Research On Key Techniques Of Non-repudiation Protocols

With the development of computer and communications technology, applications of Email and E-commerce are gradually entering all aspects of daily life. How to ensure fairness and privacy of the participating entities in information exchange is the current major concern. Non-repudiation protocols are just the key technology to solve such problems, it provide non-repudiation services for the participating entities, including non-repudiation of origin and non-repudiation of receipt. The design of Non-repudiation protocol must satisfies the fairness, timeliness, confidentiality and other security attributes. Therefore, our point in this thesis is to study the design of multi-party non-repudiation protocol and formal analysis of non-repudiation protocol. Our major achievements are as follows:A multi-party non-repudiation protocol supporting transparent off-line TTP is proposed. As a result of the using of transparent TTP, the privacy of the participating entity can be better protected. In addition, the protocol is an efficient scheme, and satisfies the fairness, timeliness and confidentiality.A self-adaptive multi-party non-repudiation protocol is proposed. The process of initializing the receiver set is added to the protocol and the encryption keys for different messages are XOR of the same key and a random number. Given the different initial parameters, the new protocol can be degraded to a multi-party non-repudiation protocol with same message or a multi-party non-repudiation protocol with different messages. In more general scenarios, the protocol can reduce the amount of public-key operations, reduce the burden of protocol entities, and therefore has a better efficiency.A multi-party non-repudiation protocol using key chains is proposed. The keys for encrypting messages in this protocol are the keys in a double key chain. In the case of multi-round message exchange, the trusted third party just keep a protocol session identifier and a group of entity identifier, it can effectively reduce the storage requirements of the trusted third party.An extended strand space method for fairness analysis of non-repudiation protocols is proposed. The method firstly introduce signature operation into strand space theory, redefine the set of terms and subterm relation in strand space theory. Then, the extended strand space model is constructed by inducing the action of protocols to the penetrator strand, the origin strand, the receiver strand and the trusted third party strand. Finally, the fairness of non-repudiation protocols can be analyzed by verifying that the existence of the origin strand in the bundle is equivalent to the existence of the receiver strand in the bundle depending on the measure of theorem proving. The analysis of the fairness of ZG protocol show that the proposed method can avoid state space explosion.