Alice and Bob use a block cipher for encryption and need to choose a mode of operation. Recall the..

Alice and Bob use a block cipher for encryption and need to choose a mode of operation. Recall the following two modes: • CBC mode: Here an n block plaintext M1M2 . . . Mn is encrypted to an n block ciphertext C1C2 . . . Cn using, Ci = EK(Mi ? Ci-1), i = 1, where C0 = IV . • Counter mode. Here an n block plaintext M1M2 . . . Mn is encrypted to an n block ciphertext C1C2 . . . Cn, where Ki = EK(IV ||i) Ci = Mi ? Ki , i = 1. An adversary is able to intercept and changes messages sent between Alice and Bob. Now consider the following scenarios. 1. In some messages sent by Bob, it is the case that the last block is a randomly generated secret key. Decide for the two modes whether the adversary can corrupt messages sent, so that Alice receives a message that looks good after decryption, but contains the wrong key