Name:______________________________     Alpha:________________________________ 

1. [8pts] Fill out the table by giving the right cryptographic schemes.

   	private key	public key
   data confidentiality
   data integerity

2. [2pts] TRUE/FALSE

   In a private key encryption scheme, Alice and Bob should share the same key before exchanging encrypted messages with each other.

3. [5pts] What is the difference between the known plaintext attack and the chosen plaintext attack?

4. [5pts] What is the difference between the chosen plaintext attack and the chosen ciphertext attack?

5. [10pts] Consider the following ciphertext (shown in a hex string form).

   a3890567e9cb50d0754627

   The OTP scheme with the following key was used to create this encryption.

   ebec690b86eb07bf072a43

   What is the message? (You may want to write a simple script for this).

6. [5pts] Consider the following message-ciphertext pair.

   message:     b'IT430 Rocks!'
   ciphertext:  b'\xbeM\x90\x9c{}a/OVW\x93'
   

   In fact, the message and the ciphertext have the same length -- 12 bytes long. Why does the ciphertext look longer?

7. [10pts] As we discussed from class, the known-plaintext attack breaks the OTP scheme if the same key is reused to encrypt different messages. Consider the following plaintext-ciphertext pair (now in the bytes form)

   message:     b'IT430 Rocks!'
   ciphertext:  b'\xbeM\x90\x9c{}a/OVW\x93'
   

   Crack the following ciphertext. What is the message for this ciphertext?

   ciphertext:  b'\xb0v\x84\xe1*+Ja\r\x1c\x05\x93'
   

   message: