In the textbook the four basic modes of operations of block ciphers (ECB, CBC, OFB, CFB) are…

In the textbook the four basic modes of operations of block ciphers (ECB, CBC, OFB, CFB) are analyzed with respect to error propagation in encryption. That is, the consequences on ciphertext blocks by changing a single plaintext block are discussed. a) For all four modes of operation analyze the effect on the decryption of remaining blocks if for the sequence of ciphertext blocks c1, c2, . . . , cn some ciphertext block cj is errorness, 1 = j < n. That is, specify which of plaintext blocks xj , xj+1, xj+2, . . . , xn are recieved correctly. b) One of the recommendations for a proper use of “One-time pad” (to ensure perfect secrecy) is to never reuse the same key for encryption of two different messages. The simplest way to implement “One-time pad” is to generate a random key sequence of the same length as message and to encrypt using, Ci = Mi + Ki (mod 26), where Ki are random key characters and M = K = C =Z26. Explain how only the knowledge of two different ciphertext sequences C = C1C2 · · · Cn and C 0 = C 0 1C 0 2 · · · C 0 n , obtained by applying 5 the same secret key, can compromize the security of the system.