Replay attacks can be thwarted by using ________.

• A. Time stamps
• B. Sequence numbers
• C. Nonces
• D. All of the above

Answer: (D)

Replay attacks rely on resending a valid message to trick the system, so protocols use freshness checks to prove a message isn’t a reused copy. Time stamps embed the sending time, letting the receiver reject messages outside an acceptable window if clocks are reasonably synchronized. Sequence numbers attach a monotonically increasing value to each message, so duplicates or old numbers can be detected and dropped. Nonces introduce a one-time value in a challenge–response, ensuring a captured reply isn’t usable again in the same session. Each method provides a different angle on freshness, and combining them strengthens protection across different scenarios. That’s why all of the above is the best answer.