Because the Reference Monitor is responsible for access control to the
objects by the subjects it compares the security labels of a subject and an object.
According to the OIG: The reference monitor is an access control concept referring to an
abstract machine that mediates all accesses to objects by subjects based on information in
an access control database. The reference monitor must mediate all access, be protected
from modification, be verifiable as correct, and must always be invoked. The reference
monitor, in accordance with the security policy, controls the checks that are made in the
access control database.
The following are incorrect:
Validation Module. A Validation Module is typically found in application source code and is
used to validate data being inputted.
Clearance Check. Is a distractor, there is no such thing other than what someone would do
when checking if someone is authorized to access a secure facility.
Security Module. Is typically a general purpose module that prerforms a variety of security
related functions.
References:
OIG CBK, Security Architecture and Design (page 324)
AIO, 4th Edition, Security Architecture and Design, pp 328-328.
Wikipedia - http://en.wikipedia.org/wiki/Reference_monitor