COSEKey

COSEKey refers to the COSE_Key data structure used in the COSE (CBOR Object Signing and Encryption) framework. It provides a portable, CBOR-encoded representation of cryptographic keys that can be used with COSE messages such as signing, verification, encryption, and decryption.

A COSE_Key is encoded as a CBOR map containing a mandatory key type field (kty) and a collection of key-specific parameters. The map may also include optional metadata, such as a key identifier (kid) and algorithm constraints (alg). The exact parameters depend on the key type and can describe public keys, private keys, or symmetric keys.

Key types include:

- EC2: elliptic-curve keys for ECDSA or related algorithms, with parameters such as crv (curve identifier), x and y coordinates, and possibly d for the private key.

- OKP: octet key pair used for EdDSA schemes, with parameters such as crv and x, and possibly d.

- Symmetric: shared secret keys for symmetric algorithms, with the parameter k representing the key value.

A COSE_Key can be transported as part of COSE structures, such as COSE_Sign, COSE_Sign1, COSE_Encrypt, or COSE_Decrypt, and can include usage constraints or key management data via standard fields like kid or alg.

Standardization and references: COSE_Key is defined in RFC 8152, within the COSE specification set. The format is intended to be interoperable across COSE implementations and CBOR-based cryptographic material.