Consider the following message authentication code: H: {0, 1}* {0, 1}n H(m) = = m mod k where k is an n-bit secret. (n is say 120 so you can't simply guess k) a. Can you easily forge a MAC tag for some messages? Which messages can you do this for? b. Give the best chosen-message attack that can think of that breaks the MAC (finds the secret key k). Be sure to include the complexity of the attack.