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Internet Engineering Task Force (IETF)                         G. HustonRequest for Comments: 8630                                         APNICObsoletes:7730                                                S. WeilerCategory: Standards Track                                        W3C/MITISSN: 2070-1721                                            G. Michaelson                                                                   APNIC                                                                 S. Kent                                                            Unaffiliated                                                          T. Bruijnzeels                                                              NLnet Labs                                                             August 2019Resource Public Key Infrastructure (RPKI) Trust Anchor LocatorAbstract   This document defines a Trust Anchor Locator (TAL) for the Resource   Public Key Infrastructure (RPKI).  The TAL allows Relying Parties in   the RPKI to download the current Trust Anchor (TA) Certification   Authority (CA) certificate from one or more locations and verify that   the key of this self-signed certificate matches the key on the TAL.   Thus, Relying Parties can be configured with TA keys but can allow   these TAs to change the content of their CA certificate.  In   particular, it allows TAs to change the set of IP Address Delegations   and/or Autonomous System Identifier Delegations included in the   extension(s) (RFC 3779) of their certificate.   This document obsoletes the previous definition of the TAL as   provided inRFC 7730 by adding support for Uniform Resource   Identifiers (URIs) (RFC 3986) that use HTTP over TLS (HTTPS) (RFC7230) as the scheme.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8630.Huston, et al.               Standards Track                    [Page 1]

RFC 8630                        HTTPS TAL                    August 2019Copyright Notice   Copyright (c) 2019 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents1. Introduction ....................................................21.1. Terminology ................................................31.2. Changes fromRFC 7730 ......................................32. Trust Anchor Locator ............................................32.1. Trust Anchor Locator Motivation ............................32.2. Trust Anchor Locator File Format ...........................42.3. TAL and TA Certificate Considerations ......................42.4. Example ....................................................63. Relying Party Use ...............................................64. URI Scheme Considerations .......................................75. Security Considerations .........................................86. IANA Considerations .............................................87. References ......................................................87.1. Normative References .......................................87.2. Informative References ....................................10   Acknowledgements ..................................................10   Authors' Addresses ................................................111.  Introduction   This document defines a Trust Anchor Locator (TAL) for the Resource   Public Key Infrastructure (RPKI) [RFC6480].  This format may be used   to distribute Trust Anchor (TA) material using a mix of out-of-band   and online means.  Procedures used by Relying Parties (RPs) to verify   RPKI signed objects SHOULD support this format to facilitate   interoperability between creators of TA material and RPs.  This   document obsoletes [RFC7730] by adding support for Uniform Resource   Identifiers (URIs) [RFC3986] that use HTTP over TLS (HTTPS) [RFC7230]   as the scheme.Huston, et al.               Standards Track                    [Page 2]

RFC 8630                        HTTPS TAL                    August 20191.1.  Terminology   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 inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.1.2.  Changes fromRFC 7730   The TAL format defined in this document differs from the definition   in [RFC7730] in that:   o  it allows for the use of the HTTPS scheme in URIs [RFC7230], and   o  it allows for the inclusion of an optional comment section.   Note that current RPs may not support this new format yet.   Therefore, it is RECOMMENDED that a TA operator maintain a TAL file   as defined in [RFC7730] for a time as well, until they are satisfied   that RP tooling has been updated.2.  Trust Anchor Locator2.1.  Trust Anchor Locator Motivation   This document does not propose a new format for TA material.  A TA in   the RPKI is represented by a self-signed X.509 Certification   Authority (CA) certificate, a format commonly used in PKIs and widely   supported by RP software.  This document specifies a format for data   used to retrieve and verify the authenticity of a TA in a very simple   fashion.  That data is referred to as the TAL.   The motivation for defining the TAL is to enable selected data in the   TA to change, without needing to redistribute the TA per se.   In the RPKI, certificates contain one or more extensions [RFC3779]   that can contain a set of IP Address Delegations and/or Autonomous   System Identifier Delegations.  In this document, we refer to these   delegations as the Internet Number Resources (INRs) contained in an   RPKI certificate.   The set of INRs associated with an entity acting as a TA is likely to   change over time.  Thus, if one were to use the common PKI convention   of distributing a TA to RPs in a secure fashion, then this procedure   would need to be repeated whenever the INR set for the entity acting   as a TA changed.  By distributing the TAL (in a secure fashion)Huston, et al.               Standards Track                    [Page 3]

