Research On Cryptographic Technologies In Electronic Cash System

With rapid development of Internet, electronic commerce has become a wide area of internet applications. E-payment is a crucial process in electronic commerce and its security has attracted more and more people's focus. Due to the merits of anonymity and being off-line, off-line electronic cash system has become the hotspot in the research of e-payment. Meanwhile, the design and analysis of secure and efficient electronic cash schemes is gaining increasing importance of the international academia.Beginning with the analysis of status quo of the e-commerce both home and abroad, the thesis points out that the lack of secure and efficient e-payment has become a common difficulty which all the counties around the world are facing in the process of developing e-commerce. After a comprehensive comparison between e-check, credit card based e-payment and e-cash, the thesis clarifies that e-cash is the most suitable means for e-commerce at present. Then the status quo and history of the research on e-cash and the basic theory of e-cash have been discussed with much detail.Partially blind signatures allow a signer to explicitly include necessary information (coin value, expiration date, or whatever) in the resulting signatures under some agreement with the receiver. With partially blind signature, the bank has to neither change his public key to represent a new expiration date, nor use different public keys for different coin values. The stress of storage is alleviated tremendously for the bank only needs to store the valid records which are before their expiration dates. The thesis extends the partially blind WI-Schnorr signature scheme and proposes a partially blind signature scheme called Protocol P, which can combine with the TTP mechanism to implement anonymity control. Then the thesis strictly proves that Protocol P is partially blind and witness indistinguishable.Based on Protocol P, the thesis proposes a secure and fair off-line e-cash protocol and adds a role of trusted third party in the protocol to realize anonymity revocation on special occasion. Combining wallets with observers with partially blind signature, the thesis proposes a secure and fair off-line e-cash protocol which guarantees prior restraint of double-spending, while still offering traceability of double-spenders after the fact in case tamper-resistance is compromised. The security of the e-cash protocol has been analyzed as well. It realizes all the principal functions of e-cash systems, and sets up a solid foundation for the practical utility of e-cash. In the end, the thesis anticipates the prospect of the research and development of e-cash.