RFC 7730

Resource Public Key Infrastructure (RPKI) Trust Anchor Locator

📅 published January 2016, from ietf

RFC 7730: Resource Public Key Infrastructure (RPKI) Trust Anchor Locator 💖

okay bestie, let's get the vibes right first 🦋 This is RFC 7730 from the Internet Engineering Task Force (IETF), filed in the Request for Comments series as Standards Track. It was published in January 2016 with ISSN 2070-1721 ✨ The authors are G. Huston (APNIC), S. Weiler (Parsons), G. Michaelson (APNIC), and S. Kent (BBN) 🫶 It obsoletes RFC 6490 🙈 and its header doesn't list any updates.

Abstract 🌸

So this doc defines a Trust Anchor Locator (TAL) for the Resource Public Key Infrastructure (RPKI). It 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.

Info about the current status of this document, any errata, and how to give feedback on it is at http://www.rfc-editor.org/info/rfc7730 🔥

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 ✨

Okay so this document defines a Trust Anchor Locator (TAL) for the Resource Public Key Infrastructure (RPKI) [RFC6480] 🧚 The TAL format can be used to distribute trust anchor material using a mix of out-of-band and online means. Procedures that Relying Parties (RPs) use to verify RPKI signed objects SHOULD support this format, because it makes interoperability between creators of trust anchor material and RPs way smoother 💖 And yes, this doc also obsoletes RFC 6490 by adding support for multiple URIs in a TAL.

1.1. Terminology 📚

Bestie, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be read as described in [RFC2119] 🤓

2. Trust Anchor Locator 🦋

2.1. Trust Anchor Locator Format 🎀

No new format for trust anchor material here, periodt 🙅 A trust anchor in the RPKI is a self-signed X.509 Certification Authority (CA) certificate. That's a format that's super common in PKIs and widely supported by RP software 💅 What this doc does specify is a format for the data used to retrieve and verify the authenticity of a trust anchor in a very simple way. That data is called the TAL ✨

The whole point of the TAL is to let selected data in the trust anchor change without needing to redistribute the trust anchor itself 🌸 In the RPKI, certificates carry extensions that represent Internet Number Resources (INRs) [RFC3779]. The set of INRs tied to an entity acting as a trust anchor is likely to change over time. So if you used the usual PKI move of handing a trust anchor to RPs in a secure fashion, you'd have to repeat that whenever the INR set for the trust anchor entity changed 😭 By distributing the TAL (in a secure fashion) instead of the trust anchor, this problem is avoided. In other words, the TAL stays constant as long as the trust anchor's public key and its location don't change 🫶

The TAL is kind of the lowkey cousin of the TrustAnchorInfo data structure from [RFC5914], which is on the Standards Track 👑 That spec could represent the TAL if someone defined an rsync URI extension for that data structure. But the TAL format was adopted by RPKI implementors before the PKIX trust anchor work, and the RPKI implementer community chose to use the TAL format instead of defining that extension. The community also likes the simplicity of the ASCII encoding of the TAL, versus the binary (ASN.1) encoding used 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. an rsync URI [RFC5781],
  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 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 because of changes in the INR extension(s), when the certificate is renewed before it expires, or for any reason other than a key change. Stable key or bust 😤

Because the public key in the TAL and the trust anchor MUST be stable, this motivates running that CA in an offline mode 🌙 So the entity that issues the trust anchor SHOULD issue a subordinate CA certificate that contains the same INRs (using the "inherit" option in the INR extensions of the subordinate certificate). This lets the issuing entity keep the private key of this certificate offline, while issuing all relevant child certificates under the immediate subordinate CA 🔒 It also means the Certificate Revocation List (CRL) that entity issues can be used to revoke the subordinate CA certificate if the online operational key pair, which is potentially more vulnerable, is suspected of being compromised 🚨

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 that same URI 🎯

Because the trust anchor is self-signed, there's no corresponding CRL that can revoke it, and there's no manifest [RFC6486] listing this certificate either. Not me being the odd one out 🙈

If an entity wants 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, the same self-signed CA certificate MUST be found at each referenced location. To boost operational resilience, it is RECOMMENDED that the domain name parts of each of these URIs resolve to distinct IP addresses used by a diverse set of repository publication points. These IP addresses should also be included in distinct Route Origin Authorizations (ROAs) objects signed by different CAs 🌈 That's the main character redundancy energy we love to see 👑

3. Relying Party Use 💅

Okay bestie, so this is how a Relying Party (RP) actually uses the TAL to grab and check a (putative) trust anchor 🫶. An RP SHOULD run through these steps:

  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 make sure the RP is willing to accept the entity publishing this self-signed CA certificate as 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 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 before the locally cached copy of the retrieved trust anchor referenced by the TAL expires. Don't let it expire on you 😭

Now here's the fun part: when a TAL has multiple URIs, an RP MAY use a locally defined preference rule to pick which URI it uses to retrieve the self-signed RPKI CA certificate that becomes the trust anchor. Some examples are:

  • Using the order provided in the TAL 📋
  • Selecting the URI randomly from the available list 🎲
  • 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 doesn't match the TAL public key, the RP SHOULD retrieve the CA certificate from the next URI, following the local preference ranking of URIs. Main character energy: always having a backup plan 💖

4. Security Considerations 🚨

Okay this part is seriously important, so listen up 👑 Compromise of a trust anchor private key lets unauthorized parties pretend to be a trust anchor, and the consequences can be severe 💀 Relying on an inappropriate or incorrect trust anchor has similarly severe consequences. Not okay!

This TAL does not directly provide a list of resources covered by the referenced self-signed CA certificate. Instead, the RP gets sent to the trust anchor itself and the INR extension(s) within this certificate. That gives necessary operational flexibility, but it also means the certificate issuer can claim to be authoritative for any resource 🙈 So relying parties should either have great confidence in the issuers of the certificates they configure 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. Choose your trust wisely, babe 🫶

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 thank Rob Austein and Randy Bush, who helped draft this document and gave super helpful review comments 🫶

The authors also give a shoutout to Roque Gagliano, Terry Manderson, and Carlos Martinez Cagnazzo for their work developing the ideas behind including 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
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