RFC 8630                        HTTPS TAL                    August 2019   instead of distributing the TA, this problem is avoided, i.e., the   TAL is constant so long as the TA's public key and its location do   not change.   The TAL is analogous to the TrustAnchorInfo data structure specified   in [RFC5914], which is on the Standards Track.  That specification   could be used to represent the TAL, if one defined an rsync or HTTPS   URI extension for that data structure.  However, the TAL format was   adopted by RPKI implementors prior to the PKIX TA work, and the RPKI   implementor community has elected to utilize the TAL format rather   than define the requisite extension.  The community also prefers the   simplicity of the ASCII encoding of the TAL, versus the binary   (ASN.1) encoding for TrustAnchorInfo.2.2.  Trust Anchor Locator File Format   In this document, we define a TA URI as a URI that can be used to   retrieve a current TA certificate.  This URI MUST be either an rsync   URI [RFC5781] or an HTTPS URI [RFC7230].   The TAL is an ordered sequence of:   1.  an optional comment section consisting of one or more lines each       starting with the "#" character, followed by human-readable       informational UTF-8 text, conforming to the restrictions defined       inSection 2 of [RFC5198], and ending with a line break,   2.  a URI section that is comprised of one or more ordered lines,       each containing a TA URI, and ending with a line break,   3.  a line break, and   4.  a subjectPublicKeyInfo [RFC5280] in DER format [X.509], encoded       in base64 (seeSection 4 of [RFC4648]).  To avoid long lines,       line breaks MAY be inserted into the base64-encoded string.   Note that line breaks in this file can use either "<CRLF>" or "<LF>".2.3.  TAL and TA Certificate Considerations   Each TA URI in the TAL MUST reference a single object.  It MUST NOT   reference a directory or any other form of collection of objects.   The referenced object MUST be a self-signed CA certificate that   conforms to the RPKI certificate profile [RFC6487].  This certificate   is the TA in certification path discovery [RFC4158] and validation   [RFC5280] [RFC3779].Huston, et al.               Standards Track                    [Page 4]

RFC 8630                        HTTPS TAL                    August 2019   The validity interval of this TA is chosen such that (1) the   "notBefore" time predates the moment that this certificate is   published and (2) the "notAfter" time is after the planned time of   reissuance of this certificate.   The INR extension(s) of this TA MUST contain a non-empty set of   number resources.  It MUST NOT use the "inherit" form of the INR   extension(s).  The INR set described in this certificate is the set   of number resources for which the issuing entity is offering itself   as a putative TA in the RPKI [RFC6480].   The public key used to verify the TA MUST be the same as the   subjectPublicKeyInfo in the CA certificate and in the TAL.   The TA MUST contain a stable key that does not change when the   certificate is reissued due to changes in the INR extension(s), when   the certificate is renewed prior to expiration.   Because the public key in the TAL and the TA MUST be stable, this   motivates operation of that CA in an offline mode.  In that case, a   subordinate CA certificate containing the same INRs, or, in theory,   any subset of INRs, can be issued for online operations.  This allows   the entity that issues the TA to keep the corresponding private key   of this certificate offline, while issuing all relevant child   certificates under the immediate subordinate CA.  This measure also   allows the Certificate Revocation List (CRL) issued by that entity to   be used to revoke the subordinate CA certificate in the event of   suspected key compromise of this online operational key pair that is   potentially more vulnerable.   The TA MUST be published at a stable URI.  When the TA is reissued   for any reason, the replacement CA certificate MUST be accessible   using the same URI.   Because the TA is a self-signed certificate, there is no   corresponding CRL that can be used to revoke it, nor is there a   manifest [RFC6486] that lists this certificate.   If an entity wishes to withdraw a self-signed CA certificate as a   putative TA, for any reason, including key rollover, the entity MUST   remove the object from the location referenced in the TAL.   Where the TAL contains two or more TA URIs, the same self-signed   CA certificate MUST be found at each referenced location.  In order   to increase operational resilience, it is RECOMMENDED that   (1) the domain name parts of each of these URIs resolve to distinctHuston, et al.               Standards Track                    [Page 5]

