On the security of the lee-hwang group-oriented undeniable signature schemes

Abstract

Undeniable signature is an intriguing concept introduced by Chaum and van Antwerpen at Crypto'89. In 1999, Lee and Hwang presented two group-oriented undeniable signature schemes with a trusted center. Their schemes are natural generalizations of Chaum's zero knowledge undeniable signature scheme proposed in 1990. However, we find that the Lee-Hwang schemes are insecure. In this paper, we demonstrate five effective attacks on their schemes: four of them are insider universal forgeries, in which one dishonest member (maybe colluding with a verifier) can get a valid signature on any chosen massage, and another attack allows a dishonest member to prevent honest members from generating valid signatures. We also suggest heuristic improvements to overcome some of the problems involved in these attacks. © Springer-Verlag 2004.