Local Networks and the Internet: From Protocols to Interconnection

Chapter 17

Security

17.1. Risks

Although the Internet allows us to have fast access to a large quantity of information or to exchange e-mails, the interconnection to a network where any access control is implemented creates some risks. The information systems always contain design failures. A hacker can uses this to authorize the consultation, modification or destruction of a company’s internal documents. Following this section, we show some of the risks linked to information security in Unix environments.

Passwords are the reinforcements most often used to protect access to systems or documents. If a hacker knows the user name, he or she can try to guess the password by logging on to the computer. This type of attack takes a relatively long period of time. For instance if the hacker can get direct access to the file with these passwords, he or she can discover them faster in his or her system.

In Unix computers, the passwords are coded using an irrevocable algorithm before being stored on the hard disc. It is difficult to find the original from of the coded value. When a user logs on, the password given is automatically coded and compared to the stored value. This principle, apparently safe, led Unix designers to leave the coded password file available for everybody to access. Unfortunately, computer power having increased, it is now possible using brute force (e.g. testing all the words in the dictionary), to find the simplest passwords. The new version of Unix has corrected ...