I. Let the 26 letters have the numerical values A = 0, B = 1, , Z = 25 Write plaintext as M nomi and ciphertext as C = ac- where the m, and c are letters of the alphabet. Recall that the Vigenre cipher (after Blaise de Vigenre) with key word K-kki..k-1 enciphers m with the formula c (mki mod t) mod 26 and deciphers ci with the formula mi = (ci-k(i mod t)) mod 26 The Beaufort cipher (after English Admiral Sir Francis Beaufort, but invented earlier by Giovanni Sestri) is similar to the Vigenre cipher in that it has a key word of length t letters. The Beaufort cipher enciphers the i-th plaintext letter mi with the formula c, -(ki mod t) - m) mod 26 a. Encipher the plaintext ATTACKATDAWN using the Beaufort cipher with key word KEY. b. Write the formula used by the Beaufort cipher to decipher the i-th ciphertext letter c