A Fair Transaction Protocol with an Offline Semi-Trusted Third Party

Trusted Third Party (TTP) must be completely trustworthy when it is used in a transaction protocol to achieve fairness. But in previous works, most of the proposed protocols depend on certain strong assumptions about the third party trust, not considering possible misbehaviors by the third party and conspiracy within the main parties to some extent. In this paper, a fair transaction protocol using an offline STTP (semi-trusted third party) is proposed, which is based on the idea of RBAC(Role-Based Access Control). In the novel protocol, STTP also avoids misbehaviors on its own or conspiracy with either of the main participants by adopting interactive validation signature protocol. Meanwhile, the proposed protocol is analyzed for its security and efficiency. The results of the analysis show that it not only provides improved security, but also features high efficiency and practicability.