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The security perimeter is the imaginary line that separates the trusted components of the kernel and the Trusted Computing Base (TCB) from those elements that are not trusted. The reference monitor is an abstract machine that mediates all accesses to objects by subjects. The security kernel can be software, firmware or hardware components in a trusted system and is the actual instantiation of the reference monitor. The reference perimeter is not defined and is a distracter.

Source: HARE, Chris, Security Architecture and Models, Area 6 CISSP Open Study Guide, January 2002.

The Orange book requires protection against two types of covert channels, Timing and Storage.

The following answers are incorrect:

Storage and low bits. Is incorrect because, low bits would not be considered a covert channel.

Storage and permissions. Is incorrect because, permissions would not be considered a covert channel.

Storage and classification. Is incorrect because, classification would not be considered a covert channel.

A security kernel is responsible for enforcing a security policy. It is a strict implementation of a reference monitor mechanism. The architecture of a kernel operating system is typically layered, and the kernel should be at the lowest and most primitive level.

It is a small portion of the operating system through which all references to information and all changes to authorizations must pass. In theory, the kernel implements access control and information flow control between implemented objects according to the security policy.

To be secure, the kernel must meet three basic conditions:

completeness (all accesses to information must go through the kernel),

isolation (the kernel itself must be protected from any type of unauthorized access),

and verifiability (the kernel must be proven to meet design specifications).

The reference monitor, as noted previously, is an abstraction, but there may be a reference validator, which usually runs inside the security kernel and is responsible for performing security access checks on objects, manipulating privileges, and generating any resulting security audit messages.

A term associated with security kernels and the reference monitor is the trusted computing base (TCB). The TCB is the portion of a computer system that contains all elements of the system responsible for supporting the security policy and the isolation of objects. The security capabilities of products for use in the TCB can be verified through various evaluation criteria, such as the earlier Trusted Computer System Evaluation Criteria (TCSEC) and the current Common Criteria standard.

Many of these security terms—reference monitor, security kernel, TCB—are defined loosely by vendors for purposes of marketing literature. Thus, it is necessary for security professionals to read the small print and between the lines to fully understand what the vendor is offering in regard to security features.

TIP FOR THE EXAM:

The terms Security Kernel and Reference monitor are synonymous but at different levels.

As it was explained by Diego:

While the Reference monitor is the concept, the Security kernel is the implementation of such concept (via hardware, software and firmware means).

The two terms are the same thing, but on different levels: one is conceptual, one is "technical"

The following are incorrect answers:

Confidentiality, Integrity, and Availability

Policy, mechanism, and assurance

Isolation, layering, and abstraction

Reference(s) used for this question:

Hernandez CISSP, Steven (2012-12-21). Official (ISC)2 Guide to the CISSP CBK, Third Edition ((ISC)2 Press) (Kindle Locations 13858-13875). Auerbach Publications. Kindle Edition.

It is considered to be a technical control.

Logical is synonymous with Technical Control. That was the easy answer.

There are three broad categories of access control: Administrative, Technical, and Physical.

Each category has different access control mechanisms that can be carried out manually or automatically. All of these access control mechanisms should work in concert with each other to protect an infrastructure and its data.

Each category of access control has several components that fall within it, as shown here:

Administrative Controls

• Policy and procedures

• Personnel controls

• Supervisory structure

• Security-awareness training

• Testing

Physical Controls

Network segregation

Perimeter security

Computer controls

Work area separation

Data backups

Technical Controls

System access

Network architecture

Network access

Encryption and protocols

Control zone

Auditing

The following answers are incorrect :

Screening of personnel is considered to be an administrative control

Development of policies, standards, procedures and guidelines is considered to be an administrative control

Change control procedures is considered to be an administrative control.

Reference : Shon Harris AIO v3 , Chapter - 3 : Security Management Practices , Page : 52-54