3 (20 points). The Cipher Block Chaining (CBC) mode for encryption is shown below Suppose Alice uses CBC to encrypt k plaintext blocks, let's call them P1,P2,..Pk into k Plaintext Plaintext Plaintext Initialization Vector (IV) Keyblock cipher encryption Keyblock cipher encryption Keyblock cipher eencryption Ciphertext Ciphertext Ciphertext Cipher Block Chaining (CBC) mode encryption a) If a hacker was able to tamper with few bits in the plaintext block P2, which resulted in an incorrect ciphertext C2. What happened to other ciphertext blocks? Can Bob correctly decrypt all the plaintext blocks correctly? If not, which of the plaintext blocks are affected by the tampering? b) Suppose now that the hacker changes few bits in the ciphertext C2 only during transmission, i.e., the encryption result for C2 is correct but it was changed during transmission over the network. This means that the receiver Bob receives incorrect value of C2. How many blocks does this affect during the decryption at the receiver? 3 (20 points). The Cipher Block Chaining (CBC) mode for encryption is shown below Suppose Alice uses CBC to encrypt k plaintext blocks, let's call them P1,P2,..Pk into k Plaintext Plaintext Plaintext Initialization Vector (IV) Keyblock cipher encryption Keyblock cipher encryption Keyblock cipher eencryption Ciphertext Ciphertext Ciphertext Cipher Block Chaining (CBC) mode encryption a) If a hacker was able to tamper with few bits in the plaintext block P2, which resulted in an incorrect ciphertext C2. What happened to other ciphertext blocks? Can Bob correctly decrypt all the plaintext blocks correctly? If not, which of the plaintext blocks are affected by the tampering? b) Suppose now that the hacker changes few bits in the ciphertext C2 only during transmission, i.e., the encryption result for C2 is correct but it was changed during transmission over the network. This means that the receiver Bob receives incorrect value of C2. How many blocks does this affect during the decryption at the receiver