RPKI TAL: Resource Public Key Infrastructure (RPKI) Trust Anchor Locator
A file pointing to the root certificate that verifies IP address ownership
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>.
@misc{rfc7730,
series = {Request for Comments},
number = 7730,
howpublished = {RFC 7730},
publisher = {RFC Editor},
doi = {10.17487/RFC7730},
url = {https://www.rfc-editor.org/info/rfc7730},
author = {G. Huston and S. Weiler and G. Michaelson and S. Kent},
title = {{Resource Public Key Infrastructure (RPKI) Trust Anchor Locator}},
pagetotal = 8,
year = 2016,
month = jan,
} RFC text
Contents
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
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.
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
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].
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
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.
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>.
[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>.
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
AI ELI5
On this page
§1Introduction
Resource Public Key Infrastructure (RPKI) is a system where holders of IP address ranges can create cryptographically signed statements about how their addresses can be used for routing. These statements must be verified using a trust anchor, a self-signed root certificate that acts as the foundation of trust.
Instead of distributing the trust anchor certificate directly, which would need to be updated every time the certificate's resource extensions change, this RFC defines a Trust Anchor Locator (TAL). A TAL is a simple text file that tells a relying party where to retrieve the trust anchor and how to verify it is authentic.
RPKI is like a notary system for internet addresses. Instead of sending the notary's certificate each time, you just send a note about where to find it.
§2The Trust Anchor Locator Format
A TAL is a plain text file with two parts: a URI section and a public key section. The URI section contains one or more rsync:// URIs that reference exactly one object—the self-signed root certificate. These URIs are separated by line breaks. The public key section is the certificate's public key in Base64 encoding (following RFC 4648), with optional line breaks to keep lines short.
The key is kept in the TAL because it is stable: it does not change when the certificate is reissued due to resource changes, renewal, or migration to a new certificate. The URI may reference different versions of the certificate over time, but all versions must contain this same public key. This design allows the TAL to remain constant while the certificate itself evolves.
The TAL is like a note with an address and a fingerprint. The fingerprint never changes, but the person at the address can be updated.
§3Trust Anchor Considerations
The trust anchor is a self-signed X.509 CA certificate conforming to the RPKI certificate profile. Its INR extension (listing Internet Number Resources such as IP addresses and AS numbers) defines which resources the trust anchor entity is authoritative for. The trust anchor's key must be stable and not change except for planned key rollover.
For operational security, the entity issuing the trust anchor should keep its private key offline and delegate signing operations to a subordinate CA certificate. The trust anchor must be published at a stable URI: when the certificate is reissued, the replacement must be accessible at the same location. If multiple URIs are listed in the TAL, the same certificate must be found at each location, ideally on diverse, geographically distributed repository servers.
The trust anchor is like the notary's license. Its signature and identity never change, but you might check multiple copies of it at different places to make sure one is available.
§4How Relying Parties Use the TAL
A relying party (RP) uses the TAL to bootstrap trust in RPKI. First, it retrieves the certificate from one of the URIs. It then verifies that the retrieved certificate is a valid, self-signed RPKI CA certificate that conforms to RFC 6487. Most importantly, it confirms that the public key in the TAL exactly matches the public key in the certificate.
If the TAL lists multiple URIs, the RP may choose which to fetch from based on local preferences: the order given, randomly, or based on performance metrics like connection speed. If the preferred URI fails or returns a certificate with a mismatched public key, the RP tries the next URI. This provides resilience: if one repository goes down, the RP can fetch from another.
You get the note, go to one of the addresses on it, check that the person there matches the fingerprint, and if that address is down, try another one.
§5Security Considerations
Compromise of a trust anchor's private key would allow unauthorized parties to masquerade as the trust anchor and make false claims about IP address ownership. This has severe consequences for routing security. Relying parties must have high confidence in the trust anchor entities they configure, or they should establish their own trust anchors with constraints on subordinate certificates.
The TAL does not list what resources the trust anchor covers; the RP must read the certificate's INR extension. This provides operational flexibility but means relying parties must trust that the certificate issuer does not claim resources they do not control. Choosing appropriate trust anchors is critical to the security of RPKI deployments.
If the notary's signature is faked, all their documents are lies. Choose your trust anchors carefully.