最後，我們的系統不僅保留了謝等人系統的特性，也克服了黃等人所發現的缺陷。而且我們的系統不只可以達到更好的效能與公平性，同時也是我們認為目前最有效率的系統。 ;The increasing popularity of the Internet promotes the quick growth of electronic commerce in the recently years. More and more business transactions are accomplished through the Internet because of its convenience and efficiency. Therefore, issues of guaranteeing transactions fairness becomes important, especially when the transactors are mutually distrustful.
The concept of concurrent signatures aims to provide a practical solution to the fair exchange problem without relying on a trusted third party or the assumption of the same computing power between two transactors. After proposed the fi rst concurrent signature, the authors were questioned about whether their notion can be extended to multi-party setting. Tonien et al. were the first ones who tried to answer the question. But Tonien et al.′s scheme was pointed out by Shieh et al. that it failed to achieve the concurrent notion and an alternative scheme was proposed. Unfortunately, a defect of Shieh et al.′s scheme was pointed out by Huang et al. by providing a strong while unproven claim of the infecundity of designing a multi-party concurrent signature.
Although Shieh et al.′s scheme is insufficient to be truly fair in the multi-party setting, it is still a good lesson to be learned for our research. This thesis analyses underlying schemes and reconsiders the design of multi-party concurrent signatures. After that, we proposed an improved scheme based on Shieh et al.′s design to achieve the required fairness requirement, which means that there is still possibility to design a concurrent signature for the multi-party setting. Our improved scheme is not only secure against the defect pointed out by Huang et al. but it also keeps all the features of Shieh et al.′s scheme. Furthermore, the proposed scheme achieves better performance and fairness. As a result, our scheme seems to be the most efficient concurrent signature scheme so far as we know.
