1 What is the most important difference between a symmetric key system and a public key system?

2 In what way does a hash function provide a better message integrity check than a checksum (such as Internet Checksum)?

3 Can you "decrypt" a hash of a message to get the original message? Explain.

4 Suppose that Bob receives a PGP message from Alice. How does Bob know for sure that Alice created the message?

5 Consider WEP for 802.11. Suppose that the data is 01010101 and the keystream is 11110001. What is the resulting ciphertext?

6. Using the monoalphabetic cipher in the textbook, encode the message "Computer is fun."

Decode the message "rmij'u uamu xyj."

7 Consider the RSA algorithm with p=5 and q=11.

a. What are n and z?
b. Let e be 3. Why is this an acceptable choice for e?
c. Find d such that de=1 (mod z) and d<160.