Chapter 11 (Lecture 10)

Question 1

1. Name at least seven security models.

Answer 1

1. Security models include 
state machine, 
information flow, 
noninterference, 
Take-Grant,
 access control matrix,
 Bell-LaPadula, 
Biba, 
Clark-Wilson, 
Brewer and Nash (aka Chinese Wall), 
Goguen-Meseguer, 
Sutherland, 
and Graham-Denning.

Question 2

2. Describe the primary components of TCB.

Answer 2

2. The primary components of the trusted computing base (TCB) are the

hardware and software elements used to enforce the security policy (these elements are called the TCB), the

security perimeter distinguishing and separating TCB components from non-TCB components, and

the reference monitor that serves as an access control device across the security perimeter.

Question 3

3. What are the two primary rules or principles of the Bell-LaPadula security model? Also, what are the two rules of Biba?

Answer 3

3. The two primary rules of Bell-LaPadula are the simple rule of no read up and the star rule of no write down. The two rules of Biba are the simple rule of no read down and the star rule of no write up.

Question 4

4. What is the difference between open and closed systems and open and closed source?

Answer 4

4. An open system is one with published APIs that allow third parties to develop products to interact with it. A closed system is one that is proprietary with no third-party product support. Open source is a coding stance that allows others to view the source code of a program. Closed source is an opposing coding stance that keeps source code confidential.

Question 5

1. What is system certification?

A. Formal acceptance of a stated system configuration

B. A technical evaluation of each part of a computer system to assess its compliance with security standards

C. A functional evaluation of the manufacturer’s goals for each hardware and software component to meet integration standards

D. A manufacturer’s certificate stating that all components were installed and configured correctly

Answer 5

1. B. A system certification is a technical evaluation. Option A describes system accreditation. Options C and D refer to manufacturer standards, not implementation standards.

Question 6

2. What is system accreditation?

A. Formal acceptance of a stated system configuration

B. A functional evaluation of the manufacturer’s goals for each hardware and software component to meet integration standards

C. Acceptance of test results that prove the computer system enforces the security policy

D. The process to specify secure communication between machines

Answer 6

2. A. Accreditation is the formal acceptance process. Option B is not an appropriate answer because it addresses manufacturer standards. Options C and D are incorrect because there is no way to prove that a configuration enforces a security policy and accreditation does not entail secure communication specification.

Question 7

3. What is a closed system?

A. A system designed around final, or closed, standards

B. A system that includes industry standards

C. A proprietary system that uses unpublished protocols

D. Any machine that does not run Windows

Answer 7

3. C. A closed system is one that uses largely proprietary or unpublished protocols and standards. Options A and D do not describe any particular systems, and Option B describes an open system.

Question 8

4. Which best describes a confined or constrained process?

A. A process that can run only for a limited time

B. A process that can run only during certain times of the day

C. A process that can access only certain memory locations

D. A process that controls access to an object

Answer 8

4. C. A constrained process is one that can access only certain memory locations. Options A, B, and D do not describe a constrained process.

Question 9

5. What is an access object?

A. A resource a user or process wants to access

B. A user or process that wants to access a resource

C. A list of valid access rules

D. The sequence of valid access types

Answer 9

5. A. An object is a resource a user or process want to access. Option A describes an access object.

Question 10

6. What is a security control?

A. A security component that stores attributes that describe an object

B. A document that lists all data classification types

C. A list of valid access rules

D. A mechanism that limits access to an object

Answer 10

6. D. A control limits access to an object to protect it from misuse by unauthorized users.

Question 11

7. For what type of information system security accreditation are the applications and systems at a specific, self-contained location evaluated?

A. System accreditation

B. Site accreditation

C. Application accreditation

D. Type accreditation

Answer 11

7. B. The applications and systems at a specific, self-contained location are evaluated for DITSCAP and NIACAP site accreditation.

Question 12

8. How many major categories do the TCSEC criteria define?

A. Two

B. Three

C. Four

D. Five

Answer 12

8. C. TCSEC defines four major categories: category A is verified protection, category B is mandatory protection, category C is discretionary protection, and category D is minimal protection.

