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The technological leap from isolated desktop systems to current systems integrated into local networks and Internet has added a new difficulty to the administrator's usual tasks: controlling system security.
Security is a complex field, which combines analysis techniques with techniques for detecting or preventing potential attacks. Such as the analysis of "psychological" factors, in relation to the behaviour of system users or attackers' possible intentions.
The attacks can come from many sources and affect from a single application or service or user to all of them or even the entire computer system.
Potential attacks can change the systems' behaviour and even make them crash (disabling them), or give a false impression of security, which can be difficult to detect. We can come across authentication attacks (obtaining access through previously disabled programs or users), interceptions (redirecting or intercepting communication channels and the data circulating within them) or substitution (replacing programs, machines or users for others, without the changes being noticed).
Example 9-1. Note
Absolute security does not exist. A false impression of security can be as damaging as not having any security. Security is a very dynamic field on which we need to keep our knowledge constantly updated.
We must bear in mind that it is impossible to achieve 100% security.
Security techniques are a double-edged sword that can easily give us a false impression of controlling the problem. Currently, security is an extensive and complex problem and, more importantly, it is also dynamic. We can never expect or say that security is guaranteed, but rather it will probably be one of the areas that the administrator will have to spend most time on and on which knowledge will have to be kept updated.
In this unit we will examine some of the types of attacks we can encounter, how we can verify and prevent parts of local security and network environments from being attacked. Furthermore, we will examine techniques for detecting intrusions and some basic tools that can help us to control security.
We should also mention that in this unit we can only introduce some of the aspects related to security nowadays. For any real thorough learning, we advise consulting the available bibliography, as well as the manuals for the products and tools we have covered.