5. For a bit string A, let A denote the complementary string obtained by changing all the 1s to 0s and all the 0s to 1s (equivalently, A = A 11111...). Show that if the DES key K encrypts x to y, then K encrypts x to y, i.e., if y = DES K (x), then y = DES K (x). Hint: This has nothing to do with with the structure of the S-boxes. All you need to do is to work through the encryption algorithm.