Question 13

9. What is a trusted computing base (TCB)?

A. Hosts on your network that support secure transmissions

B. The operating system kernel and device drivers

C. The combination of hardware, software, and controls that work together to enforce a security policy

D. The software and controls that certify a security policy

Answer 13

9. C. The TCB is the combination of hardware, software, and controls that work together to enforce a security policy.

Question 14

10. What is a security perimeter? (Choose all that apply.)

A. The boundary of the physically secure area surrounding your system

B. The imaginary boundary that separates the TCB from the rest of the system

C. The network where your firewall resides

D. Any connections to your computer system

Answer 14

10. A, B. Although the most correct answer in the context of this chapter is option B, option A is also a correct answer in the context of physical security.

Question 15

11. What part of the TCB concept validates access to every resource prior to granting the requested access?

A. TCB partition

B. Trusted library

C. Reference monitor

D. Security kernel

Answer 15

11. C. The reference monitor validates access to every resource prior to granting the requested access. Option D, the security kernel, is the collection of TCB components that work together to implement the reference monitor functions. In other words, the security kernel is the implementation of the reference monitor concept. Options A and B are not valid TCB concept components.

Question 16

12. What is the best definition of a security model?

A. A security model states policies an organization must follow.

B. A security model provides a framework to implement a security policy.

C. A security model is a technical evaluation of each part of a computer system to assess its concordance with security standards.

D. A security model is the process of formal acceptance of a certified configuration.

Answer 16

12. B. Option B is the only option that correctly defines a security model. Options A, C, and D define part of a security policy and the certification and accreditation process.

Question 17

13. Which security models are built on a state machine model?

A. Bell-LaPadula and Take-Grant

B. Biba and Clark-Wilson

C. Clark-Wilson and Bell-LaPadula

D. Bell-LaPadula and Biba

Answer 17

13. D. The Bell-LaPadula and Biba models are built on the state machine model.

Question 18

14. Which security model addresses data confidentiality?

A. Bell-LaPadula

B. Biba

C. Clark-Wilson

D. Brewer and Nash

Answer 18

14. A. Only the Bell-LaPadula model addresses data confidentiality. The Biba and Clark-Wilson models address data integrity. The Brewer and Nash model prevents conflicts of interest.

Question 19

15. Which Bell-LaPadula property keeps lower-level subjects from accessing objects with a higher security level?

A. * (star) Security Property

B. No write up property

C. No read up property

D. No read down property

Answer 19

15. C. The no read up property, also called the Simple Security Policy, prohibits subjects from reading a higher security level object.

Question 20

16. What is the implied meaning of the simple property of Biba?

A. Write down

B. Read up

C. No write up

D. No read down

Answer 20

16. B. The simple property of Biba is no read down, but it implies that it is acceptable to read up.

Question 21

17. When a trusted subject violates the star property of Bell-LaPadula in order to write an object into a lower level, what valid operation could be taking place?

A. Perturbation

B. Polyinstantiation

C. Aggregation

D. Declassification

Answer 21

17. D. Declassification is the process of moving an object into a lower level of classification once it is determined that it no longer justifies being placed at a higher level. Only a trusted subject can perform declassification because this action is a violation of the verbiage of the star property of Bell-LaPadula, but not the spirit or intent, which is to prevent unauthorized disclosure.

Question 22

18. What security method, mechanism, or model reveals a capabilities list of a subject across multiple objects?

A. Separation of duties

B. Access control matrix

C. Biba

D. Clark-Wilson

Answer 22

18. B. An access control matrix assembles ACLs from multiple objects into a single table. The rows of that table are the ACEs of a subject across those objects, thus a capabilities list.

Question 23

19. What security model has a feature that in theory has one name or label, but when implemented into a solution, takes on the name or label of the security kernel?

A. Graham-Denning model

B. Deployment modes

C. Trusted computing base

D. Chinese Wall

Answer 23

19. C. The trusted computing base (TCB) has a component known as the reference monitor in theory, which becomes the security kernel in implementation.

Question 24

20. Which of the following is not part of the access triple of the Clark-Wilson model?

A. Object

B. Interface

C. Programming language

D. Subject

Answer 24

20. C. The three parts of the Clark-Wilson model access triple are subject, object, and program (or interface).