Let X ^’ be the bitwise complement of X. prove that if the complement of the plaintext block is taken and the complement of an encryption key is taken, then the result of DES encryption with these values is the complement of the original cipher text. That is,

If Y = E(K, X)

If Y ^’ = E(K ^’ , X ^’ )

Hint: Begin by showing that for any two bit strings of equal length, A and B, (A ⊕ B) ^’ = A ^’ ⊕B. It has been said that a brute-force attack on DES requires searching a key space of 2 ⁵⁶ keys. Does the result of part (a) change that?

Answer rating: 100% (QA)

For example if we take the plaintext message 8787878787878787 and encrypt it with the DES key 0E3292... View the full answer