Information Technology Reference
In-Depth Information
status. For example, usage of certain digital resources may be allowed only during
business hours or at certain locations. A system with heavy trac load may allow
only premium users to be serviced. For this requirement, a system needs to check
current environmental or system status for usage decision. This decision factor
is called as “condition” and required together with authorization and obligation
for modern access control.
pre
ongoing
Continuity of
Decisions
Before
Usage
After
Mutability of
Attributes
pre
ongoing
post
Fig. 2.
Continuity and Mutability Properties
In addition to these three decision factors, modern information systems re-
quire two other important properties called
“continuity”
and
“mutability”
as
shown in Figure 2. In traditional access control, authorization is assumed to be
done before access is allowed (pre). However, it is quite reasonable to extend this
for continuous enforcement by evaluating usage requirements throughout usages
(ongoing). This property is called “continuity” and has to be captured in mod-
ern access control for the control of relatively long-lived usage or for immediate
revocation of usage.
In traditional access control, attributes are modifiable only by administrative
actions. However, in many modern applications such as DRM systems, these
attributes have to be updated as side-effects of subjects' actions. For example, a
subject's e-cash balance has to be decreased by the value of a digital object as the
subject uses or accesses the object. This “mutability” property of attributes has
been rarely discussed in traditional access control literature. In case attributes
are mutable, updates can be done either before (pre), during (ongoing) or after
(post) usages as shown in Figure 2. Mutability allows more direct enforcement
of various classical policies that require history-based authorizations such as
dynamic Separation Of Duty or Chinese Wall policy.
Although some of these issues have been discussed in access control literature,
the focus is typically limited to specific target problems, so the discussion is not
comprehensive. The notion of usage control (UCON) is developed to cover these
diverse issues in a single framework to overcome these shortcomings. In UCON,
traditional access control can be extended to include modern access control and
digital rights management by integrating obligations and conditions as well as
authorizations and by including continuity and mutability properties.
