COSE cryptographic algorithms - content key distribution

[pulsastrix]

#13 only adds a minimum subset of cryptographic algorithms for COSE structures.
The available algorithms should be expanded.

This issue lists the progress on the content encryption algorithms that we intend to support.

• Direct Encryption
  • Direct Key with KDF
    • direct+HKDF-SHA-256
    • direct+HKDF-SHA-512
    • direct+HKDF-AES-128
    • direct+HKDF-AES-256
• Key Wrap
  • AES Key Wrap (Add COSE structure extensions that allow use of predefined cryptographic backends + an OpenSSL based backend. #13)
    • A128KW (Add COSE structure extensions that allow use of predefined cryptographic backends + an OpenSSL based backend. #13)
    • A192KW (Add COSE structure extensions that allow use of predefined cryptographic backends + an OpenSSL based backend. #13)
    • A256KW (Add COSE structure extensions that allow use of predefined cryptographic backends + an OpenSSL based backend. #13)
• Direct Key Agreement
  • Direct ECDH
    • ECDH-ES + HKDF-256
    • ECDH-ES + HKDF-512
    • ECDH-SS + HKDF-256
    • ECDH-SS + HKDF-512
• Key Agreement with Key Wrap
  • ECDH with Key Wrap
    • ECDH-ES + A128KW
    • ECDH-ES + A192KW
    • ECDH-ES + A256KW
    • ECDH-SS + A128KW
    • ECDH-SS + A192KW
    • ECDH-SS + A256KW

Elliptic Curve support for the aforementioned key distribution algorithms:

• ECDH
  • X448
  • X25519