Internet Engineering Task Force T. Harrison Internet-Draft G. Michaelson Updates: RFC9286 (if approved) APNIC Intended status: Standards Track J. Snijders Expires: 24 November 2025 23 May 2025 RPKI Manifest Number Handling draft-ietf-sidrops-manifest-numbers-04 Abstract The Resource Public Key Infrastructure (RPKI) makes use of signed objects called manifests. A manifest lists each file that a publisher intends to include within an RPKI repository, and can be used to detect certain forms of attack against a repository. Manifests include a "manifest number" (manifestNumber), which the publisher must increment whenever it issues a new manifest, and Relying Parties (RPs) are required to verify that a newly-retrieved manifest for a given Certification Authority (CA) has a higher manifestNumber than the previously-validated manifest. However, the manifestNumber field is 20 octets in length (i.e. not unbounded), and no behaviour is specified for when a manifestNumber reaches the largest possible value. This document specifies publisher and RP behaviour for this scenario. 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 24 November 2025. Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. Harrison, et al. Expires 24 November 2025 [Page 1] Internet-Draft RPKI Manifest Number Handling May 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 . . . . . . . . . . . . . . . . . . 4 2. Manifest Number Handling . . . . . . . . . . . . . . . . . . 4 3. General Repository Handling . . . . . . . . . . . . . . . . . 5 4. Operational Considerations . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. Implementation status . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . 6 8.2. Informative References . . . . . . . . . . . . . . . . . 7 Appendix A. Serial Number Arithmetic . . . . . . . . . . . . . . 8 Appendix B. Manifest thisUpdate . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction The Resource Public Key Infrastructure (RPKI) [RFC6480] makes use of signed objects [RFC6488] called manifests [RFC9286]. A manifest lists each file that a publisher intends to include within an RPKI repository [RFC6481], and can be used to detect certain forms of attack against a repository. Manifests include a "manifest number" (manifestNumber), which the publisher must increment whenever it issues a new manifest, and Relying Parties (RPs) are required to verify that a newly-retrieved manifest for a given Certification Authority (CA) has a higher manifestNumber than the previously- validated manifest (see Section 4.2.1 of [RFC9286]). Harrison, et al. Expires 24 November 2025 [Page 2] Internet-Draft RPKI Manifest Number Handling May 2025 However, the manifestNumber field is 20 octets in length (i.e. not unbounded), and no behaviour is specified for when a manifestNumber reaches the largest possible value (2^159-1). When that value is reached, some RP implementations will accept a new manifest for the CA only once the current manifest has expired, while others will not accept a new manifest at all. (For the purposes of [RFC9286], a "CA" is represented by a CA certificate with a stable location and a stable private key. Reissuing a CA certificate with changed resources or a changed expiry date does not change the identity of the CA such that the stored manifestNumber for the CA is reset, for example.) While it is practically impossible for a publisher to reach the largest possible value under normal operating conditions (it would require that the publisher issue one manifest per second for 23,171,956,451,847,141,650,870 quintillion years), there is a chance that it could be reached due to bugs in the issuance or publication systems or incorrect/inadvertent use of those systems. For example: Incrementing by large values when issuing manifests, such that the time to reach that largest value is reduced. Reissuing new manifests in an infinite delay-free loop, such that the manifestNumber increases by a large value in a comparatively short period of time. Inadvertently setting the manifestNumber to the largest possible value, such that the publisher will no longer be able to publish usable manifests for that repository. These scenarios might also arise in combination and be more severe as a result: for example, a large manifest number increment bug in conjunction with a manifest reissuance loop problem. For a subordinate CA, the risk of repository invalidation due to this problem can be addressed by the publisher simply using the key rollover process ([RFC6489]) to get a new CA certificate. RPs will treat this new certificate as though it represents a distinct CA, and the manifestNumber can be reset at that point. However, this option is not available for RPKI Trust Anchors (TAs). If a TA publishes a manifest with the largest-possible manifestNumber value, then it is difficult to rely on the TA after that point, since (per earlier comments) some RPs will not accept a new manifest until the current one has