But the e-mail system of the present mass use has natural security defects , so designing and realizing a safe e-mail system so as to ensure sensitive datum transferring becomes highly need urgently.

• 而目前的广泛使用的电子邮件系统具有天然的安全缺陷,因此如何设计并实现一个高度安全的电子邮件系统以保证敏感数据的非专用传送就成为网络安全领域中的迫切需要。