Use definition 2 of perfect secrecy (Lemma 2.4 of the textbook) to prove that the Vigenre cipher is not perfectly secret. Pr[Enck (m) = c) = Pr[Enck (m') = c] (2.1) Lemma 2.4. An encryption scheme (Gen, Enc, Dec) with message space M is per- fectly secret if and only if Equation (2.1) holds for every m, m' E M and every