Problem 2. (33 points) (a - 23 points) Remember the Needham Schroeder protocol. The protocol has a weakness when an old session key K, shared by A and B is compromised. That is, assume the attacker M gets hold of an old session key K. M can then launch a successfull attack. All he has to do is to capture A's message to B in step 5: EB(K, A) Then, using knowledge of the old key K and the above message, M can contact B (in the Needham Schroeder protocol) and pretend to be A. Show how this can be done, through the sequence of steps of the attack. (b - 10 points) Show how to use timestamps to prevent this attack. Problem 2. (33 points) (a - 23 points) Remember the Needham Schroeder protocol. The protocol has a weakness when an old session key K, shared by A and B is compromised. That is, assume the attacker M gets hold of an old session key K. M can then launch a successfull attack. All he has to do is to capture A's message to B in step 5: EB(K, A) Then, using knowledge of the old key K and the above message, M can contact B (in the Needham Schroeder protocol) and pretend to be A. Show how this can be done, through the sequence of steps of the attack. (b - 10 points) Show how to use timestamps to prevent this attack