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elonging to a decision subsystem or an enforcement subsystem. The five
interrelated security subsystems proposed here and depicted in Figure 2-4 on
page 63, expand the operating system-based concept and suggest that function
and interdependency of security-related functions, beyond centralized access
control, can be modeled as well.
Figure 2-4 IT Security processes and subsystems
A brief description of each of the five security subsystems, along with further
detail of the aggregation of CC component-level criteria within each subsystem,
is now provided. The subsystem diagrams are represented as parts of a
closed-loop control system showing the internal processes that each performs,
along with its external interfaces. In this representation, each subsystem consists
of a managing process with a default idle state and several execution paths that
can be invoked either by an asynchronous request signaled by another security
subsystem or by a synchronized request from a non-security process.
Complementary representations composed of component views and interaction
diagrams for the subsystems are being developed.
Chapter 2. Security methodologies 63