An Optimistic Non-repudiation Protocol Focused on Transparent Trusted Third Party

Non-repudiation service is widely employed in information exchange and online transaction. It requires that its participants are unable to deny their involvement in specific protocol. At the same time, the service should keep fairness, which means that no one could take any advantages over the other one. Researchers have introduced a trusted third party (TTP) to realize these demands. Protocols are grouped into several categories according to the degree of TTP´s involvement in protocols. Optimistic non-repudiation protocol is the most important method undoubtedly owe to its lower TTP´s involvement. There are two questions. One is that whether it is possible to further decrease TTP´s involvement or not. A computable optimistic non-repudiation protocol seems to be a good improvement. This is also our paper´s basic protocol. The other question is about whether two types of finally evidences that produced by participants (here is Alice and Bob, and we denote this type evidences as the first type evidences) and TTP (or with the help of TTP, and we demote this type evidences as the second type evidences) are identical. If both types of evidences are not exactly the same, then it shows that TTP has taken part in process of protocol. Thus, it is certain that either participants behaved dishonest, or network went wrong. Participants´ prestige will be negatively affected more or less. On the contrary, if two types of evidences are identical, then such feelings will be eliminated. This kind of TTP is called transparent TTP. In this paper, we have accomplished an optimistic non-repudiation protocol with the help of transparent TTP based on a computable non-repudiation protocol.