Internet-Draft RPKI CRL Number handling for RPs May 2024
Snijders, et al. Expires 22 November 2024 [Page]
6487 (if approved)
Intended Status:
Standards Track
J. Snijders
B. Maddison
T. Buehler

Relying Party Handling of Resource Public Key Infrastructure (RPKI) Certificate Revocation List (CRL) Number Extensions


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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

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This Internet-Draft will expire on 22 November 2024.

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.

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.

1.3. 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.


    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.


    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.


    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

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Huston, G., Loomans, R., and G. Michaelson, "A Profile for Resource Certificate Repository Structure", RFC 6481, DOI 10.17487/RFC6481, , <>.
Huston, G., Michaelson, G., and R. Loomans, "A Profile for X.509 PKIX Resource Certificates", RFC 6487, DOI 10.17487/RFC6487, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Austein, R., Huston, G., Kent, S., and M. Lepinski, "Manifests for the Resource Public Key Infrastructure (RPKI)", RFC 9286, DOI 10.17487/RFC9286, , <>.

4.2. Informative References

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, , <>.


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

Authors' Addresses

Job Snijders
The Netherlands
Ben Maddison
Cape Town
South Africa
Theo Buehler