Concurrent Signature Theory And Applied Research

As the rapid development of electronic commerce, electronic trading is increasingly integrating into daily life with unprecedented breadth and depth. However, the Internet itself is unsafe, so how to protect the fairness of the users becomes a new challenge. Fairness is a fundamental problem in exchange protocols, it means that at the end of exchange, either each party receives the expected item or neither party receives any useful information about the other's item. As one of the most important issues in cryptography, Fairness of digital signatures means that Participants which do not trust each other want to exchange their signatures in a fair way on the network. In recent years, there are many researches on fair exchange of digital signatures.Chen, Kulda, and Paterson first proposed the concept of Concurrent Signature, it was designed for the parties on the network which do not trust each other but need to exchange their digital signatures in a fair way, Concurrent signature provided (compared to the past) with a more feasible solution. For concurrent signature has unmatched good features than other signature schemes, it has good prospects in fair exchange of digital signatures and other e-commerce, it provide a fair way for the communicating parties to exchange their own signature on the message. In recent years, the international researches on concurrent signature are very active.In this paper, we first give the attack on an optimistic fair exchange protocols proposed by Changshe Ma, by security analysis, we find out it is insecure against cipher-text forgery attack. To deal with this defect, we proposed an improved scheme. Secondly, we construct a fair novel concurrent signature based on schnorr signature and segmentation technology to realize the fairness of both signers, the security of the scheme is related to the difficulty of solving the discrete algorithm problem. In our proposed scheme, the roles of two signers are equal, that is to say, our construction can achieve true fairness. In addition, because anonymity of ring signature make the signer cannot authenticate his own signature, so we construct a secure ID-based concurrent signature scheme based on ring signature. It is a scheme with self-authenticating which can authenticate that a signer possesses a signature's ownership.