Suppose we are using a three-message mutual-authentication protocol, and Alice initiates contact with Bob. Suppose we wish Bob to be a stateless server, and it is therefore inconvenient to require him to remember the challenge he sent to Alice. Let us modify the exchange so that Alice sends the challenge back to Bob, along with the encrypted challenge. So the protocol is as shown in Figure 1. Is this protocol secure? Justify your answer.

l'm Alice kAB