【作者】 肖春芸；

【导师】 何大可；

【作者基本信息】 西南交通大学 ， 计算机应用技术， 2002， 硕士

【摘要】 Internet最基本，也是最重要的服务，就是电子邮件。随着Internet的进一步发展，电子邮件作为一种通信方式逐渐普及。当前，电子邮件的用户已经从科学和教育行业发展到了普通家庭中的用户，电子邮件传递的信息也从普通文本信息发展到包含声音、图像在内的多媒体信息。随着电子邮件应用的不断深入，用户越来越重视电子邮件系统的安全性、稳定性、收发速度等指标。 本论文分析了电子邮件系统面临的安全威胁，给出了增强电子邮件系统安全性的措施，详细讨论了基于PKI的S／MIME协议和SASL验证机制在安全电子邮件系统中的实现。论文同时分析了现有的电子邮件系统传输编码存在的缺陷，描述了一种编码效率高、数据扩展率低的数字数据变换方法：基数-91编码，将该编码方法应用到电子邮件系统，可以明显提高邮件传输速度。 作者研究了电子邮件的一系列协议，在完全遵循相关标准的基础上，设计并开发了一个独立的、支持基数-91编码的安全电子邮件客户端软件。该软件除了实现常规收发电子邮件功能之外，重点增加了电子邮件的加密、数字签名、身份认证、完整性检查等诸多安全性功能。更多还原

【Abstract】 Electronic mail (Email) is one of the most important services in Internet. With the rapid development of Internet, Email has become a popular communication tool. Nowadays, the users of Email come from not only the scientific and educational professions but also ordinary family. Information transmitted by Email expands from common textual information to multimedia information including audio and video. With the further application of Email, the users pay more and more attention to such indexes as the security, stability and transmission speed of the Email system.This paper analyzes the menace that Email system faces and proposes effective solutions to enhance its security. What’s more, the paper does a detailed discussion on how to implement the S/MIME protocol based on PKI and SASL authentication mechanism in secure Email system. Meanwhile the paper analyzes the deficiency of current transmission coding and describes a new digital transformation method, base91 encoding, with high encoding efficiency but low data extension. This method can obviously improve the transmission speed when used in electronic mail system.After the investigation of the related protocols of Email, the author developed a kind of secure Email agent software based on the international standards, which can support base91 encoding. Besides having the traditional function of receiving and sending Email, the software puts great emphasis upon providing the secure services of confidentiality, authentication, integrity, non-repudiation and so on.更多还原