1、引言 计算机网络互联的发展几乎和计算机的发展一同起步。早在第一代(电子管)计算机时期,计算机通信网的研究工作便已开始。如今,不仅是计算机已成为信息处理中必不可少的工具,网络互联亦早已成为人类实现信息共享与交流的有力手段。 互联网的出现,使世界上原本千里之遥的两地瞬间变得近在咫尺。正因为如此,许多涉及国家军政、经济工商业情报以及一些私人数据等的敏感信息,越来越多地成 1, Introduction The development of computer network interconnection starts with the development of computer almost. As early as the first generation (tube) computer, research work on computer communications networks began. Nowadays, not only computers have become an indispensable tool in information processing, Internet has also become a powerful tool for human information sharing and exchange. With the advent of the Internet, the two places in the world, which were originally thousands of miles away, have become instantly accessible. It is for this reason that many sensitive information concerning national military and political affairs, economic and business intelligence as well as some personal data are increasingly becoming