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Resource Public Key Infrastructure (RPKI) Trust Anchor Locator

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8630.
Authors Geoff Huston , Samuel Weiler , George G. Michaelson , Stephen Kent , Tim Bruijnzeels
Last updated 2019-04-11 (Latest revision 2019-03-04)
Replaces draft-tbruijnzeels-sidrops-https-tal
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Chris Morrow
Shepherd write-up Show Last changed 2019-02-27
IESG IESG state Became RFC 8630 (Proposed Standard)
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Warren "Ace" Kumari
Send notices to Chris Morrow <>
IANA IANA review state IANA OK - No Actions Needed
Network Working Group                                          G. Huston
Internet-Draft                                                     APNIC
Obsoletes: 7730 (if approved)                                  S. Weiler
Intended status: Standards Track                                 W3C/MIT
Expires: September 5, 2019                                 G. Michaelson
                                                                 S. Kent
                                                          T. Bruijnzeels
                                                              NLnet Labs
                                                           March 4, 2019

     Resource Public Key Infrastructure (RPKI) Trust Anchor Locator


   This document defines a Trust Anchor Locator (TAL) for the Resource
   Public Key Infrastructure (RPKI).  TALs allow Relying Parties in the
   RPKI to download the current Trust Anchor (TA) 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 allow these TAs to change the content of
   their CA certificate.  In particular it allows TAs to change the set
   of Internet Number Resources included in the RFC3779 extension of
   their certificate.

   This document obsoletes the previous definition of Trust Anchor
   Locators in RFC 7730 by adding support for HTTPS URIs.

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

   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 September 5, 2019.

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Copyright Notice

   Copyright (c) 2019 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
   ( 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 Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Trust Anchor Locator  . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Trust Anchor Locator Motivation . . . . . . . . . . . . .   3
     2.2.  Trust Anchor Locator File Format  . . . . . . . . . . . .   3
     2.3.  TAL and Trust Anchor Certificate Considerations . . . . .   4
     2.4.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Relying Party Use . . . . . . . . . . . . . . . . . . . . . .   6
   4.  HTTPS Considerations  . . . . . . . . . . . . . . . . . . . .   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

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 [RFC7730] by adding support for HTTPS URIs in
   a TAL.

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1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

2.  Trust Anchor Locator

2.1.  Trust Anchor Locator Motivation

   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 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 or HTTPS
   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.

2.2.  Trust Anchor Locator File Format

   In this document we define a Trust Anchor URI as a URI that can be
   used to retrieved a current Trust Anchor certificate.  This URI MUST
   be either an rsync URI [RFC5781], or an HTTPS URI [RFC7230].

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   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, and ending with a line break,

   2.  a URI section, that is comprised of one or more ordered lines,
       each containing a Trust Anchor URI, and ending with a line break,

   3.  a line break,

   4.  a subjectPublicKeyInfo [RFC5280] in DER format [X.509], encoded
       in Base64 (see Section 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 Trust Anchor Certificate Considerations

   Each Trust Anchor URI in the TAL MUST reference a single object.  It
   MUST NOT reference a directory or any other form of collection of

   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 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.

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   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

   Where the TAL contains two or more Trust Anchor 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
   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.

2.4.  Example

           # This TAL is intended for documentation purposes only.
           # Do not attempt to use this in a production setting.


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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 Trust Anchor
       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

   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

   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

   In the case where a TAL contains multiple Trust Anchor 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 Trust Anchor 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.

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4.  HTTPS Considerations

   Note that a Man in the Middle (MITM) cannot produce a CA certificate
   that would be considered valid according to the process described in
   Section 3.  However, a MITM attack can be performed to prevent the
   Relying Party from learning about an updated CA certificate.  Because
   of this, Relying Parties MUST do TLS certificate and host name
   validation when they fetch a CA certificate using an HTTPS URI on a

   Relying Party tools SHOULD log any TLS certificate or host name
   validation issues found, so that an operator can investigate the

   It is RECOMMENDED that Relying Parties and Repository Servers follow
   the Best Current Practices outlined in [RFC7525] on the use of HTTP
   over TLS (HTTPS) [RFC7230].  Relying Parties 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  Relying Parties 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 "*".

   o  A Common Name (CN) field may be present in a Repository Server
      certificate's subject name but SHOULD NOT be used for
      authentication within the rules described in [RFC6125].

   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 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

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   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

6.  IANA Considerations

   This document has no actions for IANA.

7.  Acknowledgements

   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 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.

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,

   [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,

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,

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   [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,

   [RFC5781]  Weiler, S., Ward, D., and R. Housley, "The rsync URI
              Scheme", RFC 5781, DOI 10.17487/RFC5781, February 2010,

   [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, <>.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <>.

   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487,
              DOI 10.17487/RFC6487, February 2012,

   [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,

   [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, <>.

   [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,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [X.509]    TU-T Recommendation X.509, "The Directory: Public-key and
              attribute certificate frameworks", October 2012.

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8.2.  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,

   [RFC5914]  Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor
              Format", RFC 5914, DOI 10.17487/RFC5914, June 2010,

   [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,

Authors' Addresses

   Geoff Huston


   Samuel Weiler


   George Michaelson


   Stephen Kent


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   Tim Bruijnzeels
   NLnet Labs


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