Therefore, the network security in not only related to
technique but also related to management. They are necessary
and complementary to each other. At present, the network
security is facing the new challenge of the man-made attack
and net-intrusion. In the information era, with the wide use of
computer network and the rapidly increasing demand of
information transmission, some enterprises got benefits for the
sake of the rapid, smooth network, yet some secret message
and data were attacked and damaged to a certain extent. The
attacking aims can be achieved by the following ways such as
stealing the password, eavesdropping the information,
tampering with the data, impersonating and denying the
signature. Some attackers even cancelled the important
database information, damaged the network nodes or spread
virus in the computer system.