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Internet Engineering Task Force (IETF) G. Huston
Request for Comments: 8630 APNIC
Obsoletes: 7730 S. Weiler
Category: Standards Track W3C/MIT
ISSN: 2070-1721 G. Michaelson
APNIC
S. Kent
Unaffiliated
T. Bruijnzeels
NLnet Labs
August 2019
Resource Public Key Infrastructure (RPKI) Trust Anchor Locator
Abstract
This document defines a Trust Anchor Locator (TAL) for the Resource
Public Key Infrastructure (RPKI). The TAL allows Relying Parties in
the RPKI to download the current Trust Anchor (TA) Certification
Authority (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 can allow
these TAs to change the content of their CA certificate. In
particular, it allows TAs to change the set of IP Address Delegations
and/or Autonomous System Identifier Delegations included in the
extension(s) (RFC 3779) of their certificate.
This document obsoletes the previous definition of the TAL as
provided in RFC 7730 by adding support for Uniform Resource
Identifiers (URIs) (RFC 3986) that use HTTP over TLS (HTTPS) (RFC
7230) as the scheme.
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 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8630.
Huston, et al. Standards Track [Page 1]
RFC 8630 HTTPS TAL August 2019
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
(https://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 ................................................3
1.2. Changes from RFC 7730 ......................................3
2. Trust Anchor Locator ............................................3
2.1. Trust Anchor Locator Motivation ............................3
2.2. Trust Anchor Locator File Format ...........................4
2.3. TAL and TA Certificate Considerations ......................4
2.4. Example ....................................................6
3. Relying Party Use ...............................................6
4. URI Scheme Considerations .......................................7
5. Security Considerations .........................................8
6. IANA Considerations .............................................8
7. References ......................................................8
7.1. Normative References .......................................8
7.2. Informative References ....................................10
Acknowledgements ..................................................10
Authors' Addresses ................................................11
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 (TA) 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 TA material and RPs. This
document obsoletes [RFC7730] by adding support for Uniform Resource
Identifiers (URIs) [RFC3986] that use HTTP over TLS (HTTPS) [RFC7230]
as the scheme.
Huston, et al. Standards Track [Page 2]
RFC 8630 HTTPS TAL August 2019
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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.
1.2. Changes from RFC 7730
The TAL format defined in this document differs from the definition
in [RFC7730] in that:
o it allows for the use of the HTTPS scheme in URIs [RFC7230], and
o it allows for the inclusion of an optional comment section.
Note that current RPs may not support this new format yet.
Therefore, it is RECOMMENDED that a TA operator maintain a TAL file
as defined in [RFC7730] for a time as well, until they are satisfied
that RP tooling has been updated.
2. Trust Anchor Locator
2.1. Trust Anchor Locator Motivation
This document does not propose a new format for TA material. A TA 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 TA 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
TA to change, without needing to redistribute the TA per se.
In the RPKI, certificates contain one or more extensions [RFC3779]
that can contain a set of IP Address Delegations and/or Autonomous
System Identifier Delegations. In this document, we refer to these
delegations as the Internet Number Resources (INRs) contained in an
RPKI certificate.
The set of INRs associated with an entity acting as a TA is likely to
change over time. Thus, if one were to use the common PKI convention
of distributing a TA to RPs in a secure fashion, then this procedure
would need to be repeated whenever the INR set for the entity acting
as a TA changed. By distributing the TAL (in a secure fashion)
Huston, et al. Standards Track [Page 3]
RFC 8630 HTTPS TAL August 2019
instead of distributing the TA, this problem is avoided, i.e., the
TAL is constant so long as the TA'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 TA work, and the RPKI
implementor 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 TA URI as a URI that can be used to
retrieve a current TA certificate. This URI MUST be either an rsync
URI [RFC5781] or an HTTPS URI [RFC7230].
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, conforming to the restrictions defined
in Section 2 of [RFC5198], and ending with a line break,
2. a URI section that is comprised of one or more ordered lines,
each containing a TA URI, and ending with a line break,
3. a line break, and
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 TA Certificate Considerations
Each TA 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 TA in certification path discovery [RFC4158] and validation
[RFC5280] [RFC3779].
Huston, et al. Standards Track [Page 4]
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The validity interval of this TA is chosen such that (1) the
"notBefore" time predates the moment that this certificate is
published and (2) the "notAfter" time is after the planned time of
reissuance of this certificate.
The INR extension(s) of this TA 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 TA in the RPKI [RFC6480].
The public key used to verify the TA MUST be the same as the
subjectPublicKeyInfo in the CA certificate and in the TAL.
The TA MUST contain a stable key that does not change when the
certificate is reissued due to changes in the INR extension(s), when
the certificate is renewed prior to expiration.
