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IETF RFC 6490
Last modified on Saturday, February 4th, 2012
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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/RFC 6490.
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.
Huston, et al. Standards Track PAGE 1 
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) [RFC 6480]. 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 [RFC 2119].
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) [RFC 3779].
The set of INRs associated with an entity likely will change over
time. Thus, if one were to use the common PKI convention of
Huston, et al. Standards Track PAGE 2
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 [RFC 5914]
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 [RFC 5781],
2) A <CRLF> or <LF> line break, and
3) A subjectPublicKeyInfo [RFC 5280] in DER format [X.509], encoded in
Base64 (see Section 4 of [RFC 4648]).
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 [RFC 6487]. This certificate
is the trust anchor in certification path discovery [RFC 4158] and
validation [RFC 5280] [RFC 3779].
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 [RFC 6480].
The public key used to verify the trust anchor MUST be the same as
the subjectPublicKeyInfo in the CA certificate and in the TAL.
Huston, et al. Standards Track PAGE 3
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 [RFC 6486] 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
Huston, et al. Standards Track PAGE 4
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
[RFC 6487].
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].
Huston, et al. Standards Track PAGE 5
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
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779, June 2004.
[RFC 4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC 5280] 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.
[RFC 5781] 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.
[RFC 6487] 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
[RFC 4158] Cooper, M., Dzambasow, Y., Hesse, P., Joseph, S., and R.
Nicholas, "Internet X.509 Public Key Infrastructure:
Certification Path Building", RFC 4158, September 2005.
[RFC 5914] Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor
Format", RFC 5914, June 2010.
Huston, et al. Standards Track PAGE 6
RFC 6490 RPKI Trust Anchor Locator February 2012
[RFC 6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, February 2012.
[RFC 6486] 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: gih@apnic.net
URI: http://www.apnic.net
Samuel Weiler
SPARTA, Inc.
7110 Samuel Morse Drive
Columbia, Maryland 21046
USA
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
USA
EMail: kent@bbn.com
Huston, et al. Standards Track PAGE 7
RFC TOTAL SIZE: 15004 bytes
PUBLICATION DATE: Saturday, February 4th, 2012
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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