Resource Public Key Infrastructure (RPKI) Trust Anchor Locator
RFC 7730

Internet Engineering Task Force (IETF)                         G. Huston
Request for Comments: 7730                                         APNIC
Obsoletes: 6490                                                S. Weiler
Category: Standards Track                                        Parsons
ISSN: 2070-1721                                            G. Michaelson
                                                                   APNIC
                                                                 S. Kent
                                                                     BBN
                                                            January 2016

     Resource Public Key Infrastructure (RPKI) Trust Anchor Locator

Abstract

   This document defines a Trust Anchor Locator (TAL) for the Resource
   Public Key Infrastructure (RPKI).  This document obsoletes RFC 6490
   by adding support for multiple URIs in a TAL.

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 in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7730.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Trust Anchor Locator  . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Trust Anchor Locator Format . . . . . . . . . . . . . . .   2
     2.2.  TAL and Trust Anchor Certificate Considerations . . . . .   3
     2.3.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Relying Party Use . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  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 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 trust anchor material and RPs.
   This document obsoletes RFC 6490 by adding support for multiple URIs
   in a TAL.

1.1.  Terminology

   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].

2.  Trust Anchor Locator

2.1.  Trust Anchor Locator Format

   This document does not propose a new format for trust anchor
   material.  A trust anchor 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 trust anchor 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
   trust anchor to change, without needing to effect redistribution of
   the trust anchor per se.  In the RPKI, certificates contain

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   extensions that represent Internet Number Resources (INRs) [RFC3779].
   The set of INRs associated with an entity acting as a trust anchor is
   likely to change over time.  Thus, if one were to use the common PKI
   convention of distributing a trust anchor to RPs in a secure fashion,
   then this procedure would need to be repeated whenever the INR set
   for the entity acting as a trust anchor changed.  By distributing the
   TAL (in a secure fashion), instead of distributing the trust anchor,
   this problem is avoided, i.e., the TAL is constant so long as the
   trust anchor'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 URI
   extension for that data structure.  However, the TAL format was
   adopted by RPKI implementors prior to the PKIX trust anchor work, and
   the RPKI implementer 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.

   The TAL is an ordered sequence of:

      1)  a URI section,

      2)  a <CRLF> or <LF> line break,

      3)  a subjectPublicKeyInfo [RFC5280] in DER format [X.509],
          encoded in Base64 (see Section 4 of [RFC4648]).  To avoid long
          lines, <CRLF> or <LF> line breaks MAY be inserted into the
          Base64-encoded string.

   where the URI section is comprised of one of more of the ordered
   sequence of:

      1.1)  an rsync URI [RFC5781],

      1.2)  a <CRLF> or <LF> line break.

2.2.  TAL and Trust Anchor Certificate Considerations

   Each rsync 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 trust anchor in certification path discovery [RFC4158] and
   validation [RFC5280] [RFC3779].

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   The validity interval of this trust anchor SHOULD reflect the
   anticipated period of stability of the particular set of INRs that
   are associated with the putative trust anchor.

   The INR extension(s) of this trust anchor 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 trust anchor in the RPKI [RFC6480].

   The public key used to verify the trust anchor MUST be the same as
   the subjectPublicKeyInfo in the CA certificate and in the TAL.

   The trust anchor MUST contain a stable key.  This key MUST NOT change
   when the certificate is reissued due to changes in the INR
   extension(s), when the certificate is renewed prior to expiration, or
   for any reason other than a key change.

   Because the public key in the TAL and the trust anchor MUST be
   stable, this motivates operation of that CA in an offline mode.
   Thus, the entity that issues the trust anchor SHOULD issue a
   subordinate CA certificate that contains the same INRs (via the use
   of the "inherit" option in the INR extensions of the subordinate
   certificate).  This allows the entity that issues the trust anchor 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 trust anchor MUST be published at a stable URI.  When the trust
   anchor is reissued for any reason, the replacement CA certificate
   MUST be accessible using the same URI.