RFC 8630                        HTTPS TAL                    August 2019   IP addresses that are used by a diverse set of repository publication   points and (2) these IP addresses be included in distinct Route   Origin Authorization (ROA) objects signed by different CAs.2.4.  Example         # This TAL is intended for documentation purposes only.         # Do not attempt to use this in a production setting.         rsync://rpki.example.org/rpki/hedgehog/root.cer         https://rpki.example.org/rpki/hedgehog/root.cer         MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAovWQL2lh6knDx         GUG5hbtCXvvh4AOzjhDkSHlj22gn/1oiM9IeDATIwP44vhQ6L/xvuk7W6         Kfa5ygmqQ+xOZOwTWPcrUbqaQyPNxokuivzyvqVZVDecOEqs78q58mSp9         nbtxmLRW7B67SJCBSzfa5XpVyXYEgYAjkk3fpmefU+AcxtxvvHB5OVPIa         BfPcs80ICMgHQX+fphvute9XLxjfJKJWkhZqZ0v7pZm2uhkcPx1PMGcrG         ee0WSDC3fr3erLueagpiLsFjwwpX6F+Ms8vqz45H+DKmYKvPSstZjCCq9         aJ0qANT9OtnfSDOS+aLRPjZryCNyvvBHxZXqj5YCGKtwIDAQAB3.  Relying Party Use   In order to use the TAL to retrieve and validate a (putative) TA, an   RP SHOULD:   1.  Retrieve the object referenced by (one of) the TA URI(s)       contained in the TAL.   2.  Confirm that the retrieved object is a current, self-signed RPKI       CA certificate that conforms to the profile as specified in       [RFC6487].   3.  Confirm that the public key in the TAL matches the public key in       the retrieved object.   4.  Perform other checks, as deemed appropriate (locally), to ensure       that the RP is willing to accept the entity publishing this       self-signed CA certificate to be a TA.  These tests apply to the       validity of attestations made in the context of the RPKI relating       to all resources described in the INR extension(s) of this       certificate.   An RP SHOULD perform these functions for each instance of a TAL that   it is holding for this purpose every time the RP performs a   resynchronization across the local repository cache.  In any case, an   RP also SHOULD perform these functions prior to the expiration of the   locally cached copy of the retrieved TA referenced by the TAL.Huston, et al.               Standards Track                    [Page 6]

RFC 8630                        HTTPS TAL                    August 2019   In the case where a TAL contains multiple TA URIs, an RP MAY use a   locally defined preference rule to select the URI to retrieve the   self-signed RPKI CA certificate that is to be used as a TA.  Some   examples are:   o  Using the order provided in the TAL   o  Selecting the TA URI randomly from the available list   o  Creating a prioritized list of URIs based on RP-specific      parameters, such as connection establishment delay   If the connection to the preferred URI fails or the retrieved CA   certificate public key does not match the TAL public key, the RP   SHOULD retrieve the CA certificate from the next URI, according to   the local preference ranking of URIs.4.  URI Scheme Considerations   Please note that the RSYNC protocol provides neither transport   security nor any means by which the RP can validate that they are   connected to the proper host.  Therefore, it is RECOMMENDED that   HTTPS be used as the preferred scheme.   Note that, although a Man in the Middle (MITM) cannot produce a CA   certificate that would be considered valid according to the process   described inSection 3, this type of attack can prevent the RP from   learning about an updated CA certificate.   RPs MUST do TLS certificate and host name validation when they fetch   a CA certificate using an HTTPS URI on a TAL.  RPs SHOULD log any TLS   certificate or host name validation issues found so that an operator   can investigate the cause.   It is RECOMMENDED that RPs and Repository Servers follow the Best   Current Practices outlined in [RFC7525] on the use of HTTPS   [RFC7230].  RPs SHOULD do TLS certificate and host name validation   using subjectAltName dNSName identities as described in [RFC6125].   The rules and guidelines defined in [RFC6125] apply here, with the   following considerations:   o  RPs and Repository Servers SHOULD support the DNS-ID identifier      type.  The DNS-ID identifier type SHOULD be present in Repository      Server certificates.   o  DNS names in Repository Server certificates SHOULD NOT contain the      wildcard character "*".Huston, et al.               Standards Track                    [Page 7]

RFC 8630                        HTTPS TAL                    August 2019   o  This protocol does not require the use of SRV-IDs.   o  This protocol does not require the use of URI-IDs.5.  Security Considerations   Compromise of a TA private key permits unauthorized parties to   masquerade as a TA, with potentially severe consequences.  Reliance   on an inappropriate or incorrect TA has similar potentially severe   consequences.   This TAL does not directly provide a list of resources covered by the   referenced self-signed CA certificate.  Instead, the RP is referred   to the TA itself and the INR extension(s) within this certificate.   This provides necessary operational flexibility, but it also allows   the certificate issuer to claim to be authoritative for any resource.   RPs should either (1) have great confidence in the issuers of such   certificates that they are configuring as TAs or (2) issue their own   self-signed certificate as a TA and, in doing so, impose constraints   on the subordinate certificates.6.  IANA Considerations   This document has no IANA actions.7.  References7.1.  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>.   [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>.   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform              Resource Identifier (URI): Generic Syntax", STD 66,RFC 3986, DOI 10.17487/RFC3986, January 2005,              <https://www.rfc-editor.org/info/rfc3986>.   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data              Encodings",RFC 4648, DOI 10.17487/RFC4648, October 2006,              <https://www.rfc-editor.org/info/rfc4648>.Huston, et al.               Standards Track                    [Page 8]

