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

Introduction 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 and ). 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 ). 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 MUST ignore the CRL Number extension. This document updates with clarifications for RP implementers.

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 this document.

Clarifications for handling of CRL Numbers for RPs.
Incorporated RFC 6487 Errata 3205.

Updates to RFC 6487 This section updates .

In Section , 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 , this paragraph is changed. 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.