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cosec >students >Teaching >Winter 2008/2009 

Toward a Generic Construction of Universally Convertible Undeniable Signatures from Pairing-Based Signatures

Laila El Aimani (cosec - b-it)

Thursday 20 November 2008, 15.00, b-it  1.25 (cosec meeting room)

Undeniable signatures were proposed to limit the verification property of ordinary digital signatures. In fact, the verification of such signatures cannot be attained without the help of the signer, via the confirmation/denial protocols. Later, the concept was refined to give the possibility of converting the issued undeniable signatures into ordinary ones by publishing a \emph{universal} receipt that turns them publicly verifiable.

In this paper, we present the first generic construction for universally convertible undeniable signatures from certain weakly secure cryptosystems and any secure digital signature scheme. Next, we give two specific approaches for building universally convertible undeniable signatures from a large class of pairing-based signatures. These methods find a nice and practical instantiation with known encryption and signature schemes. For instance, we achieve the most efficient undeniable signatures with regard to the signature length and cost, the underlying assumption and the security model. We believe these constructions could be an interesting starting point to develop more efficient schemes or give better security analyses of the existing ones.

\textbf{Keywords: } Undeniable signatures, Pairing-based signatures, Generic construction.

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