Online Electronic Contracting System With The Trusted Third Party

Computer and net have taken great changes in recent decades, and these changes made the large-scale electronic commerce and trade systems having more security demands. The characteristics of the traditional business affairs such as security, creditable, unforgeable or unmodify, and can be arbitraged when any dissension occurred are all absolutely necessarily in the electronic commerce based on net and computer. The characteristics that the electronic files are easily copied and modified, the nets are interlinked and open make the electronic commerce not only more quick and easy but also insecurity. This thesis brings forward a new encryption algorithm and a digital signature algorithm that aim at the insecure factors. At the base of these algorithms we can realize the online electronic contracting.In this paper we firstly discuss the general concepts of compter security and cryptology, and then describe the mostly used modern encryption methods and technologies. We detail the advantages and disadvantages of symmetric algorithm, public-key algorithm and one-way hash function. At last we put forward a new block cipher - permutation code, and describe the secret hash digital signature and online electronic contracting with the trusted third party system. The secret hash digital signature is a new siganture method that combines the ideas of RSA public-key algorithm, MD5 one-way hash function and permutation code at the same time.