We consider a banking application, where messages m of the form fromAccount, toAccount, amount are sent within the bank network, with the meaning that amount dollars should be transferred from fromAccount to toAccount. Each message consists of three blocks, with each block holding one of the three parameters. Messages are encrypted using AES in Counter mode, i. e.Kj = E(K, Tj)Cj = Mj ⊕ KjEach of the three parts of a message is sixteen characters, i. e. one block, so messages consist of three blocks. a. The adversary has an account in the bank and can intercept and change messages. Imagine now that he knows the toAccount for a particular message m = C1C2C3. Explain how he can modify the message so that the amount is transferred to his own account. b. Explain how the use of a MAC would prevent this attack. c. Above, E(K, M) denotes using block cipher E with key K on message M. It is possible to define a cipher using similar ideas, but using a hash function instead. Describe how to do it, including how to decrypt.