Tripartite concurrent signatures
Fair exchange in digital signatures has been considered as a fundamental problem in cryptography. The notion of concurrent signatures was introduced in the seminal paper of Chen, Kudla and Paterson in Eurocrypt 2004 Chen et al., 2004. In this paper, we partially solve an open problem proposed in Chen et al., 2004. We extend the notion of two party concurrent signatures to tripartite concurrent signature schemes. In tripartite concurrent signatures, three parties can exchange their signatures in such a way that their signatures will be binding concurrently. We present a model of tripartite concurrent signatures together with a concrete scheme based on bilinear pairings. It was noted in Chen et al., 2004 that extending concurrent signatures to a multi-party scheme, where there are three or more participants, cannot be achieved by trivially modifying their construction in Chen et al., 2004.