1. For n-bit block size, there are 2ⁿpossible plaintext blocks and 2ⁿpossible ciphertext blocks. If the plaintext or ciphertext is represented by an integer, then its value ranges from 0 to 2ⁿ 1.
2. 1. How many different n-bit block to n-bit block mappings are there?
   2. How many different reversible n-bit block to n-bit block mappings are there?
   3. If a reversible n-bit block mapping is used as a key for the substitution, then what would its minimum bit-length be? [Hint: If there are 64 keys altogether, then each key can be represented by log₂(64) = 8 bits. This is the minimum bit length.]
3. 4. In class, we considered the representation of a reversible 4-bit mapping that was a 64-bit string (that was the key length). How much shorter is the key length computed in c. when n=4?