RFC 8630                        HTTPS TAL                    August 2019   [RFC5198]  Klensin, J. and M. Padlipsky, "Unicode Format for Network              Interchange",RFC 5198, DOI 10.17487/RFC5198, March 2008,              <https://www.rfc-editor.org/info/rfc5198>.   [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>.   [RFC5781]  Weiler, S., Ward, D., and R. Housley, "The rsync URI              Scheme",RFC 5781, DOI 10.17487/RFC5781, February 2010,              <https://www.rfc-editor.org/info/rfc5781>.   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and              Verification of Domain-Based Application Service Identity              within Internet Public Key Infrastructure Using X.509              (PKIX) Certificates in the Context of Transport Layer              Security (TLS)",RFC 6125, DOI 10.17487/RFC6125,              March 2011, <https://www.rfc-editor.org/info/rfc6125>.   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support              Secure Internet Routing",RFC 6480, DOI 10.17487/RFC6480,              February 2012, <https://www.rfc-editor.org/info/rfc6480>.   [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>.   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer              Protocol (HTTP/1.1): Message Syntax and Routing",RFC 7230, DOI 10.17487/RFC7230, June 2014,              <https://www.rfc-editor.org/info/rfc7230>.   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,              "Recommendations for Secure Use of Transport Layer              Security (TLS) and Datagram Transport Layer Security              (DTLS)",BCP 195,RFC 7525, DOI 10.17487/RFC7525,              May 2015, <https://www.rfc-editor.org/info/rfc7525>.   [RFC7730]  Huston, G., Weiler, S., Michaelson, G., and S. Kent,              "Resource Public Key Infrastructure (RPKI) Trust Anchor              Locator",RFC 7730, DOI 10.17487/RFC7730, January 2016,              <https://www.rfc-editor.org/info/rfc7730>.Huston, et al.               Standards Track                    [Page 9]

RFC 8630                        HTTPS TAL                    August 2019   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC 2119 Key Words",BCP 14,RFC 8174,              DOI 10.17487/RFC8174, May 2017,              <https://www.rfc-editor.org/info/rfc8174>.   [X.509]    ITU-T, "Information technology - Open Systems              Interconnection - The Directory: Public-key and attribute              certificate frameworks", ITU-T Recommendation X.509,              October 2016, <https://www.itu.int/rec/T-REC-X.509>.7.2.  Informative References   [RFC4158]  Cooper, M., Dzambasow, Y., Hesse, P., Joseph, S., and R.              Nicholas, "Internet X.509 Public Key Infrastructure:              Certification Path Building",RFC 4158,              DOI 10.17487/RFC4158, September 2005,              <https://www.rfc-editor.org/info/rfc4158>.   [RFC5914]  Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor              Format",RFC 5914, DOI 10.17487/RFC5914, June 2010,              <https://www.rfc-editor.org/info/rfc5914>.   [RFC6486]  Austein, R., Huston, G., Kent, S., and M. Lepinski,              "Manifests for the Resource Public Key Infrastructure              (RPKI)",RFC 6486, DOI 10.17487/RFC6486, February 2012,              <https://www.rfc-editor.org/info/rfc6486>.Acknowledgements   This approach to TA material was originally described by Robert   Kisteleki.   The authors acknowledge the contributions of Rob Austein and Randy   Bush, who assisted with drafting this document and with helpful   review comments.   The authors acknowledge the work of Roque Gagliano, Terry Manderson,   and Carlos Martinez-Cagnazzo in developing the ideas behind the   inclusion of multiple URIs in the TAL.   The authors acknowledge Job Snijders for suggesting the inclusion of   comments at the start of the TAL.Huston, et al.               Standards Track                   [Page 10]

RFC 8630                        HTTPS TAL                    August 2019Authors' Addresses   Geoff Huston   APNIC   Email: gih@apnic.net   URI:https://www.apnic.net   Samuel Weiler   W3C/MIT   Email: weiler@csail.mit.edu   George Michaelson   APNIC   Email: ggm@apnic.net   URI:https://www.apnic.net   Stephen Kent   Unaffiliated   Email: kent@alum.mit.edu   Tim Bruijnzeels   NLnet Labs   Email: tim@nlnetlabs.nl   URI:https://www.nlnetlabs.nlHuston, et al.               Standards Track                   [Page 11]