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Erschienen in:
2007 | OriginalPaper | Buchkapitel
Gradually Convertible Undeniable Signatures
(Michels-Petersen-Horster Convertible Undeniable Signatures Revisited)
verfasst von : Laila El Aimani, Damien Vergnaud
Erschienen in: Applied Cryptography and Network Security
Verlag: Springer Berlin Heidelberg
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In 1990, Boyar, Chaum, Damgård and Pedersen introduced
convertible undeniable signatures
which limit the self-authenticating property of digital signatures but can be converted by the signer to ordinary signatures. Michels, Petersen and Horster presented, in 1996, an attack on the Elgamal-based seminal scheme of Boyar
et al.
and proposed a repaired version without formal security analysis. In this paper, we modify their protocol so that it becomes a generic one and it provides an advanced feature which permits the signer to universally convert
achronously
all signatures pertaining to a specific time period. We supply a formal security treatment of the modified scheme: we prove, in the generic group model, that the protocol is existentially unforgeable and anonymous under chosen message attacks, assuming new assumptions (though reasonable) on the underlying hash function.