Analysis and Improvements of Two Identity-Based Perfect Concurrent Signature Schemes

Abstract

The notion of concurrent signatures was introduced by Chen, Kudla and Paterson in their seminal paper in Eurocrypt 2004. In concurrent signature schemes, two entities can produce two signatures that are not binding, until an extra piece of information (namely the keystone) is released by one of the parties. Upon release of the keystone, both signatures become binding to their true signers concurrently. In ICICS 2005, two identity-based perfect concurrent signature schemes were proposed by Chow and Susilo. In this paper, we show that these two schemes are unfair. In which the initial signer can cheat the matching signer. We present a formal definition of ID-based concurrent signatures which redress the flaw of Chow et al.'s definition and then propose two simple but significant improvements to fix our attacks.

Adaptively Secure Threshold Signature Scheme in the Standard Model

“…We say that G is a bilinear group if it satisfies these requirements. In recent years, many cryptographic schemes were proposed based on some computational hard problems in the bilinear groups (Boneh et al, 2001;Boldyreva, 2003;Boneh and Boyen, 2004;Qian et al, 2005;Waters, 2005;Wang et al, 2005;Long et al, 2006;Lu et al, 2006;Xu, 2006;Kancharla et al, 2007;Huang et al, 2007;Chang et al, 2007;Tseng et al, 2008). The security of our scheme relies on the hardness of the Computational Diffie-Hellman (CDH) problem in the bilinear groups.…”

Improved Fair Exchange Protocol Based on Signcryption-Based Concurrent Signature

“…However, Wang et al [11] pointed out the schemes in [7] are not fair, and actually they are more favorable to the initial signer, so Wang et al provided two improved perfect concurrent signature schemes. Recently, Chow et al [12] and Huang et al [13] respectively developed ID-based perfect concurrent signature schemes, and [14] proposed a certificate-based perfect concurrent signature scheme.…”