information and security plesse help

2. Consider a block encryption algorithm that encrypts blocks of n, and le N=2". Say we have : plaintext ciphertext pairs P,C=E(KP), where we assume that the key K selects one of the N! possible mappings. Imagine that we wish to find K by exhaustive search. We could generate key K' and test whether E(K',P) for 1 Sct. If K encrypts each P to its proper C, then we have evidence that K=K. However, it may be the case that mappings (K,-) and E(K'.-) agree on the plaintext-ciphertext text pairs P, C, but not on some of the other pairs. What is the probability that E(K,-) and E(K.) are in fact distinct mappings? (5 points)