Clarifying RPKI use of CMS SignerInfo"

RFC 6485 defines The Profile for Algorithms and Key Sizes for Use in the Resource Public Key Infrastructure (RPKI). In that document, Section 2 specifies a single signature algorithm (SHA-256) and a single CMS OID, sha256withRSAEncryption, to be used for the SignerInfo field of the CMS object. A closer reading of the relevant RFCs RFC 4055 and RFC 5754 identified that the CMS SignerInfo field must support use of the rsaEncryption OID for full conformance with the CMS specifications, and the normative references in RFC 6485 inherit the requirement. To ensure full conformance with the CMS specifications, RFC 6485 is updated by this draft. All of RFC 6485 applies except for a change to the SignerInfo field.

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 RFC 2119.

In RFC 6485 Section 2 the following sentence: The Object Identifier (OID) sha256withRSAEncryption from [RFC4055] MUST be used. Is replaced by: One of the Object Identifiers (OID) rsaEncryption or sha256WithRSAEncryption from [RFC4055] MUST be used. RPKI implementations MUST support rsaEncryption for the signatureAlgorithm field and SHOULD support sha256WithRSAEncryption.

All known RPKI CA implementations already do what this draft recommends.

Andrew Chi and David Mandelberg discovered this problem. Russ Housley documented the RFC chain back to 2630. This draft reflects a discussion between Rob Austein and Matt Lepinski on the SIDR Working group mailing list and a private communication between Rob Austein and Geoff Huston.

This memo includes no request to IANA.

By conforming more closely to the CMS specifications, RPKI CMS objects are less likely to be rejected as non-conformant with the standards. No change is made to the cryptographic status of the CMS objects produced.