GROUP-ORIENTED UNDENIABLE SIGNATURE SCHEMES WITHOUT A TRUSTED CENTER

Abstract

At Auscrypt'92, Harn and Yang firstly propose the concept of group-oriented undeniable signatures. Two threshold undeniable signature schemes were devised in their paper to realize the (1, n) and (n, n) cases. However, Langford in 1996 showed that Harn-Yang's (n, n) threshold undeniable signature scheme is not secure enough by presenting a conspiracy attack on it. Recently, Lin et al. also proposed a new (t, n) threshold undeniable signature scheme. Unfortunately, the Langford attack can be applied to Lin et al.'s scheme as well. Thus, the problem of designing a general group-oriented (t, n) threshold undeiable signature scheme is remained open. This paper will try to solve the open problem by proposing a general (t, n) threshold undeniable signature scheme without the assistance of a mutually trusted party. Moreover, this paper will extend the signing policy to the generalized case and propose a generalized group-oriented undeniable signature scheme.