Because the public key in the TAL and the TA MUST be stable, this
motivates operation of that CA in an offline mode. In that case, a
subordinate CA certificate containing the same INRs, or, in theory,
any subset of INRs, can be issued for online operations. This allows
the entity that issues the TA 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 TA MUST be published at a stable URI. When the TA is reissued
for any reason, the replacement CA certificate MUST be accessible
using the same URI.
Because the TA 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 TA, 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 TA URIs, the same self-signed
CA certificate MUST be found at each referenced location. In order
to increase operational resilience, it is RECOMMENDED that
(1) the domain name parts of each of these URIs resolve to distinct
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RFC 8630 HTTPS TAL August 2019
IP addresses that are used by a diverse set of repository publication
points and (2) these IP addresses be included in distinct Route
Origin Authorization (ROA) 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.
rsync://rpki.example.org/rpki/hedgehog/root.cer
https://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) TA, an
RP SHOULD:
1. Retrieve the object referenced by (one of) the TA 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 TA. These tests apply to the
validity of attestations made in the context of the RPKI relating
to all resources described in the INR extension(s) of this
certificate.
An RP SHOULD perform these functions for each instance of a 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 TA referenced by the TAL.
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RFC 8630 HTTPS TAL August 2019
In the case where a TAL contains multiple TA 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 TA. Some
examples are:
o Using the order provided in the TAL
o Selecting the TA 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. URI Scheme Considerations
Please note that the RSYNC protocol provides neither transport
security nor any means by which the RP can validate that they are
connected to the proper host. Therefore, it is RECOMMENDED that
HTTPS be used as the preferred scheme.
Note that, although a Man in the Middle (MITM) cannot produce a CA
certificate that would be considered valid according to the process
described in Section 3, this type of attack can prevent the RP from
learning about an updated CA certificate.
RPs MUST do TLS certificate and host name validation when they fetch
a CA certificate using an HTTPS URI on a TAL. RPs SHOULD log any TLS
certificate or host name validation issues found so that an operator
can investigate the cause.
It is RECOMMENDED that RPs and Repository Servers follow the Best
Current Practices outlined in [RFC7525] on the use of HTTPS
[RFC7230]. RPs 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 RPs 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 "*".
Huston, et al. Standards Track [Page 7]
RFC 8630 HTTPS TAL August 2019
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 TA private key permits unauthorized parties to
masquerade as a TA, with potentially severe consequences. Reliance
on an inappropriate or incorrect TA 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 TA 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.
RPs should either (1) have great confidence in the issuers of such
certificates that they are configuring as TAs or (2) issue their own
self-signed certificate as a TA and, in doing so, impose constraints
on the subordinate certificates.
6. IANA Considerations
This document has no IANA actions.
7. References
7.1. 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,
<https://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,
<https://www.rfc-editor.org/info/rfc3779>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
Huston, et al. Standards Track [Page 8]
RFC 8630 HTTPS TAL August 2019
[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
<https://www.rfc-editor.org/info/rfc5198>.
[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,
<https://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,
<https://www.rfc-editor.org/info/rfc5781>.
[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, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
February 2012, <https://www.rfc-editor.org/info/rfc6480>.
[RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for
X.509 PKIX Resource Certificates", RFC 6487,
DOI 10.17487/RFC6487, February 2012,
<https://www.rfc-editor.org/info/rfc6487>.
[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,
<https://www.rfc-editor.org/info/rfc7230>.
[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, <https://www.rfc-editor.org/info/rfc7525>.
[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,
<https://www.rfc-editor.org/info/rfc7730>.
Huston, et al. Standards Track [Page 9]
RFC 8630 HTTPS TAL August 2019
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in
RFC 2119 Key Words", BCP 14, RFC 8174,
DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/rfc8174>.
[X.509] ITU-T, "Information technology - Open Systems
Interconnection - The Directory: Public-key and attribute
certificate frameworks", ITU-T Recommendation X.509,
October 2016, <https://www.itu.int/rec/T-REC-X.509>.
7.2. 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,
<https://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,
<https://www.rfc-editor.org/info/rfc5914>.
[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,
<https://www.rfc-editor.org/info/rfc6486>.
Acknowledgements
This approach to TA 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 the 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.
Huston, et al. Standards Track [Page 10]
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Authors' Addresses
Geoff Huston
APNIC
Email: gih@apnic.net
URI: https://www.apnic.net
Samuel Weiler
W3C/MIT
Email: weiler@csail.mit.edu
George Michaelson
APNIC
Email: ggm@apnic.net
URI: https://www.apnic.net
Stephen Kent
Unaffiliated
Email: kent@alum.mit.edu
Tim Bruijnzeels
NLnet Labs
Email: tim@nlnetlabs.nl
URI: https://www.nlnetlabs.nl
Huston, et al. Standards Track [Page 11]