MAC values can be used to authenticate messages. Also, digital signature can be used for the same purpose. Below are two protocols for authentication, one using MAC and the other using digital signature. In these protocols x message, h () hash function, || The concatenation symbol, E is a symmetric encryption algorithm, k1 and k2 are only the secret keys of the sender and receiver, Sig is a digital signature algorithm, and Kpr is the sender's private key.

a) For both protocols, explain step by step the steps to be taken for authentication on the receiving side.

b) Compare these two approaches in terms of performance.

Protocol A: y=Eki ( x || h(k2 || x)) Protocol B: y=Eki ( x || SigKpr( x ))