As we have seen, MACs can be used to authenticate messages.With this problem, we want to show the difference between two protocols—one with a MAC, one with a digital signature. In the two protocols, the sending party performs the following operation:

1. Protocol A: y = ek1 [x||h(k2||x)] where x is the message, h() is a hash function such as SHA-1, e is a private-key encryption algorithm, "||" denotes simple concatenation, and k1, k2 are secret keys which are only known to the sender and the receiver.

2. Protocol B: y = ek[x||sigkpr (h(x))] Provide a step-by-step description (e.g., with an itemized list) of what the receiver does upon receipt of y. You may want to draw a block diagram for the process on the receiver’s side, but that’s optional