CISSP – Information Systems Security Architecture Professional (ISSAP) — Question 45

Which of the following encryption modes can make protocols without integrity protection even more susceptible to replay attacks, since each block gets decrypted in exactly the same way?

Answer options

• A. Cipher feedback mode
• B. Cipher block chaining mode
• C. Output feedback mode
• D. Electronic codebook mode

Correct answer: D

Explanation

The correct answer is D, Electronic codebook mode, because it encrypts identical plaintext blocks into identical ciphertext blocks, making it easier for attackers to replay messages. The other modes, such as Cipher feedback mode, Cipher block chaining mode, and Output feedback mode, introduce variations in the ciphertext even for identical plaintext, which helps mitigate replay attacks.