There is one encryption algorithm called Affine Cipher, with encryption function E(x) = (ax + b) mod 26. Here, x is the numerical equivalent of the given plaintext letter, a and b are appropriately chosen integers. The numerical equivalents of the letters are as follows: A B C D E F X Y Z G H T J K L M N O P Q R S T U V W 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 0 1 2 3 a. Encrypt plaintext IT WILL BE DELIVERED TO YOU AT FIVE PM using affine function 7x + 9 mod 26. What is the decryption function? Show that it works. [10 marks] b. Consider an affine cipher (mod 26). You are doing a chosen plaintext attack using lalala and the cipher text is popopo. Determine the encryption function with explanation of the steps. [15 marks]