DEFINITION:

Network security consists of the policies, processes and practices adopted to prevent, detect and monitor unauthorized access, misuse, modification, or denial of a computer network and network-accessible resources. 

Network security involves the authorization of access to data in a network, which is controlled by the network administrator.

• Wikipedia

7.1. A MODEL FOR NETWORK SECURITY

A message is to be transferred from one party to another across some sort of internet. 

The two parties, who are the principals in this transaction, must cooperate for the exchange to take place. 

A logical information channel is established by defining a route through the internet from source to destination and by the cooperative use of communication protocols (e.g., TCP/IP) by the two principals. 

The general model shows that there are four basic tasks in designing a particular security service: 

1. Design an algorithm for performing the security-related transformation.

2. Generate the secret information to be used with the algorithm. 

3. Develop methods for the distribution and sharing of the secret information. 

4. Specify a protocol to be used by the two principles that makes use of the security algorithm and the secret information to achieve a particular security service. 

A general model is illustrated by the above Figure 1.6, which reflects a concern for protecting an information system from unwanted access. 

The hacker can be someone who, with no malign intent, simply gets satisfaction from breaking and entering a computer system. Or, the intruder can be a disgruntled employee who wishes to do damage, or a criminal who seeks to exploit computer assets for financial gain.