RFC 9829: Handling of Resource Public Key Infrastructure (RPKI) Certificate Revocation List (CRL) Number Extensions

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/rfc9829.¶

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1. Introduction

Section 5.2.3 of [RFC5280] describes the value of the Certificate Revocation List (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 Public Key Infrastructures (PKIs) in which it is possible for Relying Parties (RPs) to encounter multiple usable CRLs, the CRL Number extension is a means for an RP to determine which CRLs to rely upon.¶

In the Resource Public Key Infrastructure (RPKI), a well-formed manifest fileList contains exactly one entry for its associated CRL, together with a collision-resistant message digest of that CRL's 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 Certification Authorities (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 ignore the CRL Number extension.¶

This document updates [RFC6487]. Refer to Section 3 for more details.¶

3. Updates to RFC 6487

4. Operational Considerations

This document has no additional operational considerations beyond those described in Section 9 of [RFC6487].¶

5. Security Considerations

The Security Considerations of [RFC3779], [RFC5280], and [RFC6487] apply to Resource Certificates and CRLs.¶

This document explicates that, in the RPKI, the CRL listed on the certificate issuer's current manifest is the one relevant and appropriate for determining the revocation status of a resource certificate. The hash in the manifest's fileList provides a cryptographic guarantee on the Certification Authority's intent that this is the most recent CRL and removes possible replay vectors.¶

6. IANA Considerations

This document has no IANA actions.¶

Acknowledgements

The authors wish to thank Tom Harrison whose observations prompted this document, Alberto Leiva, Tim Bruijnzeels, Mohamed Boucadair, Geoff Huston, and the IESG for their valuable comments and feedback.¶

Authors' Addresses