You are conducting cryptanalysis to a symmetric cipher. You have access to the ciphertext in transit. You realize the secret key is not static but replaced with a new one periodically. Which of the following is the most likely effect you are facing because of the ever-changing secret key and ciphertext? (Source: Wentz QOTD)
B. Ciphertext-only attack
C. Chosen-ciphertext attack
Kindly be reminded that the suggested answer is for your reference only. It doesn’t matter whether you have the right or wrong answer. What really matters is your reasoning process and justifications.
My suggested answer is A. Confusion.
Confusion and diffusion are two properties of a cipher that can be used to measure its “quality.” A “perfect” cipher generates a completely different ciphertext even if only a single bit is changed in the secret key or plaintext. Confusion refers to how the alternation in the secret key will affect the ciphertext, while diffusion refers to the relationship between the plaintext and ciphertext.
The question is not asking about attack techniques.
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