1. Suppose you are Eve, the eavesdropper. You intercept the following symbol of cyphertext: "L." You know that it was encrypted using the Caesar cypher, but you don't know the key. Enumerating all the keys, determine all the possible decryptions.
2. Now consider the use of the encryption function as the basis for a block cypher. That is, encrypt (or decrypt) each symbol of the plaintext separately. Suppose you, again Eve, intercept the following cyphertext which you know has been encrypted with a block cypher based on the Caesar cypher. Given that the cleartext is English text, how might you go about decrypting this message?
3. Suppose now that you have learned that the key is 17. What is the plaintext?
4. Assume you are using an alphabet that contains only four characters/symbols (Say, "A," "B," "C," and "D").
(a) How many different Caesar cyphers can be used with this alphabet? (i.e., how large is the keyspace?)
(b) How many different possible substitution keys exist for this alphabet?