This CISSP practice question tests your understanding of security architecture and engineering. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A security engineer is reviewing the architecture of a system that uses the Bell-LaPadula model. The system has subjects with security clearances and objects with classifications. To prevent covert timing channels, which additional control should be implemented?
Enforce strict data labeling
Why wrong: Data labeling is already part of BLP; it does not address timing channels.
Implement audit logging
Why wrong: Audit logging detects but does not prevent timing channels.
Disable concurrent access to shared resources
Correct. Limiting concurrency reduces timing channel opportunities.
Use encryption for data at rest
Why wrong: Encryption protects confidentiality but not timing channels.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Disable concurrent access to shared resources
Covert timing channels exploit the ability of a subject to modulate the timing of its access to a shared resource, thereby leaking information to another subject at a different security level. The Bell-LaPadula model enforces mandatory access control (MAC) but does not inherently prevent these channels. Disabling concurrent access to shared resources (option C) eliminates the ability to use timing variations as a signaling mechanism, directly addressing the covert channel at the resource scheduling level.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Enforce strict data labeling
Why it's wrong here
Data labeling is already part of BLP; it does not address timing channels.
Implement audit logging
Why it's wrong here
Audit logging detects but does not prevent timing channels.
Disable concurrent access to shared resources
Why this is correct
Correct. Limiting concurrency reduces timing channel opportunities.
Related concept
Read the scenario before looking for a memorised answer.
Use encryption for data at rest
Why it's wrong here
Encryption protects confidentiality but not timing channels.
Common exam traps
The trap here is that candidates confuse covert timing channels with covert storage channels (which involve writing data to a shared attribute) and incorrectly choose audit logging or encryption as a catch-all solution, rather than recognizing that timing channels require controlling the concurrency of resource access.
Detailed technical explanation
A covert timing channel works by having a high-level subject alter the timing of its resource usage (e.g., disk I/O, CPU cycles) in a pattern that a low-level subject can observe and decode into bits. The Bell-LaPadula model's focus on read-up/write-down restrictions does not constrain the order or duration of resource accesses. Disabling concurrent access—for example, by serializing access to a shared disk or using a single-threaded scheduler—removes the observable timing variance, effectively closing the channel. In practice, this is often achieved through resource partitioning or using a reference monitor that enforces non-interference properties.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
What to study next
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FAQ
Security Architecture and Engineering — This question tests Security Architecture and Engineering — Read the scenario before looking for a memorised answer..
The correct answer is: Disable concurrent access to shared resources — Covert timing channels exploit the ability of a subject to modulate the timing of its access to a shared resource, thereby leaking information to another subject at a different security level. The Bell-LaPadula model enforces mandatory access control (MAC) but does not inherently prevent these channels. Disabling concurrent access to shared resources (option C) eliminates the ability to use timing variations as a signaling mechanism, directly addressing the covert channel at the resource scheduling level.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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