]> Relying Party Handling of Resource Public Key Infrastructure (RPKI) Certificate Revocation List (CRL) Number Extensions
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Operations and Management Area (OPS) SIDROPS RPKI Routing Security BGP X.509 CRL This document clarifies how Resource Public Key Infrastructure (RPKI) Relying Parties (RPs) handle Certificate Revocation List (CRL) Number extensions. This document updates RFC 6487.
Introduction 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 and ). 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 ). 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 (), 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 (), 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 with clarifications for RP implementers. Refer to for more details.
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 when, and only when, they appear in all capitals, as shown here.
Related Work It is assumed that the reader is familiar with the terms and concepts described in "" and "" .
Changes from RFC 6487 This section summarizes the significant changes between and this document.
  • Clarifications for handling of CRL Numbers for RPs.
  • Integration of RFC 6487 Errata 3205.
Updates to RFC 6487 This section updates as follows:
  • First change: OLD
    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.
    NEW
    Per , CAs issue new CRLs using a monotonically increasing sequence number in the "CRL Number" extension. It is RECOMMENDED that the "CRL Number" matches the "manifestNumber" of the manifest that will include this CRL (see ).
  • Second change: 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.
    • RPs MUST ignore the CRL Number extension except for checking that it is marked as non-critical and contains a non-negative integer less than or equal to 2^159-1.
Operational Considerations This document has no additional operational considerations compared to .
Security Considerations The Security Considerations of , , and apply to Resource Certificates and CRLs. This document clarifies that, in the RPKI, there is exactly one CRL appropriate and relevant for determining the revocation status of a given resource certificate. It is the unique CRL object that is simultaneously:
  • the target of the certificate's CRL Distribution Points extension, and
  • listed in the issuing CA's current Manifest FileList and has matching hash (see ).
This is a more stringent requirement than is generally used in other X.509 PKIs. It is therefore important for RPs to use an implementation of the X.509 path validation algorithm that allows specifying the CRL objects to use for each of the intermediate CAs and the leaf.
IANA Considerations This document has no IANA actions.
References Normative References Informative References rpki-client FORT validator Routinator
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".
  • OpenBSD
Acknowledgements The authors wish to thank whose observations prompted this document, , , and for valuable feedback.