Key management

The content key distribution methods of RFC 9053 §5 and §6, in Cose\Algorithm\KeyManagement: what fills a COSE_recipient on the sending side and reads one on the receiving side, to hand the layer below (the AEAD of a COSE_Encrypt, the MAC of a COSE_Mac, or the recipient above when recipients are nested) its key. RFC 9052 §8.5 sorts them into classes, and each class is an interface here, all extending KeyManagement: DirectEncryption (direct, direct+HKDF-*), KeyWrap (A128KW, A192KW, A256KW) and KeyAgreement (the twelve ECDH-*). The eighteen identifiers, with their classes, are listed in Key management algorithms; RSAES-OAEP (-40, -41, -42) and COSE-HPKE are not implemented.

EncryptStructure::encryptFor() runs the sending side for a whole message, see COSE_Encrypt; the receiving side is one call per recipient, the application picking the recipient that is its own.

• The two sides of an algorithm — what the sender computes and what the recipient computes
• What each family enforces — the rules of RFC 9052 §8.5 and RFC 9053 §6
• The KDF context — the COSE_KDF_Context and the parameters that fill it
• Key restrictions — the alg and key_ops checks of a recipient key