3.1.5.3 HomeGroup Credentials and Signing Key Messages
Whenever a HomeGroup Credentials message or a HomeGroup Signing Key message is received, its encrypted fields MUST be decrypted using the Encryption Key (section 3.1.4.5.1) with the AES-256 algorithm [FIPS197] in Cipher Block Chaining mode [SP800-38A] with a zero Initialization Vector (IV).