Quick Answer
The answer is economy of mechanism, which is one of the core security design principles for CISSP. This principle advocates for keeping the design of a security mechanism as simple and small as possible, because a simpler system has fewer points of failure and is easier to verify and test for vulnerabilities. In contrast, the open design principle, which is also correct in this context, relies on Kerckhoffs’s principle—security should depend on the secrecy of the key, not the algorithm—allowing public scrutiny to strengthen the system. On the Certified Information Systems Professional CISSP exam, these principles test your understanding of foundational design concepts that reduce attack surfaces and enhance trust. A common trap is confusing economy of mechanism with open design, but remember: economy focuses on simplicity, while open design focuses on transparency. A useful memory tip is “Keep it simple, keep it open”—two distinct pillars of secure architecture.
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.
Which THREE of the following are common security design principles? (Select THREE.)
Open design
Correct. Security should not depend on secrecy of design.
Least privilege
Correct. Grant minimum permissions necessary.
Single point of failure
Why wrong: Incorrect. This is an anti-pattern, not a principle.
Security through obscurity
Why wrong: Incorrect. Obscurity is not a reliable security principle.
Economy of mechanism
Correct. Keep the design as simple as possible.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Open design
Open design (A) is a fundamental security principle stating that the security of a system should not depend on the secrecy of its implementation; instead, it relies on the strength of its cryptographic keys and algorithms. This principle is embodied in Kerckhoffs's principle, which asserts that a cryptosystem should remain secure even if everything about the system, except the key, is public knowledge. Open design allows for public scrutiny and peer review, which helps identify vulnerabilities and build trust in the system's security.
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.
Open design
Why this is correct
Correct. Security should not depend on secrecy of design.
Related concept
Read the scenario before looking for a memorised answer.
Least privilege
Why this is correct
Correct. Grant minimum permissions necessary.
Related concept
Read the scenario before looking for a memorised answer.
Single point of failure
Why it's wrong here
Incorrect. This is an anti-pattern, not a principle.
Security through obscurity
Why it's wrong here
Incorrect. Obscurity is not a reliable security principle.
Economy of mechanism
Why this is correct
Correct. Keep the design as simple as possible.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates may confuse 'single point of failure' as a design principle (it is a risk to be mitigated, not a principle) or mistakenly think 'security through obscurity' is a valid principle, when in fact the CISSP explicitly teaches that it is not a reliable security measure.
Detailed technical explanation
The principle of economy of mechanism (E) advocates for simple, small, and well-understood designs to minimize the attack surface and reduce the likelihood of implementation errors. For example, a simple firewall rule set with fewer lines of iptables rules is easier to audit and less prone to misconfiguration than a complex, bloated rule set. Under the hood, simpler code paths reduce the number of conditional branches and state transitions, which directly lowers the probability of exploitable bugs like buffer overflows or race conditions.
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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Architecture and Engineering — study guide chapter
Learn the concepts, then practise the questions
Security Architecture and Engineering practice questions
Targeted practice on this topic area only
All CISSP questions
529 questions across all exam domains
Certified Information Systems Security Professional CISSP study guide
Full concept coverage aligned to exam objectives
CISSP practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise CISSP questions linked to Software Development Security.
Practise CISSP questions linked to Security Assessment and Testing.
Practise CISSP questions linked to Identity and Access Management.
Practise CISSP questions linked to Security and Risk Management.
Practise CISSP questions linked to Security Architecture and Engineering.
Practise CISSP questions linked to Communication and Network Security.
Practise CISSP questions linked to Asset Security.
Practise CISSP questions linked to Security Operations.
Practise CISSP questions linked to CISSP fundamentals.
Practise CISSP questions linked to CISSP scenario.
Practise CISSP questions linked to CISSP troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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: Open design — Open design (A) is a fundamental security principle stating that the security of a system should not depend on the secrecy of its implementation; instead, it relies on the strength of its cryptographic keys and algorithms. This principle is embodied in Kerckhoffs's principle, which asserts that a cryptosystem should remain secure even if everything about the system, except the key, is public knowledge. Open design allows for public scrutiny and peer review, which helps identify vulnerabilities and build trust in the system's security.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which THREE are core principles of secure system design?
easyWhy C: The principle of least privilege mandates that users, processes, or systems should be granted only the minimum permissions necessary to perform their function. This reduces the attack surface and limits potential damage from compromised accounts or software flaws. In secure system design, it is enforced through access control lists (ACLs), role-based access control (RBAC), and mandatory access control (MAC) models.
Last reviewed: Jun 24, 2026
This CISSP practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CISSP exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.