| The rapid development of internet changes the people's life style, and the so-called information economy arise. Now people send or receive e-mail, do shopping and share information on the Internet. Private documents that in the past would have been committed to paper and hand-delivered are now routinely created, sent, and stored electronically. But the very things that allow such speed and ease of communication have also made it far more difficult to ensure one's privacy. In an electronic age, an interloper can intercept and alter message far more easily now than when face-to-face exchanges were the norm. As internet's wide application, people now pay more attention on the network security.The security of computer network includes confidentiality, authentication, integrity, availability and non-repudiation of information. Among them confidentiality is the base of network security. Encryption is usually applied to ensure confidentiality, so cryptography becomes very important to network security. We use block algorithm and public-key algorithm to design a security communication system named WinlDEA which can encrypt and transfer files such as text, photo, audio and application. And it can send or receive security e-mail.This article first analyzes the security of computer network, introduces basic technology that guarantee the security and emphasizes that cryptography is the core technology. Second chapter introduces the principle of computer cryptology, introduces several algorithms including DBS, IDEA and RSA. Third chapter explains the constitution and characteristics of WinlDEA. It describes the operations of the cipher algorithms. Fourth chapter explains the main modules of WinlDEA. Every module is based on MFC library. Base64 encoding is also introduced in this chapter. The public key is stored in a user information database which is built by Microsoft SQL Server 7.0. And the public key's security is guaranteed through SQL Server's security mechanism. In chapter five, it summarizes the successful aspects and shortages in the system. |
