Walk into the lecture and title defense depth security model this is a strategy developed by the military.
The idea behind it is that instead of defeating an attacker with a single strong defensive line it's
better to weaken the attack by forcing the attacker to overcome successive barriers.
You spread out the security for example by doubling protective measures so that it covers a relatively
large space even if the first line of defense falls and even if the second follows the attack will become
noticeable and will lose momentum which will buy time to react appropriately.
The same strategy can be applied to computer systems as well.
Computer systems should be viewed in the way presented in the diagram on the right of the slide.
It presents a system based on independent function layers.
We will analyze each layer in detail later on.
Please note that every layer takes into account the human factor.
It's the most critical factor that affects security of the whole system.
People are very often the weakest link in the security of the system.
Users are susceptible to social engineering and manipulation.
We will now describe the defense and death model in more detail.
Let's try to illustrate it outside the world of computers.
Some medieval castles were surrounded by a moat.
The point was to make the enemy approach the barrier.
The castle was usually protected by one mode only such defenses weren't duplicated.
There was no point in doing that because if the enemy was able to defeat the barrier once they'd be
able to do it again.
Behind the moat there was a wall.
It was an additional barrier independent of the previous one.
Even if somebody managed to cross the moat they couldn't use the same strategy to climb up the wall.
The basis of the defense and depth model is that individual layers of security and solutions implemented
in each layer work independently of one another.
Having three different virus scanners is not exactly a defense in depth.
You can't assume that 3 scanners are better than one because if one doesn't detect a threat another
one will
three anti-virus scanners are just as effective as one defensins that requires installation of three
solutions independent of one another very often money is spent on duplicating security measures for
every layer of the system whereas each layer can be sufficiently protected by only one solution.
This is true also with regards to users.
We will analyze the model from top to bottom starting from data and application layers.
How can you secure data stored in computer systems
access control is the first solution.
This involves granting users access privileges.
The second solution which should be complementary to the first one is to prevent data loss by means
described in the service license agreement
this entails making backup copies or replicating data.
The next solution is to monitor data access you have to know who and when tried to read and modify the
data and whether they succeeded.
All in all data encryption is the only complete effective solution ensuring data confidentiality.
It makes the data independent of the system it's stored in and processed by
the first element of application layer protection is to regularly update your applications.
It will only be possible if the administrator knows every application running on the system.
This means he or she cannot allow users to install on their computers any application they want.
If you don't know something exists you won't try to update it.
Application updates are much more difficult to control than whole system updates.
It's hard to make it automatic.
The administrator has to remember to regularly update all applications
to implement the rules described above.
The administrator may prevent users from installing any kind of software
the administrator may introduce security measures that won't allow any user to install a certain program
this approach differentiates between allowed and forbidden programs.
It's a mechanism completely independent of user privileges.
Of course this layer should also be protected by anti-virus software.