4. ( 7 points) Consider a candidate cryptosystem that is used to encrypt a message m with key k where k is an integer chosen randomly between 1 and m2 and m denotes length of the message. If mi is the integer-mapped character i of the message, the ciphertext ci is derived via the following encryption algorithm: ci=2mi+k2 (a) How many different unique keys exist for this cryptosystem? (b) Can this scheme be broken using a brute force computational attack? Explain why or why not? (c) Write down the decryption algorithm. That is, show how mi is derived given ci and k. 4. ( 7 points) Consider a candidate cryptosystem that is used to encrypt a message m with key k where k is an integer chosen randomly between 1 and m2 and m denotes length of the message. If mi is the integer-mapped character i of the message, the ciphertext ci is derived via the following encryption algorithm: ci=2mi+k2 (a) How many different unique keys exist for this cryptosystem? (b) Can this scheme be broken using a brute force computational attack? Explain why or why not? (c) Write down the decryption algorithm. That is, show how mi is derived given ci and k