Wireless Security.pdf - PDF Archive

Security Defined 211
9.2 What Can We Do?
In the face of all these adversities, what can we do to make the system less vulnerable?
We will look at the basics of computer security from a general level to familiarize the
reader with the concepts that will be reiterated in the chapters to come. Even more
experienced readers may find this useful as a review before delving into the specifics of
network and Internet security.
9.3 Access Control and the Origins of Computer Security Theory
In their seminal computer security paper, “ The Protection of Information and Computer
Systems, ” (Saltzer 1976), Saltzer and Schroeder recorded the beginning concepts of
access control, using the theory that it is better to deny access to all resources by default
and instead explicitly allow access to those resources, rather than attempt to explicitly
deny access rights. 2 The reason for this, which may be obvious to you, is that it is
impossible to know all the possible entities that will attempt access to the protected
resources, and the methods through which they gain this access. The problem is that it
only takes one forgotten rule of denial to compromise the security of the entire system.
Strict denial to all resources guarantees that only those individuals or organizations given
explicit access to the resources will be able to have access. The system is then designed
so that access to specific resources can be granted to specific entities. This control of
resources is the fundamental idea behind computer security, and is commonly referred to
as access control .
Over the years, computer scientists have formalized the idea of access control, building
models and mathematically proving different policies. The most versatile and widely used
model is called the access control matrix . Shown in Figure 9.1 , the access control matrix
is comprised of a grid, with resources on one axis and entities that can access those
resources on the other. The entries in the grid represent the rights those entities have over
the corresponding resources. Using this model, we can represent all security situations for
any system. Unfortunately, the sheer number of possibilities makes it very difficult to use
for any practical purposes in its complete form (representing all resources and possible
2
This idea, by the authors ’ admission, had been around since at least 1965.
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