What is defined as the hardware, firmware and software elements of a trusted computing base that implement
the reference monitor concept?

A.
The reference monitor

B.
Protection rings

C.
A security kernel

D.
A protection domain

Explanation:
A security kernel is defined as the hardware, firmware and software elements of a trusted computing base that
implement the reference monitor concept. A reference monitor is a system component that enforces access
controls on an object. A protection domain consists of the execution and memory space assigned to each
process. The use of protection rings is a scheme that supports multiple protection domains.
KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of
Computer Security, John Wiley & Sons, 2001, Chapter 5: Security Architecture and Models (page 194).