Network Working Group T. Bruijnzeels
Internet-Draft RIPE NCC
Intended status: Standards Track C. Martinez
Expires: May 17, 2018 LACNIC
November 13, 2017

RPKI signed object for TAL


Trust Anchor Locators (TALs) [RFC7730] are used by Relying Parties in the RPKI to locate and validate Trust Anchor certificates used in RPKI validation. This document defines an RPKI signed object [RFC6488] for a Trust Anchor Locator (TAL) that can be published by Trust Anchor to communicate a new TAL to already deployed Relying Parties. The two primary use cases for this are that 1) a Trust Anchor may wish to change the locations where its TA certificate may be found, and 2) a Trust Anchor may wish to perform a planned migration to a new key. Note that unplanned key rolls are considered out of scope for this document.

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Table of Contents

1. Requirements notation

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. Introduction

Trust Anchor Locator (TAL) files [RFC7730] are used in the Resource Public Key Infrastructure (RPKI) to help Relying Parties locate and verify a trust anchor certificate. A TAL file consists of:

The TAL can be distributed out-of-band to Relying Parties (RP), and it allows the RP to retrieve the most recent version of the Trust Anchor (TA) certificate from the cited location, and verify that public key of this certificate matches the TAL. This is useful as it allows selected data in the trust anchor to change, without needing to effect redistribution of the trust anchor per se. In particular the Internet Number Resources (INRs) extension [RFC3779] and the publication points defined in the Subject Information Access [RFC6487] may be updated this way.

The assumption is that both the URIs and key of the TA certificate remain stable. However, an organisation operating a TA may wish to change either of these properties, because of a need to:

In this document we describe a method for TA operators to publish a an updated TAL in a secure a well-defined fashion, so that RPs can be alerted about these changes.

Note that [RFC5011] describes Automated Updates of DNS Security (DNSSEC) Trust Anchors and can provide some useful insight here as well. However, concepts like a set of Trust Anchors, standby Trust Anchors, and TTLs are not applicable to the RPKI. Therefore we believe that an alternative approach based on already existing concept of the Trust Anchor Locator [RFC7730] is appropriate.

3. Signed TAL definition

A signed TAL is an RPKI signed object, as specified in [RFC6488]. The RPKI signed object template requires specification of the following data elements in the context of the manifest structure.

3.1. The Signed TAL Content Type

This document requests an OID for signed-Tal as follows:

signed-Tal OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
           rsadsi(113549) pkcs(1) pkcs9(9) 16 id-smime (1) TBD }

This OID MUST appear both within the eContentType in the encapContentInfo object as well as the content-type signed attribute in the signerInfo object (see [RFC6488]).

3.2. The Signed TAL eContent

The content of a Signed TAL is ASN.1 encoded using the Distinguished Encoding Rules (DER) [X.690], and is defined as follows:

SignedTalContent ::= IA5String

The "SignedTalContent" contains the content of the new TAL encoded in Base64 [RFC4648].

3.3. Signed TAL Validation

Before a Relying Party can use a Signed TAL, the relying party MUST first validate the Signed TAL. To validate a Signed TAL, the relying party MUST perform all the validation checks specified in [RFC6488] as well as the following additional specific validation step.

If the above procedure indicates that the manifest is invalid, then the Signed TAL MUST be discarded and treated as though no Signed TAL were present.

4. Signed TAL Generation

A TA MAY choose to generate a single Singed TAL object to publish in its TA certificate publication point(s) in the RPKI. The TA MUST perform the following steps to generate the Signed TAL:

5. Signed TAL Publication

A TA MAY publish a single Signed TAL object directly under its CA repository publication points. A non-normative guideline for naming this object is that the filename chosen for the signed TAL in the publication repository be a value derived from the public key part of the entity's key pair, using the algorithm described for CRLs in section 2.2 of [RFC6481] for generation of filenames. The filename extension of ".tal" MUST be used to denote the object as a signed TAL. Note that this is in-line with filename extensions defined in section 7.2 of [RFC6481].

