 of
   [RFC5280]), any use of this extension by RPKI RPs merely adds
   complexity and fragility to RPKI Resource Certificate path
   validation.  This document mandates that RPKI RPs MUST ignore the CRL
   Number extension.

   This document updates [RFC6487] with clarifications for RP
   implementers.

1.1.  Requirements Language

   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.  Related Work

   It is assumed that the reader is familiar with the terms and concepts
   described in "Internet X.509 Public Key Infrastructure Certificate
   and Certificate Revocation List (CRL) Profile" [RFC5280] and "A
   Profile for Resource Certificate Repository Structure" [RFC6481].

1.3.  Changes from RFC 6487

   This section summarizes the significant changes between [RFC6487]
   this document.

   *  Clarifications for handling of CRL Numbers for RPs.

   *  Incorporated RFC 6487 Errata 3205.

2.  Updates to RFC 6487

   This section updates [RFC6487].

   *  In Section 5, this paragraph is removed.

      REMOVED

      |  Where two or more CRLs are issued by the same CA, the CRL with
      |  the highest value of the "CRL Number" field supersedes all
      |  other CRLs issued by this CA.

   *  In Section 5, this paragraph is changed.

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      OLD

      |  An RPKI CA MUST include the two extensions, Authority Key
      |  Identifier and CRL Number, in every CRL that it issues.  RPs
      |  MUST be prepared to process CRLs with these extensions.  No
      |  other CRL extensions are allowed.

      NEW

      |  An RPKI CA MUST include exactly two extensions in every CRL
      |  that it issues: an Authority Key Identifier (AKI) and a CRL
      |  Number.  No other CRL extensions are allowed.  RPs MUST process
      |  the AKI extension, and MUST ignore the CRL Number extension.

3.  IANA Considerations

   This document has no IANA actions.

4.  References

4.1.  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/info/rfc2119>.

   [RFC6481]  Huston, G., Loomans, R., and G. Michaelson, "A Profile for
              Resource Certificate Repository Structure", RFC 6481,
              DOI 10.17487/RFC6481, February 2012,
              <https://www.rfc-editor.org/info/rfc6481>.

   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487,
              DOI 10.17487/RFC6487, February 2012,
              <https://www.rfc-editor.org/info/rfc6487>.

   [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>.

   [RFC9286]  Austein, R., Huston, G., Kent, S., and M. Lepinski,
              "Manifests for the Resource Public Key Infrastructure
              (RPKI)", RFC 9286, DOI 10.17487/RFC9286, June 2022,
              <https://www.rfc-editor.org/info/rfc9286>.

4.2.  Informative References

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   [FORT]     Leiva, A., "FORT validator",
              <https://fortproject.net/en/validator>.

   [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>.

   [routinator]
              NLnetLabs, "Routinator",
              <https://github.com/NLnetLabs/routinator>.

   [rpki-client]
              Jeker, C., Snijders, J., Dzonsons, K., and T. Buehler,
              "rpki-client", June 2024, <https://www.rpki-client.org/>.

Appendix A.  Implementation status - RFC EDITOR: REMOVE BEFORE
             PUBLICATION

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in RFC 7942.
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to RFC 7942, "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

   The following RP implementations check for the presence of the CRL
   Number extension and whether it is marked non-critical, and otherwise
   ignore it.

   *  OpenBSD [rpki-client]

   *  [FORT]

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   *  [routinator] additionally checks that the CRL Number is non-
      negative and fits into 20 octets.

Acknowledgements

   The authors wish to thank Tom Harrison whose observations prompted
   this internet-draft proposal.

Authors' Addresses

   Job Snijders
   Fastly
   Amsterdam
   The Netherlands
   Email: job@fastly.com

   Ben Maddison
   Workonline
   Cape Town
   South Africa
   Email: benm@workonline.africa

   Theo Buehler
   OpenBSD
   Switzerland
   Email: tb@openbsd.org

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