You may have noticed that there is a flaw in Figure 31.26. Eve, the intruder, can replay the third message and, if she can somehow get access to the session key, can pretend to be Alice and exchange messages with Bob. The problem can be avoided if both Alice and Bob use two nonces. Remember that nonces have a lifetime and their main purpose is to prevent replaying. Modify Figure 31.26 to add two nonces.