________ thwart replay attacks by ensuring 'freshness' using cutoff values.

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

Answer: (A)

Freshness means making sure a message is current and not a replay of something seen before. Time stamps attach the moment the message was created, and the receiver checks that this timestamp falls within a defined cutoff window. If the stamp is too old or outside the window, the message is discarded. This windowed approach directly blocks replayed messages because an old transmission won’t be considered valid.

Nonces and sequence numbers also contribute to freshness, but they rely on different mechanisms (one-time random values or monotonic counters) and don’t inherently use a time-based cutoff window. The idea of using a cutoff to define what counts as “fresh” is most naturally implemented with time stamps, making them the best fit here.