FUNDAMENTALS OF COMPUTER

Detailed explanation-1: -DES with any number of rounds fewer than 16 could be broken with a known-plaintext attack more efficiently than by a brute-force attack. This explains the “Why not less than 16". As for the “why not more than 16", that is a tradeoff for speed of execution (more rounds = less speed).

Detailed explanation-2: -The DES algorithm uses a key of 56-bit size. Using this key, the DES takes a block of 64-bit plain text as input and generates a block of 64-bit cipher text.

Detailed explanation-3: -Data Encryption Standard (DES) is a block cipher algorithm that creates plain text in blocks of 64 bits and transform them to ciphertext using keys of 48 bits. It is a symmetric key algorithm, which defines that the similar key is used for encrypting and decrypting information.

Detailed explanation-4: -The round-key generator uses 17 permutation operations: one parity drop and 16 compression permutation operations for each round. 5. The total number of exclusive-or operations is 16 × 2 = 32, because each round uses two exclusive-or operations (one inside the function and one outside of the function). 6.