expired, while others will reject all new manifests indefinitely. Particularly in the case of TAs, the manifest validity period may be quite long, too. Issuing a new TA and distributing the associated TAL to clients would involve a large Harrison, et al. Expires 24 November 2025 [Page 3] Internet-Draft RPKI Manifest Number Handling May 2025 amount of work for TA operators and RPs. Additionally, depending on the RP implementation being used, there would be a limited degree of RPKI protection by way of that TA for the time between the issuance of the problematic manifest and the installation of the new TAL. In order to avoid these problems, this document defines how publishers and RPs can handle this scenario in order to facilitate ongoing use of an affected repository. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] [RFC8174]. 2. Manifest Number Handling For a given CA, an RP MUST NOT reject a new manifest issued by that CA on the basis of it not having a higher manifestNumber than a previously-validated manifest if the new manifest has a different filename from that of the previously-validated manifest. In other words, an RP MUST reset its stored manifestNumber for a given CA if the CA changes the filename of its manifest. With this behaviour, it is possible for a CA to be configured such that any time it issues a new manifest, it uses a new filename for that manifest. If a CA were configured in this way, the manifestNumber validation set out in Section 4.2.1 of [RFC9286] would have no purpose. To avoid this outcome, CAs SHOULD NOT use new filenames for manifests except in situations where it is necessary to ensure the ongoing validity of the CA or its repository. Similarly, RP software SHOULD alert its operators when a manifest filename changes for a given CA. To avoid certain forms of replay attack, the RP MUST verify that the URI in the accessLocation in one of the id-ad-signedObject accessMethods in the manifest's Subject Information Access (SIA) extension exactly matches the URI presented in the RPKI Repository Delta Protocol (RRDP) [RFC8182] "publish" element or the path presented by remote rsync servers. Section 2.2 of [RFC6481] contains non-normative guidance for the naming of manifest files in repositories. While a CA that supports the behaviour described in this section cannot preserve the exact filename suggested by that text (per Section 2.1 of [RFC4387]), the CA SHOULD still ensure that the filename is a value derived from the public key of the CA, per the more general guidance in that section. Harrison, et al. Expires 24 November 2025 [Page 4] Internet-Draft RPKI Manifest Number Handling May 2025 A CA specifies its manifest URI by way of an SIA entry with an accessMethod of id-ad-rpkiManifest ([RFC6487]). For the purposes of this document, the manifest filename is the final segment of the path of the accessLocation URI from that SIA entry. Section 4.8.8.1 of [RFC6487] states that a CA may include in its certificate multiple id-ad-rpkiManifest SIA entries. For comparisons, the RP may use the filename from any one of the id-ad- rpkiManifest SIA entries in the previously-validated CA certificate. If that filename does not appear in any of the id-ad-rpkiManifest SIA entries in the CA certificate that is currently being validated, then the manifest filename has changed, for the purposes of this section. The corollary of this behaviour is that a CA that includes multiple id-ad-rpkiManifest SIA entries in its certificate and wants to rely on the behaviour defined in this document MUST ensure that none of the manifest filenames in the previous CA certificate appear in the newly-issued CA certificate. Note that the approach set out in this section is different from that described in Section 3.2.1 of [RFC8488]. 3. General Repository Handling The previous section contains a specific update for the handling of manifest numbers, in order to address one potential permanent invalidity scenario. RPs that encounter other permanent invalidity scenarios SHOULD also consider how those can be addressed such that the scenario does not require the relevant CA or TA to perform a key rollover operation. For example, in the event that an RP recognises that a permanent invalidity scenario has occurred, the RP could alert the operator and provide an option to the operator to stop relying on cached data for the affected repository, so that the CA can rectify the problem. 4. Operational Considerations CA software may opt to support the manifest number reset functionality in various ways. For example, it could change the manifest filename when the manifestNumber reaches a certain threshold, or it could alert the operator in this scenario and request confirmation that the filename should be changed. 5. IANA Considerations This document has no actions for IANA. Harrison, et al. Expires 24 November 2025 [Page 5] Internet-Draft RPKI Manifest Number Handling May 2025 6. Implementation status This section is to be removed before publishing as an RFC. 