Paper 2003/007

A Price Negotiable Transaction System

Huafei Zhu

Abstract

We present a practical protocol that allows two players to negotiate price over the Internet in a deniable way so that a player $A$ can prevent another player $B$ from showing this offer $P$ to a third party $C$ in order to elicit a better offer while player $B$ should be sure that this offer $P$ generated by $A$, but should $C$ be unclear whether $P$ is generated by $A$ or $B$ itself, even $C$ and $B$ fully cooperated. Our protocol is a standard browser-server model and uses a trusted third party, but only in a very limited fashion: the trusted third party is only needed in the cases where one player attempts to cheat or simply crashes, therefore, in the vast of majority transactions, the third party is not to be involved at all. In addition, Our price negotiable transaction system enjoys the following properties: \begin{description} \item[(1)]It works in an asynchronous communication model. \item[(2)]It is inter-operated with existing or proposed scheme for electronics voting system; \item[(3)]The two players need not sacrifice their privacy in making use of the trusted third party; \item[(4)]The deniable property can be proved secure in the random oracle paradigm, while the matching protocol can be proved secure in the standard intractable assumption. \end{description}