6. Supporting a TA Key Roll

A Signed TAL MAY be used to communicate a planned key roll for the TA.

6.1. Preparing a new TA key

Prior to publishing the Signed TAL for the new key the TA MUST perform the following steps:

After these steps are performed a new Signed TAL MUST be generated as described in Section 4, and published as described in Section 5.

6.2. Staging period - Using both the old and the new TA key

The staging period is initiated by the initial publication of a Signed TAL for the new key and must be last at least 24 HOURS. During the staging period the TA MUST continue to operate both the old and the new TA key. Note that this is the same staging period used for key roll of normal CAs in the RPKI, described in [RFC6489].

6.3. Preserving the Signed TAL

The TA SHOULD preserve a Signed TAL for the old key after the staging period as a hint for RPs that missed the key roll. The following process can be used to achieve this:

6.4. Retiring the old key

The TA SHOULD retire and delete its old key after the staging period is over.

6.5. Relying Party Use

When an RP discovers a valid Signed TAL signed under a TA, and it notices that the contained TAL is different from its current TAL for this TA and that the "subjectPublicKeyInfo" has changed, then the RP MUST replace the TAL for this TA with the new TAL, abort the current top-down validation operation, and initiate a new top-down validation operation using the updated TAL.

It is RECOMMENDED that the software informs the operator of this event.

7. Supporting changing TA certificate publication point(s)

A signed TAL MAY be used to communicate an addition or removal of one or more publication locations where the TA certificate can be found.

7.1. Adding a publication point

When adding a publication point for a TA certificate, the TA MUST publish the certificate in the new location(s) prior to publication of the Signed TAL.

7.2. Withdrawing a publication point

When removing a publication point for TA certificate, the TA SHOULD observe a staging period of at least 24 Hours. The staging period is initiated by the publication of an updated Signed TAL where the publication point has been removed. During the staging period the TA SHOULD keep the old publication point up to date and available.

7.3. Publishing the Signed TAL

It is RECOMMENDED that a Trust Anchor publishes a valid Signed TAL for what it believes its current TAL should be at all times.

7.4. Relying Party Use

When an RP discovers a valid Signed TAL signed under a TA, and it notices that the contained TAL is different from its current TAL for this TA and that the "subjectPublicKeyInfo" has not changed, then the RP MUST replace the TAL for this TA with the new TAL for future use, but can continue the current top-down validation operation.

It is RECOMMENDED that the software informs the operator of this event.

8. IANA Considerations

8.1. OID

IANA is to add the following to the "RPKI Signed Objects" registry:

      Decimal  Description                       References

      TBD      signed-Tal                       [section 3.1]

8.2. File Extension

IANA is to add an item for the Signed TAL file extension to the "RPKI Repository Name Scheme" created by [RFC6481] as follows:

      Extension      RPKI Object           Reference
         .tal        Signed TAL            [this document]

9. Security Considerations


10. Acknowledgements


11. References

11.1. 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.
[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.
[RFC6481] Huston, G., Loomans, R. and G. Michaelson, "A Profile for Resource Certificate Repository Structure", RFC 6481, DOI 10.17487/RFC6481, 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.
[RFC6488] Lepinski, M., Chi, A. and S. Kent, "Signed Object Template for the Resource Public Key Infrastructure (RPKI)", RFC 6488, DOI 10.17487/RFC6488, February 2012.
[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.
[X.509] ITU-T Recommendation X.509 (2000), "Recommendation X.509: The Directory - Authentication Framework", 2000.
[X.690] ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002, "Information technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", 2002.

11.2. Informative References

[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC) Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011, September 2007.
[RFC6489] Huston, G., Michaelson, G. and S. Kent, "Certification Authority (CA) Key Rollover in the Resource Public Key Infrastructure (RPKI)", BCP 174, RFC 6489, DOI 10.17487/RFC6489, February 2012.

Authors' Addresses

Tim Bruijnzeels RIPE NCC EMail:
Carlos Martinez LACNIC EMail: