Internet Engineering Task Force (IETF)                         G. Huston
Request for Comments: 6490                                         APNIC
Category: Standards Track                                      S. Weiler
ISSN: 2070-1721                                             SPARTA, Inc.
                                                          G. Michaelson
                                                                  APNIC
                                                                S. Kent
                                                                    BBN
                                                          February 2012


    Resource Public Key Infrastructure (RPKI) Trust Anchor Locator

Abstract

  This document defines a Trust Anchor Locator (TAL) for the Resource
  Public Key Infrastructure (RPKI).

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/rfc6490.

Copyright Notice

  Copyright (c) 2012 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
  Provisions Relating to IETF Documents
  (http://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.





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RFC 6490                RPKI Trust Anchor Locator          February 2012


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 ....................................................4
  3. Relying Party Use ...............................................5
  4. Security Considerations .........................................5
  5. Acknowledgments .................................................6
  6. References ......................................................6
     6.1. Normative References .......................................6
     6.2. Informative References .....................................6

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.

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
  extensions that represent Internet Number Resources (INRs) [RFC3779].
  The set of INRs associated with an entity likely will change over
  time.  Thus, if one were to use the common PKI convention of



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RFC 6490                RPKI Trust Anchor Locator          February 2012


  distributing a trust anchor to RPs in a secure fashion, this
  procedure would need to be repeated whenever the INR set for the
  trust anchor changed.  By distributing the TAL (in a secure fashion)
  instead of 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 [RFC5914]
  adopted as a PKIX standard.  That standard 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) An rsync URI [RFC5781],
  2) A <CRLF> or <LF> line break, and
  3) A subjectPublicKeyInfo [RFC5280] in DER format [X.509], encoded in
     Base64 (see Section 4 of [RFC4648]).

2.2.  TAL and Trust Anchor Certificate Considerations

  The 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].

  The validity interval of this trust anchor SHOULD reflect the
  anticipated period of stability for 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.





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RFC 6490                RPKI Trust Anchor Locator          February 2012


  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 off-line 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 off-line,
  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
  potentially more vulnerable online operational key pair.

  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.

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










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RFC 6490                RPKI Trust Anchor Locator          February 2012


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 the URI 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 checks 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
  re-synchronization 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.

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.  For more information on this approach, see [TA-MGMT].






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RFC 6490                RPKI Trust Anchor Locator          February 2012


5.  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 earlier draft versions of this document and
  with helpful review comments.

6.  References

6.1.  Normative References

  [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

  [RFC3779]  Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
             Addresses and AS Identifiers", RFC 3779, June 2004.

  [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
             Encodings", RFC 4648, October 2006.

  [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, May 2008.

  [RFC5781]  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, May 2008.

  [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
             X.509 PKIX Resource Certificates", RFC 6487, February
             2012.

  [X.509]    ITU-T, "Recommendation X.509: The Directory -
             Authentication Framework", 2000.

6.2.  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, September 2005.

  [RFC5914]  Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor
             Format", RFC 5914, June 2010.




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RFC 6490                RPKI Trust Anchor Locator          February 2012


  [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
             Secure Internet Routing", RFC 6480, February 2012.

  [RFC6486]  Austein, R., Huston, G., Kent, S., and M. Lepinski,
             "Manifests for the Resource Public Key Infrastructure
             (RPKI)", RFC 6486, February 2012.

  [TA-MGMT]  Reynolds, M. and S. Kent, "Local Trust Anchor Management
             for the Resource Public Key Infrastructure", Work in
             Progress, December 2011.

Authors' Addresses

  Geoff Huston
  APNIC

  EMail: [email protected]
  URI:   http://www.apnic.net


  Samuel Weiler
  SPARTA, Inc.
  7110 Samuel Morse Drive
  Columbia, Maryland  21046
  USA

  EMail: [email protected]


  George Michaelson
  APNIC

  EMail: [email protected]
  URI:   http://www.apnic.net


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

  EMail: [email protected]








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