An attack where an adversary intercepts an encrypted message and transmits it again later is called a ________.

• A. Replay attack
• B. Reflex attack
• C. Reflection attack
• D. Resend attack

Answer: (A)

Intercepting a valid encrypted message and sending it again later is a replay attack. The attacker isn’t changing the message or forging new credentials; they’re simply reusing something that was already valid to trick the recipient into acting on it again—often to gain unauthorized access or repeat a transaction. The key defense is ensuring freshness: include nonces, timestamps, or sequence numbers, and verify them so the same message can’t be accepted as new. This is what prevents a replay from succeeding, even if the ciphertext remains perfectly valid.

Other terms describe different patterns. A reflection or reflexive pattern involves the system echoing or bouncing back a request or response, not necessarily reusing a captured message at a later time. A resend notion isn’t a standard term for this scenario, and it doesn’t capture the security flaw of replaying a prior valid message.