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I misunderstood the question You wrote your question in a way that the adversary sees only a single ciphertext. Therefore, OTP satisfies your definition but is not CPA secure. This is probably not what you had in mind. I think you should consider a definition where $\cal A$ outputs $(m_{1,0},m_{1,1}), (m_{2,0},m_{2,1}), \ldots, (m_{n,0},m_{n,1})$ and gets ...


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If a public-key encryption scheme is CPA-secure is it also secure in this revised version of CPA game? Yes, because this is essentially a trimmed down version of Left-or-Right-CPA security (PDF) which is provably equivalent to the first definition you mentioned which is also known as Find-Then-Guess-CPA security. If your scheme is LoR-CPA secure then you ...


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