Definitions

Nonce is

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[a] value used in security protocols that is never repeated with the same key. For example, challenges used in challenge-response authentication protocols generally must not be repeated until authentication keys are changed, or there is a possibility of a replay attack. Using a nonce as a challenge is a different requirement than a random challenge, because a nonce is not necessarily unpredictable.[1]

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“

[a] random or non-repeating value that is included in data exchanged by a protocol, usually for the purpose of guaranteeing the transmittal of live data rather than replayed data, thus detecting and protecting against replay attacks.[2]

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References