1.Implement the attacks described in this chapter for the shift cipher and the Vigenre cipher.

2. Show that the shift, substitution, and Vigenre ciphers are all trivial to break using a chosen-plaintext attack. How much chosen plaintext is needed to recover the key for each of the ciphers?

3. Assume an attacker knows that a user's password is either abcd or bedg. Say the user encrypts his password using the shift cipher, and the attacker sees the resulting ciphertext. Show how the attacker can determine the user's password, or explain why this is not possible.