5. (10 points) (a) Give the formulas for CBC mode encryption and decryption (b) Suppose that Alice encrypts plaintext blocks Po, P , Pn using CBC mode to obtain the corresponding ciphertext blocks, Co, Ci,...Cn, which she sends to Bob, along with the corresponding initialization vector (IV). During trans- mission, Trudy changes block Ci to, say, X. Which blocks decrypt correctly? Show your work. (c) Suppose that Alice computes a MAC on plaintext blocks 1, P , . . . , B,. she then sends Bob the plaintext, along with the IV and the MAC. During trans- mission, Trudy changes block P to, say, Y. Show that Bob will almost certainly detect the change. 5. (10 points) (a) Give the formulas for CBC mode encryption and decryption (b) Suppose that Alice encrypts plaintext blocks Po, P , Pn using CBC mode to obtain the corresponding ciphertext blocks, Co, Ci,...Cn, which she sends to Bob, along with the corresponding initialization vector (IV). During trans- mission, Trudy changes block Ci to, say, X. Which blocks decrypt correctly? Show your work. (c) Suppose that Alice computes a MAC on plaintext blocks 1, P , . . . , B,. she then sends Bob the plaintext, along with the IV and the MAC. During trans- mission, Trudy changes block P to, say, Y. Show that Bob will almost certainly detect the change