目前企业面临的计算环境和过去有很大的变化，许多数据资源能够依靠网络来远程存取，而且越来越多的通讯依赖于公共网络公共网络（如 Internet），而这些环境并不保证实体间的安全通信，数据在传输过程可能被其它人读取或篡改。-currently facing the enterprise computing environment and past a great change, many data resources to be able to rely on remote network access, and more and more dependent on public communications networks public networks (such as the Internet), which environment is not a guarantee of the security entities communications, data transmission possible by other people read or tampered with.