SIDROPS J. Snijders
Internet-Draft
Updates: 6487 (if approved) B. Maddison
Intended status: Standards Track Workonline
Expires: 26 September 2025 T. Buehler
OpenBSD
25 March 2025
Handling of Resource Public Key Infrastructure (RPKI) Certificate
Revocation List (CRL) Number Extensions
draft-ietf-sidrops-rpki-crl-numbers-04
Abstract
This document revises how the Resource Public Key Infrastructure
(RPKI) handles Certificate Revocation List (CRL) Number extensions.
This document updates RFC 6487.
Status of This Memo
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Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Related Work . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Changes from RFC 6487 . . . . . . . . . . . . . . . . . . 3
2. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Updates to RFC 6487 . . . . . . . . . . . . . . . . . . . . . 4
3.1. Updates to Section 5 . . . . . . . . . . . . . . . . . . 4
3.2. Update to Section 7.2 . . . . . . . . . . . . . . . . . . 5
4. Operational Considerations . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Implementation status - RFC EDITOR: REMOVE BEFORE
PUBLICATION . . . . . . . . . . . . . . . . . . . . . . . 7
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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
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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.
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], "A Profile
for Resource Certificate Repository Structure" [RFC6481], and
"Manifests for the Resource Public Key Infrastructure (RPKI)"
[RFC9286].
1.3. Changes from RFC 6487
This section summarizes the significant changes between [RFC6487] and
this document.
* Revision of CRL Number handling.
* Adjustment of step 5 of the Resource Certification Path
Validation.
* Integration of RFC 6487 Errata 3205.
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2. Summary
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 Section 4.2.1 of [RFC9286]).
In particular, a resource certificate cannot be validated without
recourse to the current Manifest of the certificate's issuer.
3. Updates to RFC 6487
3.1. Updates to Section 5
This section updates Section 5 of [RFC6487] 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 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
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| 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.
3.2. Update to Section 7.2
This section updates Section 7.2 of [RFC6487] as follows:
OLD
| 5. The issuer has not revoked the certificate. A revoked
| certificate is identified by the certificate's serial number
| being listed on the issuer's current CRL, as identified by the
| CRLDP of the certificate, the CRL is itself valid, and the
| public key used to verify the signature on the CRL is the same
| public key used to verify the certificate itself.
NEW
| 5. The issuer has not revoked the certificate. A revoked
| certificate is identified by the certificate's serial number
| being listed on the issuer's current CRL, as identified by the
| issuer's current Manifest and the CRLDP of the certificate.
| The CRL is itself valid and the public key used to verify the
| signature on the CRL is the same public key used to verify the
| certificate itself.
4. Operational Considerations
This document has no additional operational considerations compared
to Section 9 of [RFC6487].
5. Security Considerations
The Security Considerations of [RFC3779], [RFC5280], and [RFC6487]
apply to Resource Certificates and CRLs.
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This document explicates that, in the RPKI, the CRL listed on the
certificate issuer's current Manifest is the one relevant and
appropriate for determinining the revocation status of a resouce
certificate. By way of the hash in the manifest's FileList this
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.
7. References
7.1. 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,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6481] Huston, G., Loomans, R., and G. Michaelson, "A Profile for
Resource Certificate Repository Structure", RFC 6481,
DOI 10.17487/RFC6481, February 2012,
<https://www.rfc-editor.org/info/rfc6481>.
[RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for
X.509 PKIX Resource Certificates", RFC 6487,
DOI 10.17487/RFC6487, February 2012,
<https://www.rfc-editor.org/info/rfc6487>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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,
<https://www.rfc-editor.org/info/rfc9286>.
7.2. Informative References
[FORT] Leiva, A., "FORT validator",
<https://fortproject.net/en/validator>.
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[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,
<https://www.rfc-editor.org/info/rfc3779>.
[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,
<https://www.rfc-editor.org/info/rfc5280>.
[routinator]
NLnetLabs, "Routinator",
<https://github.com/NLnetLabs/routinator>.
[rpki-client]
Jeker, C., Snijders, J., Dzonsons, K., and T. Buehler,
"rpki-client", June 2024, <https://www.rpki-client.org/>.
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]
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Acknowledgements
The authors wish to thank Tom Harrison whose observations prompted
this document, Alberto Leiva, Tim Bruijnzeels, Mohamed Boucadair, and
Geoff Huston 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
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