A digital signature alone proves that a signed message is new and has never been replayed.

### Why this is right A signature can show that data was signed by the holder of a signing key and has not changed since signing, but the same valid signed message can be sent again. The signature alone does not establish freshness. ### The concept A replay attack occurs when an attacker resends a previously captured valid message. Preventing replay requires context that distinguishes a new communication from an old one, such as freshness information or protocol controls; the lesson’s signature workflow does not provide that by itself. Authenticity and integrity should not be confused with proof that a message is new. ### The other options - **True. A digital signature alone proves that a signed message is new and has never been replayed.**: This overstates what a signature establishes. A valid old signature can be replayed. ### Terms - **Replay attack**: Resending a previously captured message to try to make it accepted again. - **Authenticity**: Confidence that data came from the claimed source. - **Integrity**: Confidence that data has not been improperly altered. ### Watch out A valid signature can remain valid when an attacker resends the same old signed data. ### Remember A signature supports origin and integrity, not freshness by itself.