1. Every day, Alice sends an encrypted message to Bob, her stockbroker. On some days the plaintext of the message is simply the date and time and "No action today"; on other days the message has the date and time followed by instructions to buy or sell a quantity of the stock of the company where Alice works. Charlie is able to obtain a copy of every email Alice sends, but he is unable to decrypt any of them. Briefly explain how traffic analysis might enable Charlie to take advantage of Alice's "insider trading". (For this review we will not consider the legal or ethical issues regarding the actions of any person involved.)

2. Alice and Bob frequently communicate in an online "chat room". One day, Charlie conducts a successful man-in-the-middle attack against their online chat. Briefly explain what Charlie must achieve for this attack to be successful.