   Because the trust anchor 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 trust anchor, 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 rsync URIs, then the same self-
   signed CA certificate MUST be found at each referenced location.  In
   order to increase operational resilience, it is RECOMMENDED that the
   domain name parts of each of these URIs resolve to distinct IP

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   addresses that are used by a diverse set of repository publication
   points, and these IP addresses be included in distinct Route Origin
   Authorizations (ROAs) objects signed by different CAs.

2.3.  Example

   rsync://rpki.example.org/rpki/hedgehog/root.cer

   MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAovWQL2lh6knDx
   GUG5hbtCXvvh4AOzjhDkSHlj22gn/1oiM9IeDATIwP44vhQ6L/xvuk7W6
   Kfa5ygmqQ+xOZOwTWPcrUbqaQyPNxokuivzyvqVZVDecOEqs78q58mSp9
   nbtxmLRW7B67SJCBSzfa5XpVyXYEgYAjkk3fpmefU+AcxtxvvHB5OVPIa
   BfPcs80ICMgHQX+fphvute9XLxjfJKJWkhZqZ0v7pZm2uhkcPx1PMGcrG
   ee0WSDC3fr3erLueagpiLsFjwwpX6F+Ms8vqz45H+DKmYKvPSstZjCCq9
   aJ0qANT9OtnfSDOS+aLRPjZryCNyvvBHxZXqj5YCGKtwIDAQAB

3.  Relying Party Use

   In order to use the TAL to retrieve and validate a (putative) trust
   anchor, an RP SHOULD:

   1.  Retrieve the object referenced by (one of) the 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 trust anchor.  These tests apply to
       the validity of attestations made in the context of the RPKI
       relating to all resources described in the INR extension of this
       certificate.

   An RP SHOULD perform these functions for each instance of 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 trust anchor referenced by the
   TAL.

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   In the case where a TAL contains multiple 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 trust anchor.
   Some examples are:

   o  Using the order provided in the TAL
   o  Selecting the 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.  Security Considerations

   Compromise of a trust anchor private key permits unauthorized parties
   to masquerade as a trust anchor, with potentially severe
   consequences.  Reliance on an inappropriate or incorrect trust anchor
   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 trust anchor 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.  Relying parties should either have great confidence in
   the issuers of such certificates that they are configuring as trust
   anchors, or they should issue their own self-signed certificate as a
   trust anchor and, in doing so, impose constraints on the subordinate
   certificates.

5.  References

5.1.  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,
              <http://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,
              <http://www.rfc-editor.org/info/rfc3779>.

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   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <http://www.rfc-editor.org/info/rfc4648>.

   [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,
              <http://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,
              <http://www.rfc-editor.org/info/rfc5781>.

   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487,
              DOI 10.17487/RFC6487, February 2012,
              <http://www.rfc-editor.org/info/rfc6487>.

   [X.509]    ITU-T, "The Directory: Public-key and attribute
              certificate frameworks", ITU-T Recommendation X.509,
              ISO/IEC 9594-8, October 2012.

5.2.  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,
              <http://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,
              <http://www.rfc-editor.org/info/rfc5914>.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <http://www.rfc-editor.org/info/rfc6480>.

   [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,
              <http://www.rfc-editor.org/info/rfc6486>.

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Acknowledgments

   This approach to trust anchor 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 with work of Roque Gagliano, Terry Manderson,
   and Carlos Martinez Cagnazzo in developing the ideas behind the
   inclusion of multiple URIs in the TAL.

Authors' Addresses

   Geoff Huston
   APNIC

   Email: gih@apnic.net
   URI:   http://www.apnic.net

   Samuel Weiler
   Parsons
   7110 Samuel Morse Drive
   Columbia, MD  21046
   United States

   Email: weiler@tislabs.com

   George Michaelson
   APNIC

   Email: ggm@apnic.net
   URI:   http://www.apnic.net

   Stephen Kent
   BBN Technologies
   10 Moulton St.
   Cambridge, MA  02138
   United States

   Email: kent@bbn.com

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