Resource Public Key Infrastructure (RPKI) Trust Anchor Locator
obsoleted by
- rfc-7730 — Resource Public Key Infrastructure (RPKI) Trust Anchor Locator
Extracted elements (19)
The TAL format was chosen over TrustAnchorInfo (RFC 5914) because RPKI implementors adopted TAL prior to the PKIX trust anchor work, the community preferred its simplicity, and no rsync URI extension was defined for TrustAnchorInfo. The ASCII encoding of TAL was also preferred over the binary ASN.1 encoding.
The TAL was introduced to allow selected trust anchor data (specifically Internet Number Resources) to change without requiring redistribution of the trust anchor certificate itself. The TAL remains constant as long as the trust anchor's public key and location do not change.
The TAL format was adopted by RPKI implementors prior to the PKIX TrustAnchorInfo (RFC 5914) standard. Rather than defining an rsync URI extension for TrustAnchorInfo, the RPKI community elected to retain the simpler ASCII TAL format.
An RP SHOULD perform TAL validation for each TAL instance every time it performs re-synchronization across the local repository cache, and also prior to expiration of the locally cached copy of the retrieved trust anchor.
Because the trust anchor key must be stable, the issuing entity SHOULD operate that CA in off-line mode and SHOULD issue a subordinate CA certificate containing the same INRs via the 'inherit' option. This keeps the trust anchor private key off-line while allowing normal issuance under the subordinate CA.
If an entity wishes to withdraw a self-signed CA certificate as a trust anchor for any reason, including key rollover, the entity MUST remove the object from the location referenced in the TAL.
Procedures used by Relying Parties to verify RPKI signed objects SHOULD support the TAL format to facilitate interoperability between creators of trust anchor material and RPs.
The INR extension(s) of the trust anchor MUST contain a non-empty set of number resources and MUST NOT use the 'inherit' form of the INR extension(s).
The object referenced by the TAL's rsync URI MUST be a self-signed CA certificate that conforms to the RPKI certificate profile (RFC 6487). This certificate serves as the trust anchor in certification path discovery and validation.
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 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 trust anchor MUST be published at a stable URI. When reissued for any reason, the replacement CA certificate MUST be accessible using the same URI.
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 renewed prior to expiration, or for any reason other than a key change.
The validity interval of the trust anchor SHOULD reflect the anticipated period of stability for the particular set of INRs associated with the trust anchor.
To use a TAL, an RP SHOULD: retrieve the object at the TAL URI; confirm it is a current self-signed RPKI CA certificate conforming to RFC 6487; confirm the public key in the TAL matches the retrieved object; and perform any additional locally-appropriate checks.
A Trust Anchor Locator (TAL) is a data structure combining an rsync URI pointing to a self-signed RPKI CA certificate and the Base64-encoded subjectPublicKeyInfo of that certificate. It enables retrieval and authenticity verification of the trust anchor.
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 carries similarly severe risks.
The TAL does not directly provide a list of resources covered by the referenced self-signed CA certificate; the RP is referred to the trust anchor's INR extensions. This operational flexibility also allows the certificate issuer to claim authority over any resource, so RPs must either have great confidence in the issuer or issue their own constrained self-signed trust anchor.
A 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 encoded in Base64 (RFC 4648 Section 4). The format is ASCII text.