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7.1.2.3 Accountability
Accountability is perhaps one of the most important aspects of a strong access control system, but
it is, unfortunately, one of the least implemented facets of access control. Accountability aims at
utilizing methods such as audit trails and logs to associate users of the systems with actions they
perform on the system, to ensure that users are accountable for their actions performed on the
system. For instance, if the administrator of a system continuously creates dummy user IDs and
steals sensitive information from the system, then there would be no way of tracing the incidents
to the administrator without the presence of an active logging mechanism or audit trail. Audit
trails are aimed at maintaining a certain level of accountability for user actions in the system. We
will discuss audit trails and logging in detail in Chapter 9.
7.1.3 Access Control Models
Access control models are frameworks that deine how a user gains access to system resources.
hese models use the concepts of access control—namely, authentication, authorization, and
accountability—to deine parameters for user access to resources and to also enforce these deini-
tions. here are several models of access controls that are in existence, but we will discuss three of
the most popular models of access control:
◾
Mandatory access control
Discretionary access control
◾
◾
Role-based access control
7.1.3.1 Discretionary Access Control
Discretionary access control, popularly known as DAC, works on the concept of
ownership
. If a user
creates a ile, he is the owner of the ile and is known as the data owner. he data owner dictates who
can or cannot gain access to the ile and what rights users have for the ile created by the data owner. For
instance, Bob creates a ile employees.xls. He might want Scott to be able to read that ile; therefore, he
can specify that he will provide access to Scott to read the ile but do nothing else. Scott cannot edit or
delete the ile created by Bob. In this situation, Bob is the data owner and Scott is the user who Bob has
authorized to view Bob's ile. Discretionary access control mechanisms are enforced through
ACLs
or
Access Control Lists
. hese lists contain the rules for access to a particular ile or resource. hey expressly
contain the subjects (users) that are allowed access to the object (resource) and the privileges of the access
that a subject has to the object. Discretionary access control is used by operating systems like Windows
and Unix-based operating systems to grant/revoke permissions for folders, iles, and applications.
he limitation with discretionary access control has to do with scale and implementation. he
access control model would be very tedious to implement in a large enterprise scenario, where there
are likely to be hundreds of iles, folders, and resources for which access has to be conigured. From
a Web application standpoint as well, DAC is complex as the rights and privileges are deined per
individual and not an individual role, which might lead to a very large number of access control
rules written for each ile/folder/resource.
7.1.3.2 Mandatory Access Control
Mandatory access control, also known as MAC is an access control model that relies on the tenet
of
limiting information dissemination
. MAC is utilized by defense and military organizations and
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