4. Nelson produces budget encryption machines for people who cannot afford a full scale version of DES. The encryption consists of one round of a feistel system. The plaintext has 64 bits and is divided into a left hal left half A and a right hall ?. The encryption uses a function /( R) that takes an input string of 32 bits and outputs a string of 32 bits. ( There is no key, anyone naive enough to buy this system a key. ) The left hall of the ciphertext On h and the right hall is CUL D / R). Suppose Alice uses one of these machines to e Hand send a message to Bob. Bob has an identical use the machine to decrypt the ciphertex his decryption works (do not TUST e essentially justifying that