a. Compute the Index of Coincidence IC for this sample.

b. What can you conclude about the length d of the key word used to encrypt the message? Explain your answer.

3. One hundred characters of ciphertext from a suspected Beaufort cipher were intercepted by one of your agents. Here is the frequency distribution of the letters of the alphabet in this sample of ciphertext: A B CD E F GH I J K L M 2 10 2 5 3 81 2 2 5 1 3 1 N O P Q R STUV W X Y Z 2 10 1 818 5 2 1 3 5 1 8 In other words, there are two As, ten Bs, etc., in the ciphertext