Assume that A and B share a long-term 256-bit AES keyK. Our key exchange protocol has twogoals: (1) let A and B agree on a new fresh session keyKsto be used for a current session, and (2)perform mutual authentication. Nb is a nonce andKsis a new session key generated by B. AssumethatKsandNbare of the same bit-length and both are always chosen at random. EK(.) denotesAES encryption of everything inside () with keyK. HM ACK(.) denotes SHA2-based HMAC ofeverything inside () using keyK Required:
What (if any) are the vulnerabilities of this protocol?