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I have some questions from previous years exams, I hope you could help me with them. :)

Suppose that a protocol satisfies the properties of a $\Sigma$-protocol, except that it is only (plain) honest-verifier zero-knowledge. Show how to transform this protocol into a $\Sigma$-protocol for the same relation by assuming that the verifier generates $c \in C$ at random (with uniform distribution), where $(C,+)$ is an additive finite group.

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Are you using "an additive finite group" for "a group whose binary operation is $\hspace{1.7 in}$ written $\textbf{+}$" or "a quotient group of $\langle \mathbb{Z},+\rangle$"? $\;\;$ –  Ricky Demer Dec 4 '12 at 0:46
    
I think it is "a group whose binary operation is written +". –  Peter De Vries Dec 4 '12 at 0:54
    
What is your (or your lecturer's) definition of a Sigma-protocol? I'm presuming (s)he is including full ZK among the properties since the question mentions "only HVZK", is that what you're after? –  Bristol Dec 13 '12 at 14:02
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