3. (10 points) Alice encrypts a message with key K using a stream cipher. She sends the resulting cipher-text C (1000, 1011, 0110, 1011) to Bob. Suppose that Trudy is.able.to intercept the ciphertext and she knows that the plaintext for this message is P = (1011, 0001, 0101, 1100). (a) Recover the keystream Ks (b) Show how Trudy can use the keystream Ks from part a to produce the ciphertext C, where D(C, K) will yield the plaintext P (0001, 1101, 1001, 0000)