Assume that A and B share a long-term 256-bit AES key K. Our key exchange protocol has two goals: (1) let A and B agree on a new fresh session key Ks to be used for a current session, and (2) perform mutual authentication. Nb is a nonce and Ks is a new session key generated by B. Assume that Ks and Nb are of the same bit-length and both are always chosen at random. EK(.) denotes AES encryption of everything inside () with key K. HMACK(.) denotes SHA2-based HMAC of everything inside () using key K. Protocol:
1.A −→ B: EK(A, B, "Hello")
2.B −→ A: EK(Ks, Nb, HMACK(A, B, "Hello"))
3.A −→ B: HMACK(Ks, Nb, 1)
What (if any) are the vulnerabilities of this protocol? If there are any, how can you fix them? For fix, you need to show modification of the protocol. Limit each answer (vulnerabilities and their fixes separately) to 10 lines