Exercise 4. Bob is arguing that if you use Electronic Codebook (ECB) mode twice in a row to encrypt a long message, M, using the same key each time, that it will be more secure. Explain why Bob is wrong in the case of using a binary one-time pad encryption scheme. solution online

ECB gives same result for the same data hence it is of no use to encrypt same message by using ECB.

Explanation:

Electronic Codebook (ECB) is used to encrypt data and give ciphertext for the same. When the same message is encrypted by using ECB twice or more times, it gives the same result again and again.

So, when Bob Uses ECB twice to encrypt a long message M, it will give the same ciphertext twice which is of no use.

Hence, Bob is wrong in the given scenario.