An avalanche effect is also desirable for the key: A one-bit change in a key should result in a dramatically different ciphertext if the plaintext is unchanged. Assume an encryption with a given key. Now assume the key bit a position 1 (prior to PC - 1) is being flipped. Which S-boxes in which rounds are affected by the bit flip during DES encryption? Which S-boxes in which DES rounds are affected by this bit flip during DES decryption