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According to this survey of block cipher modes (pp. 30-37), OFB mode is not SemCPA secure if the IV is a nonce, but "secure with a fixed sequence of IVs, like a counter." This responds to a subtle nuance in this paper: the security model that Rogaway uses allows nonces to be selected by the adversary, so the attacks shown against nonce-based OFB rely on such ...

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