Fair Exchange of Signatures with Multiple Signers

Abstract

Chen et al. introduced a new notion of a concurrent signature scheme for a fair exchange of signatures with two parties. Chen et al. also proposed a concrete scheme and proved its security under the assumption of discrete logarithm problem. Recently, Hiwatari and Tanaka extended the concept of concurrent signature to many-to-one setting. Hiwatari and Tanaka also proposed a concrete scheme; however, it requires some strong assumption to achieve the fair exchange and it is not efficient. This paper gives another construction of concurrent signature for many-to-one setting with multisignature scheme. Hereafter, we call it (n,1) concurrent signature scheme. The proposed scheme is more efficient than the scheme of Hiwatari and Tanaka in computation complexity and signature size, and achieves the fair exchange without the assumption required for the scheme of Hiwatari and Tanaka. This paper also gives a construction for the fair exchange of signatures in many-to-many setting, called (n,m) concurrent signature scheme, in appendix.