Let DES ( x, K ) represent the encryption of plaintext x with key K using the DES cryptosystem. Suppose y = DES ( x, K ) and y' = DES ( c ( x ) , c ( K )), where c ( * ) denotes the bitwise complement of its argument. Prove that y' = c ( y ). That is if we complement the plaintext and the key in DES, then the ciphertext also gets complemented. Note: This can be proved by the high level description of DES, the ac tual structure of S-Boxes or other component functions are irrelevant to this result.