Optimistic fair-exchange protocols based on DSA signatures

The problem of fair exchange is a fundamental problem in secure electronic transactions and digital rights management. Park et al. (2003) presented an optimistic fair-exchange protocol based on RSA. Dodis and Reyain (2003) analyzed the vulnerability of Park´s scheme and presented an optimistic fair-exchange protocol based on GDH. This paper point out that Dodis and Reyain´s scheme is also insecure and inefficient. This work presents a multisignature scheme based on DSA, and describes a novel method of constructing very efficient fair-exchange protocols based on improved DSA signatures. The protocols in this paper are more secure and efficient.