安全的电子邮件系统要实现加、解密、签名、认证等功能，而其中的一个核心问题是对密钥的管理，必须要有证书管理机关为用户签发和管理证书。ＰＧＰ和ＰＥＭ是目前广泛使用的安全的电子邮件系统和标准，但ＰＧＰ的密钥管理体制存在一定的缺陷，ＰＥＭ在实践中有基础设施和系统可缩放性方面的困难．本文在分析上述问题的基础上，提出了可缩放的层次ＣＡ结构，并实现了基本框架． A secure e-mail system to add, decrypt, sign, authentication and other functions, and one of the core issues is the key management, you must have a certificate authority for the user to issue and manage certificates. PGP and PEM are the most widely used and secure e-mail systems and standards. However, PGP’s key management system has some flaws. PEM has difficulties in infrastructure and system scalability in practice. Based on the analysis of the above problems, this paper proposes scalable hierarchical CA structure and realizes the basic framework.