Which of the following controls would BEST protect against internet sniffers conducting a replay attack?

Question

Options

• APacket-filtering router
• BDigital signature
• CProperly configured firewall
• DTime-stamped data encryption

• A
  3% (1)
• B
  6% (2)
• C
  9% (3)
• D
  82% (27)

Explanation

Time-stamped data encryption directly defeats replay attacks by embedding a timestamp within each encrypted message, so any captured packet retransmitted after the valid time window is automatically rejected as stale - the encryption also prevents the attacker from altering the timestamp to extend its validity.

Why the distractors fail:

• A (Packet-filtering router): Filters by IP/port/protocol, but a replayed packet looks identical to a legitimate one - it passes through undetected.
• B (Digital signature): Proves authenticity and integrity, but a captured legitimately signed message can still be replayed; the signature remains valid on retransmission. (Signatures need pairing with nonces or timestamps to stop replay.)
• C (Properly configured firewall): Controls access by rules, but has no mechanism to distinguish a fresh packet from a replayed copy of one that was already allowed through.

Memory tip: Think "Time kills replay" - a timestamp makes captured traffic expire like a coupon with a past-due date, rendering the replay useless.

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