Re: [webauthn] Mention fully-specified COSEAlgorithmIdentifiers in examples and recommendations (#2283)

> I will say that removing the restriction for `ESP*` IDs to allow them to be encoded as octet-key pairs (OKPs) [...]

COSE does not allow encoding `ESP*` keys with the OKP type. ECDSA public keys are required to use the EC2 key type; see [RFC 9053 §7.1. Elliptic Curve Keys](https://www.rfc-editor.org/rfc/rfc9053.html#name-elliptic-curve-keys) and [RFC 9053 §2.1. ECDSA](https://www.rfc-editor.org/rfc/rfc9053.html#section-2.1):

>When using a COSE key for this algorithm , the following checks are made:
>- The "kty" field MUST be present, and it MUST be "EC2".
>[...]

Only Edwards curve keys (currently) are allowed (and indeed required) to use OKP, and yes, [RFC 8032](https://www.rfc-editor.org/rfc/rfc8032.html) defines a single canonical encoding for EdDSA keys.

Rather, it's the EC2 key type that has two variants: compressed or uncompressed y coordinate.

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Received on Wednesday, 21 May 2025 10:13:53 UTC