Without public key cryptography, it is doubtful that there would be practical message security solutions, due to the fact that key management before public key cryptography was cumbersome.

• 如果没有公钥加密,那么是否存在实用的邮件安全解决方案是值得怀疑的,因为在公钥加密出现之前,密钥管理是一件很麻烦的事情。