CAP Security Architecture & Engineering 2 — Questions and Answers
Question 1: Which security principle states that a failed security mechanism should deny access rather than allow it?
- Fail-safe defaults (Correct answer)
- Complete mediation
- Open design
- Separation of privilege
Correct answer: Fail-safe defaults
Fail-safe defaults means that when a system or security control fails, it defaults to a secure state — denying access rather than permitting it.
Question 2: What does the security architecture principle of 'complete mediation' require?
- All access requests must pass through a single centralized security gateway
- Every access to every object must be checked against the access control policy each time access is attempted (Correct answer)
- Security controls must be applied at every OSI network layer simultaneously
- All users must complete multi-factor authentication before accessing any resource
Correct answer: Every access to every object must be checked against the access control policy each time access is attempted
Complete mediation requires that every access request to every object is validated against access controls each time, with no caching of previous authorization decisions.
Question 3: In federal security architecture, what is a 'common control' as defined in NIST guidance?
- A security control implemented identically across all information systems in an agency
- A security control whose implementation is managed by an external entity and can be inherited by multiple information systems (Correct answer)
- A mandatory baseline control that every federal system must implement regardless of categorization
- A control shared between the system owner and the user community
Correct answer: A security control whose implementation is managed by an external entity and can be inherited by multiple information systems
Common controls are security controls provided by an organizational entity (e.g., a data center team) and inherited by multiple information systems, reducing duplicated implementation effort.
Question 4: In the Biba Integrity Model, what does the 'simple integrity axiom' (no read down) state?
- A subject cannot read objects at a lower integrity level than its own (Correct answer)
- A subject cannot write to objects at a higher integrity level than its own
- A subject cannot read objects at a higher integrity level than its own
- A subject cannot modify objects at a lower integrity level than its own
Correct answer: A subject cannot read objects at a lower integrity level than its own
The simple integrity axiom prevents a subject from reading data at a lower integrity level, protecting the subject from contamination by less-trusted data.
Question 5: What is the significance of 'security categorization' as the first step of the RMF for security architecture decisions?
- It assigns a dollar value to information assets to prioritize security spending
- It determines the potential impact (Low, Moderate, High) of a breach of confidentiality, integrity, or availability, driving control baseline selection (Correct answer)
- It classifies information as classified or unclassified for mandatory access control purposes
- It ranks systems by the number of users to determine infrastructure scaling requirements
Correct answer: It determines the potential impact (Low, Moderate, High) of a breach of confidentiality, integrity, or availability, driving control baseline selection
Security categorization using FIPS 199 determines the system's impact level, which in turn determines the appropriate baseline of security controls from NIST SP 800-53B.
Question 6: Which security architecture concept describes using role assignments rather than individual user identities to determine access rights?
- Discretionary Access Control (DAC)
- Mandatory Access Control (MAC)
- Role-Based Access Control (RBAC) (Correct answer)
- Attribute-Based Access Control (ABAC)
Correct answer: Role-Based Access Control (RBAC)
RBAC assigns permissions to roles (e.g., 'system administrator') and then assigns users to those roles, simplifying access management in large organizations.
Question 7: What does the principle of 'economy of mechanism' require in secure system design?
- Selecting security products that offer the best value for the acquisition budget
- Keeping security mechanisms as simple and small as possible to reduce the attack surface and ease verification (Correct answer)
- Minimizing the number of security staff required to operate the system
- Reducing operational security costs through automation wherever possible
Correct answer: Keeping security mechanisms as simple and small as possible to reduce the attack surface and ease verification
Economy of mechanism holds that simpler designs are easier to verify, test, and trust — complexity introduces potential for undetected flaws.
CAP Security Architecture & Engineering 2
Which security principle states that a failed security mechanism should deny access rather than allow it?