Network security is essentially information security on the network, that is, the hardware, software and data of the network system are protected. It will not be destroyed, changed or leaked, the system will run reliably and normally, and the network service will not be interrupted. From the user's point of view, they hope that personal and business information will be protected by confidentiality, integrity and authenticity when transmitted on the network, so as to prevent others or opponents from using eavesdropping, impersonation, tampering, denial and other means to damage and infringe their own interests and privacy. From the point of view of network operators and managers, they hope to protect and control the access, reading and writing of local network information, avoid threats such as viruses, illegal access, denial of service and illegal occupation and control of network resources, and prevent and defend the attacks of network hackers.

According to its essential definition, network security should have the following basic characteristics: (1) confidentiality. Refers to the characteristics that information will not be leaked to or used by unauthorized individuals, entities and processes. All levels of the network system have different confidentiality and corresponding preventive measures. At the physical layer, it is necessary to ensure that system entities do not leak information by electromagnetic means. At the operational level, it is necessary to ensure that the system provides services according to the authorization, so that the system will not be used by unauthorized people at any time, such as hacker attacks, password attacks, illegal promotion of user rights, illegal use of resources, etc. (2) Integrity. Refers to the characteristics that information cannot be modified, destroyed, inserted, delayed, out of order and lost without authorization; (3) availability. Refers to the characteristics that legal users can access and use information in the required order, that is, to ensure that legal users can access information and related materials when needed.

In the physical layer, it is necessary to ensure that the information system can work normally in a harsh working environment. At the operational level, it is necessary to ensure that the system can always provide services for the licensor, ensure the availability of the system, and make the publisher unable to deny the published information content. The receiver can't deny the content of the received information, and uses digital signature to deny the data.