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Question: for nbit block size there are 2quot possible plaintext blocks...

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For n-bit block size, there are 2 possible plaintext blocks and 2 possible ciphertext blocks. If the plaintext or ciphertext is represented by an integer, then its value ranges from 0 to 2-1. a. How many different n-bit block to n-bit block mappings are there? b. How many different reversible n-bit block to n-bit block mappings are there? plock mapping is used as a key for the substitution, then what would its minimum bit-len be? [Hint: If there are 64 keys altogether, then each key can be represented by log:(64)- 8 bits. This is the minimum bit length. class we considered the representation of a reversible 4-bit mapping that was a 4 x 24 64-bit string (we took this as the key). How much shorter is the (minimal) key length computed in (c) when n-4?

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