please provide correct solution.

Suppose we use the following authentication protocol for the server Bob to authenticate a user Alice. Alice initiates contact with Bob. Suppose we wish Bob to be a stateless server, and therefore it is inconvenient to require him to remember the challenge he sent to Alice. Hence, Alice is required to send the challenge back to Bob, along with the encrypted challenge. So the protocol is: Is this protocol secure? (We do not consider database reading attack here.)