This problem deals with the protocol in Figure 9.17.

a) Show that this protocol is insecure. Hint: Let Trudy be the man-in-the-middle, and show that Trudy can convince Alice that she is Bob, and Trudy can determine Alice's session key K.

b) Slightly modify the protocol so that Trudy cannot obtain the session key

Figure 9.17 Mutual authentication and a session key