| Summary: | 碩士 === 國立中央大學 === 資訊工程研究所 === 96 === With the growth of electronic commerce, issues of guaranteeing fairness between the transactors through the Internet is more and more important and the protocol of transactions should avoid any involved party to take advantage of other parties via improper behavior. Hence, the research on fair exchange protocols was extensively developed in the last twenty years. But in early works, the fairness relies on the assumption that either both parties have comparable computing power or a trusted third party is involved.
The concept of concurrent signature was introduced by Chen, Kudla, and Paterson at Eurocrypt 2004. A concurrent signature attempts to provide the similar functionality of a fair exchange without assuming the existence of a trusted third party or comparable computing power of the two parties. In the Chen-Kudla-Paterson scheme, the signatures signed by the two parties remain ambiguous
until the additional information {em keystone} is released.
The previous scheme only handles two participants in a transaction. At ISC 2006, Tonien, Susilo, and Safavi-Naini proposed the first multi-party concurrent signature scheme. In this thesis, it will be pointed out that the multi-party concurrent signature scheme proposed by Tonien {it et al.} does not achieve the goal of a concurrent signature. Furthermore, a fair multi-party concurrent
signature scheme will be proposed. It not only achieves the goal of a concurrent signature but also provides a fairer property and flexibility in a transaction.
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