Undeniable signature has been extensively researched after Chaum and Antwerpen first proposed the concept of this special digital signature ten years ago. Up to now, however, almost all the existed schemes are based on discrete logarithm cryptosystems. In this paper, based on an improvement of the practical threshold RSA signature scheme proposed by Shoup at Eurocrypt'2000 and the first undeniable RSA signature scheme proposed by Gennaro, Krawczyk and Rabin at Crypto'97, we present the first, as we know, threshold undeniable RSA signature scheme. Our scheme is secure and robust since all the partial signatures are verifiable by adopting a discrete logarithm equality protocol proposed by Shoup.
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