| COSE Working Group | M. Jones |
| Internet-Draft | Microsoft |
| Intended status: Standards Track | March 11, 2019 |
| Expires: September 12, 2019 |
Additional Algorithm Registrations for COSE and JOSE
draft-jones-cose-additional-algorithms-00
The W3C Web Authentication (WebAuthn) specification and the FIDO2 Client to Authenticator Protocol (CTAP) specification use COSE algorithm identifiers. This specification registers algorithms in the IANA "COSE Algorithms" registry that are used by WebAuthn and CTAP implementations that are not already registered. Also, they are registered in the IANA "JSON Web Signature and Encryption Algorithms" registry, when not already registered there.
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This specification defines how to use several algorithms with COSE [RFC8152] that are used by implementations of the W3C Web Authentication (WebAuthn) [WebAuthn] and FIDO2 Client to Authenticator Protocol (CTAP) [CTAP] specifications. These algorithms are registered in the IANA "COSE Algorithms" registry [IANA.COSE.Algorithms] and also in the IANA "JSON Web Signature and Encryption Algorithms" registry [IANA.JOSE.Algorithms], when not already registered there.
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.
The RSASSA-PKCS1-v1_5 signature algorithm is defined in [RFC8017]. The RSASSA-PKCS1-v1_5 signature algorithm is parameterized with a hash function (h).
A key of size 2048 bits or larger MUST be used with these algorithms. Implementations need to check that the key type is 'RSA' when creating or verifying a signature.
The RSASSA-PKCS1-v1_5 algorithms specified in this document are in the following table.
| Name | Value | Hash | Description |
|---|---|---|---|
| RS256 | TBD (temporary assignment -257 already in place) | SHA-256 | RSASSA-PKCS1-v1_5 w/ SHA-256 |
| RS384 | TBD (temporary assignment -258 already in place) | SHA-384 | RSASSA-PKCS1-v1_5 w/ SHA-384 |
| RS512 | TBD (temporary assignment -259 already in place) | SHA-512 | RSASSA-PKCS1-v1_5 w/ SHA-512 |
| RS1 | TBD (temporary assignment -65535 already in place) | SHA-1 | RSASSA-PKCS1-v1_5 w/ SHA-1 |
This section defines algorithm encodings and representations enabling the Standards for Efficient Cryptography Group (SECG) elliptic curve "secp256k1" [SEC2] to be used for JSON Object Signing and Encryption (JOSE) [RFC7515] and CBOR Object Signing and Encryption (COSE) [RFC8152] messages.
The Standards for Efficient Cryptography Group (SECG) elliptic curve "secp256k1" [SEC2] is represented in a JSON Web Key (JWK) [RFC7517] using these values:
plus x and y values to represent the curve point for the key. Other optional values such as alg MAY also be present.
It is represented in a COSE_Key [RFC8152] using these values:
plus x (-2) and y (-3) values to represent the curve point for the key. Other optional values such as alg (3) MAY also be present.
The ECDSA signature algorithm is defined in [DSS]. Implementations need to check that the key type is EC for JOSE or EC2 (2) for COSE when creating or verifying a signature.
The ECDSA algorithm specified in this document is:
| JOSE Alg Name | COSE Alg Value | Description |
|---|---|---|
| ES256K | TBD (requested assignment -43) | ECDSA w/ secp256k1 Curve |
This section registers the following values in the IANA "COSE Algorithms" registry [IANA.COSE.Algorithms].
This section registers the following value in the IANA "COSE Elliptic Curves" registry [IANA.COSE.Curves].
This section registers the following value in the IANA "JSON Web Signature and Encryption Algorithms" registry [IANA.JOSE.Algorithms].
This section registers the following value in the IANA "JSON Web Key Elliptic Curve" registry [IANA.JOSE.Curves].
The security considerations on key sizes for RSA algorithms from Section 6.1 of [RFC8230] also apply to the RSA algorithms in this specification.
The security considerations on the use of RSASSA-PKCS1-v1_5 with SHA-2 hash functions from Section 8.3 of [RFC7518] also apply to their use in this specification. For that reason, these algorithms are registered as being "Not Recommended".
The security considerations on the use of the SHA-1 hash function from [RFC6194] apply in this specification. For that reason, the "RS1" algorithm is registered as "Deprecated". It MUST NOT be used by COSE implementations.
A COSE algorithm identifier for this algorithm is nonetheless being registered because deployed TPMs continue to use it, and therefore WebAuthn implementations need a COSE algorithm identifier for "RS1" when TPM attestations using this algorithm are being represented.
Care should be taken that a secp256k1 key is not mistaken for a P-256 key, given that their representations are the same except for the crv value.
The procedures and security considerations described in the [SEC1], [SEC2], and [DSS] specifications apply to implementations of this specification.
| [CTAP] | Brand, C., Czeskis, A., Ehrensvärd, J., Jones, M., Kumar, A., Lindemann, R., Powers, A. and J. Verrept, "Client to Authenticator Protocol (CTAP)", FIDO Alliance Proposed Standard, January 2019. |
| [IANA.COSE.Algorithms] | IANA, "COSE Algorithms" |
| [IANA.COSE.Curves] | IANA, "COSE Elliptic Curves" |
| [IANA.JOSE.Algorithms] | IANA, "JSON Web Signature and Encryption Algorithms" |
| [IANA.JOSE.Curves] | IANA, "JSON Web Key Elliptic Curve" |
| [WebAuthn] | Balfanz, D., Czeskis, A., Hodges, J., Jones, J., Jones, M., Kumar, A., Liao, A., Lindemann, R. and E. Lundberg, "Web Authentication: An API for accessing Public Key Credentials - Level 1", World Wide Web Consortium (W3C) Recommendation, March 2019. |
Thanks to John Fontana, Jeff Hodges, Tony Nadalin, Jim Schaad, Göran Selander, Wendy Seltzer, Sean Turner, and Samuel Weiler for their roles in registering these algorithm identifiers.
[[ to be removed by the RFC Editor before publication as an RFC ]]
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