0引言网络安全是传统的国界、领海、领空的三大国防和基于太空的第四国防之外的第五国防,称为Cyber-space。据美国FBI统计~([1]),美国每年网络安全问题所造成的经济损失高达75亿美元,而全球平均每20秒钟就发生一起Internet计算机侵入事件。网络安全不但涉及个人隐私、团体利益,更涉及社会稳定、经济安全、国家安全,是威胁人类和平发展的重大问题。局域网,简称LAN,是指在某一区域内(如1km左右)由多台计算机通过高速通信线路相连成的计算机组,是计算机网络 0 Introduction Cyber ​​security is the traditional national border, the territorial waters, the three major national territorial airspace and space defense beyond the Fourth Defense fifth defense, called Cyber-space. According to the U.S. FBI statistics ([1]), the annual economic losses caused by cyber-security problems in the United States are as high as 7.5 billion U.S. dollars. However, on average, every 20 seconds the world has witnessed Internet computer incursions. Network security involves not only individual privacy and community interests, but also social stability, economic security and national security. It is a major issue that threatens the peaceful development of mankind. LAN, or LAN for short, refers to a computer group connected by high-speed communication lines in a certain area (eg, about 1km). It is a network of computers