SIDROPS J. Snijders Internet-Draft Updates: 6487 (if approved) B. Maddison Intended status: Standards Track Workonline Expires: 21 September 2025 T. Buehler OpenBSD 20 March 2025 Relying Party Handling of Resource Public Key Infrastructure (RPKI) Certificate Revocation List (CRL) Number Extensions draft-ietf-sidrops-rpki-crl-numbers-03 Abstract 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 https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 21 September 2025. Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. Snijders, et al. Expires 21 September 2025 [Page 1] Internet-Draft RPKI CRL Number handling for RPs March 2025 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.2. Related Work . . . . . . . . . . . . . . . . . . . . . . 3 1.3. Changes from RFC 6487 . . . . . . . . . . . . . . . . . . 3 2. Updates to RFC 6487 . . . . . . . . . . . . . . . . . . . . . 3 3. Operational Considerations . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 6.1. Normative References . . . . . . . . . . . . . . . . . . 5 6.2. Informative References . . . . . . . . . . . . . . . . . 5 Appendix A. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION . . . . . . . . . . . . . . . . . . . . . . . 6 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 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 Snijders, et al. Expires 21 September 2025 [Page 2] Internet-Draft RPKI CRL Number handling for RPs March 2025 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] with clarifications for RP implementers. Refer to Section 2 for more details. 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. 1.2. Related Work It is assumed that the reader is familiar with the terms and concepts described in "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile" [RFC5280] and "A Profile for Resource Certificate Repository Structure" [RFC6481]. 1.3. Changes from RFC 6487 This section summarizes the significant changes between [RFC6487] and this document. * Clarifications for handling of CRL Numbers for RPs. * Integration of RFC 6487 Errata 3205. 2. Updates to RFC 6487 This section updates Section 5 of [RFC6487] as follows: * First change: OLD Snijders, et al. Expires 21 September 2025 [Page 3] Internet-Draft RPKI CRL Number handling for RPs March 2025 | 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 Section 5.2.3 of [RFC5280], 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 Section 4.2.1 of [RFC9286]). * 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. 3. Operational Considerations This document has no additional operational considerations compared to Section 9 of [RFC6487]. 4. Security Considerations The Security Considerations of [RFC3779], [RFC5280], and [RFC6487] 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: Snijders, et al. Expires 21 September 2025 [Page 4] Internet-Draft RPKI CRL Number handling for RPs March 2025 * 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 Section 4.2.1 of [RFC9286]). 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. 5. IANA Considerations This document has no IANA actions. 6. References 6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC6481] Huston, G., Loomans, R., and G. Michaelson, "A Profile for Resource Certificate Repository Structure", RFC 6481, DOI 10.17487/RFC6481, February 2012, . [RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for X.509 PKIX Resource Certificates", RFC 6487, DOI 10.17487/RFC6487, February 2012, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9286] Austein, R., Huston, G., Kent, S., and M. Lepinski, "Manifests for the Resource Public Key Infrastructure (RPKI)", RFC 9286, DOI 10.17487/RFC9286, June 2022, . 6.2. Informative References [FORT] Leiva, A., "FORT validator", . Snijders, et al. Expires 21 September 2025 [Page 5] Internet-Draft RPKI CRL Number handling for RPs March 2025 [RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP Addresses and AS Identifiers", RFC 3779, DOI 10.17487/RFC3779, June 2004, . [RFC5280] 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, May 2008, . [routinator] NLnetLabs, "Routinator", . [rpki-client] Jeker, C., Snijders, J., Dzonsons, K., and T. Buehler, "rpki-client", June 2024, . Appendix A. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION 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 [rpki-client] * [FORT] * [routinator] Snijders, et al. Expires 21 September 2025 [Page 6] Internet-Draft RPKI CRL Number handling for RPs March 2025 Acknowledgements The authors wish to thank Tom Harrison whose observations prompted this document, Alberto Leiva, Tim Bruijnzeels, and Mohamed Boucadair for valuable feedback. Authors' Addresses Job Snijders Amsterdam The Netherlands Email: job@sobornost.net Ben Maddison Workonline Cape Town South Africa Email: benm@workonline.africa Theo Buehler OpenBSD Switzerland Email: tb@openbsd.org Snijders, et al. Expires 21 September 2025 [Page 7]