Handling of Resource Public Key Infrastructure (RPKI) Certificate Revocation List (CRL) Number Extensions
updates
- rfc-6487 — A Profile for X.509 PKIX Resource Certificates
Extracted elements (11)
Although the CRL Number extension is mandatory in RPKI CRLs for compliance with the X.509 v2 CRL Profile (RFC 5280 Section 5), any reliance on it by RPKI RPs merely adds complexity because the manifest already provides unambiguous, tamper-evident CRL identification. The document therefore mandates that RPs ignore the CRL Number for ordering purposes.
In the RPKI, the ordering functionality provided by CRL Numbers is fully subsumed by monotonically increasing manifest numbers (RFC 9286 Section 4.2.1). Because an RPKI RP can always unambiguously identify exactly one current CRL via the manifest fileList and hash, the CRL Number extension adds only complexity and fragility to path validation rather than providing useful ordering information.
This document integrates Errata 3205 (Err3205) against RFC 6487 as part of its revisions to Section 7.2 (resource certification path validation).
This document updates RFC 6487, revising CRL Number handling, adjusting step 5 of the Resource Certification Path Validation procedure, and integrating Errata 3205 (Err3205). Implementations conforming to RFC 6487 must be updated to ignore the CRL Number extension as specified here.
An RPKI CA MUST include exactly two extensions in every CRL it issues: an Authority Key Identifier (AKI) and a CRL Number. No other CRL extensions are allowed.
For resource certificate path validation step 5, a revoked certificate is identified by its serial number appearing on the issuer's current CRL as identified by BOTH the issuer's current manifest AND the CRLDP of the certificate; the CRL must be valid and signed by the same key that verified the certificate.
It is RECOMMENDED that the CRL Number match the manifestNumber of the manifest that will include that CRL, per RFC 9286 Section 4.2.1.
RPKI Relying Parties 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.
RPKI Relying Parties MUST process the Authority Key Identifier (AKI) extension in every CRL issued by an RPKI CA.
In the RPKI, exactly one CRL is appropriate and relevant for determining the revocation status of a given resource certificate: 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 with a matching hash.
The hash in the manifest's fileList provides a cryptographic guarantee of the CA's intent that the listed CRL is the most recent, and removes possible replay attack vectors that could otherwise be exploited via stale CRLs bearing higher CRL Numbers.