Public Key Infrastructure Pki-based Security E-mail System

In the age of Internet, email becomes an important communication way because of its convenience, efficiency and cheapness. Everyday, more and more enterprise and individual are sending and receiving information by email. However, there are some security problems in common used email system, for example: imitation, interruption and tampering, and repudiation. It discusses the cores of email protocols don't include any safety precautions to protect email from these threats. The unprotected mails are transmitted as plaintext that is easy to bring the divulging and tampering. Moreover, the password needed for authentication is also transmitted as plaintext when a connection to POP server is established, which may result in the stealing and divulging of the email. To solve these problems, secure email comes out.This thesis discuss the related protocols of email and applications of cryptography technologies for the mail protection after analyzing secure problems of traditional email, combines PKJ technique with S/MIME secure protocol and adopting the mixed cipher system, put forward achieving the fundamental frame of secure email following these protocols. According to this frame, carry through the system total design and the system detailed design, use some tool packages realize secure email system based on PKI.This system is a secure email system providing Digital Signature and Encryption, which has the following important characteristics: confidentiality, authentication, message integrity assurance, and non-repudiation of origin, it effectively solves several secure problems in traditional email system.