随着计算机网络的不断发展,全球信息化已成为人类发展的大趋势。但由于计算机网络具有联结形式多样性、终端分布不均匀性和网络的开放性、互连性等特征,致使网络易受黑客、恶意软件等的攻击,导致在网上公开的信息受到不同程度的破坏,所以网上信息的安全是一个至关重要的问题。无论是在局域网还是在广域网中,都存在着自然和人为等诸多因素的脆弱性和潜在威胁,故此,网络的安全措施应是能全方位地针对各种不同的威胁和脆弱性,这样才能确保网络信息的保密 With the continuous development of computer networks, the global informationization has become a general trend of human development. However, due to the diversity of connection forms, terminal distribution unevenness, network openness and interconnectivity, the network is vulnerable to attacks by hackers, malware and the like, resulting in varying degrees of damage to the public information on the Internet , So the safety of online information is a crucial issue. Both in the LAN and in the WAN, there are many factors such as natural and human vulnerability and potential threats, so the network security measures should be able to comprehensively address a variety of different threats and vulnerabilities, so as to ensure Confidentiality of network information