Let F:{0,1}n{0,1}n{0,1}n be a length-preserving pseudorandom function and a{0,1}n be a fixed n-bit string known to both Alice and Bob. They construct a private-key encryption scheme as follows. Gen: On input 1n, output a uniformly chosen key k of length n, i.e., output k{0,1}n. Enc: To encrypt a given message m{0,1}n, Alice computes Fk(a) and outputs the ciphertext as c=mFk(a). (a) Show Bob how to decrypt in the scheme . (b) Does the scheme have indistinguishable encryptions in the presence of an eavesdropper? Prove your answer. (c) Is the scheme CPA-secure? Prove your