Nonce
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Definition
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a value that is never reused with the same key — "number used once" — allowing a single long-term key to safely encrypt many messages
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How it enables key reuse safely
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a modern PRG takes both a seed (key) and a nonce ; the security guarantee only requires the pair to be unique, not alone — so can be reused as long as a fresh nonce accompanies every message
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Contrast with WEP's mistake
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WEP's IV was a nonce in spirit, but too short (24 bits, cycling quickly) and combined with the key in a way that produced related keys rather than independent-looking ones — see Two-Time Pad Attack
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