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 [RFC7942]. 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 [RFC7942], "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] * Routinator [routinator] 7. Acknowledgements The authors would like to thank Theo Buehler, Ben Maddison, Rob Austein, Tim Bruijnzeels, and Russ Housley for their review and feedback on this document. 8. References 8.1. 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, . [RFC4387] Gutmann, P., Ed., "Internet X.509 Public Key Infrastructure Operational Protocols: Certificate Store Access via HTTP", RFC 4387, DOI 10.17487/RFC4387, February 2006, . Harrison, et al. Expires 24 November 2025 [Page 6] Internet-Draft RPKI Manifest Number Handling May 2025 [RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for X.509 PKIX Resource Certificates", RFC 6487, DOI 10.17487/RFC6487, February 2012, . [RFC6488] Lepinski, M., Chi, A., and S. Kent, "Signed Object Template for the Resource Public Key Infrastructure (RPKI)", RFC 6488, DOI 10.17487/RFC6488, 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, . [RFC8182] Bruijnzeels, T., Muravskiy, O., Weber, B., and R. Austein, "The RPKI Repository Delta Protocol (RRDP)", RFC 8182, DOI 10.17487/RFC8182, July 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, . 8.2. Informative References [I-D.ietf-sidrops-rpki-crl-numbers] Snijders, J., Maddison, B., and T. Buehler, "Handling of Resource Public Key Infrastructure (RPKI) Certificate Revocation List (CRL) Number Extensions", Work in Progress, Internet-Draft, draft-ietf-sidrops-rpki-crl- numbers-05, 22 May 2025, . [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, DOI 10.17487/RFC1982, August 1996, . [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, . [RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480, February 2012, . Harrison, et al. Expires 24 November 2025 [Page 7] Internet-Draft RPKI Manifest Number Handling May 2025 [RFC6481] Huston, G., Loomans, R., and G. Michaelson, "A Profile for Resource Certificate Repository Structure", RFC 6481, DOI 10.17487/RFC6481, February 2012, . [RFC6489] Huston, G., Michaelson, G., and S. Kent, "Certification Authority (CA) Key Rollover in the Resource Public Key Infrastructure (RPKI)", BCP 174, RFC 6489, DOI 10.17487/RFC6489, February 2012, . [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, July 2016, . [RFC8488] Muravskiy, O. and T. Bruijnzeels, "RIPE NCC's Implementation of Resource Public Key Infrastructure (RPKI) Certificate Tree Validation", RFC 8488, DOI 10.17487/RFC8488, December 2018, . [RFC8630] Huston, G., Weiler, S., Michaelson, G., Kent, S., and T. Bruijnzeels, "Resource Public Key Infrastructure (RPKI) Trust Anchor Locator", RFC 8630, DOI 10.17487/RFC8630, August 2019, . [routinator] NLnet Labs, "Routinator", June 2024, . [rpki-client] OpenBSD Project, "rpki-client", January 2024, . Appendix A. Serial Number Arithmetic Serial number arithmetic [RFC1982] is an approach that has been used in the DNS context (among others) to permit the indefinite use of a finite number space. At least in theory, it would be possible to use a similar approach with the manifestNumber field as well. Harrison, et al. Expires 24 November 2025 [Page 8] Internet-Draft RPKI Manifest Number Handling May 2025 However, unlike the corresponding DNS context with Start of Authority (SOA) resource records, an RPKI CA does not have visibility into or control over RPKI RPs generally. This means that it is not possible to select an updated manifestNumber value or to manage the relevant state transitions so as to guarantee that all RPs will have valid state at the end of the process. The approach proposed in Section 2 does not have this problem. Appendix B. Manifest thisUpdate The thisUpdate field in the manifest object is of type GeneralizedTime, defined in Section 4.1.2.5.2 of [RFC5280]. This type has a maximum value of 99991231235959Z (i.e. 31 December 9999 23:59:59 GMT). Section 4.2.1 of [RFC9286] requires that "[e]ach RP MUST verify that this field value is greater (more recent) than the most recent manifest it has validated", so it would appear to be subject to the same problem as for manifest numbers. However, during validation, if the RP detects that the current time is not between the manifest thisUpdate and nextUpdate values, the RP must treat the fetch as a failed fetch. Therefore, the RP will not cache a manifest with a current date far in the future, and the CA can rectify the problem here by reissuing the relevant manifest with the correct date. Authors' Addresses Tom Harrison Asia Pacific Network Information Centre 6 Cordelia St South Brisbane QLD 4101 Australia Email: tomh@apnic.net George G. Michaelson Asia-Pacific Network Information Centre 6 Cordelia St South Brisbane QLD 4101 Australia Email: ggm@apnic.net Job Snijders Amsterdam Netherlands Email: job@sobornost.net Harrison, et al. Expires 24 November 2025 [Page 9]