Question -his is your chance to break a cryptosystem. As we know by now, cryptography is a tricky business.

The subsequent problem illustrates how easy it is to turn a strong scheme into a weak one with minor modifications.

We saw in this chapter that key whitening is a good technique for strengthening block ciphers against brute-force attacks.

We now look at the given variant of key whitening against DES, which we'll call DESA:

DESAk,k1 (x) = DESk(x) XOR k1.

Even though the method looks similar to key whitening, it hardly adds to the security.

Your task is to show that breaking the scheme is approximately as difficult as a brute-force attack against single DES. Assume you have a few pairs of plaintext-ciphertext.

Solve this question and provide the answer as soon as possible.