The answer is to use well-vetted, standard cryptographic algorithms and generate cryptographic keys using a cryptographically secure random number generator. These two principles are foundational because standard algorithms like AES, RSA, and ECDSA have survived years of public cryptanalysis, ensuring their security properties are proven and reliable, while a cryptographically secure random number generator prevents predictable key generation that attackers could exploit. On the CompTIA SecurityX CAS-004 exam, this topic tests your understanding of cryptographic design principles and the dangers of proprietary or custom algorithms, which often harbor hidden vulnerabilities. A common trap is assuming any random number generator suffices—remember that only a CSPRNG meets the entropy requirements for secure keys. Memory tip: “Standard algorithms, secure seeds” to recall both the algorithm choice and key generation as inseparable design principles.
CAS-004 Security Engineering Practice Question
This CAS-004 practice question tests your understanding of security 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 TWO of the following are considered secure design principles for cryptographic systems?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use well-vetted, standard cryptographic algorithms
Option C is correct because using well-vetted, standard cryptographic algorithms (e.g., AES, RSA, ECDSA) ensures the system benefits from years of public scrutiny, rigorous cryptanalysis, and proven security properties. Proprietary or custom algorithms often contain undiscovered vulnerabilities, making them unsuitable for secure systems.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Implement custom encryption algorithms designed in-house
Why it's wrong here
Custom algorithms are prone to flaws.
✗
Use the same key for encryption and authentication to reduce complexity
Why it's wrong here
Key separation is important; reusing keys can lead to vulnerabilities.
✓
Use well-vetted, standard cryptographic algorithms
Why this is correct
Standard algorithms have been analyzed for weaknesses.
Related concept
Read the scenario before looking for a memorised answer.
✗
Rely on secrecy of the algorithm for security
Why it's wrong here
Security should not depend on algorithm secrecy (Kerckhoffs's principle).
✓
Generate cryptographic keys using a cryptographically secure random number generator
Why this is correct
Weak randomness can lead to predictable keys.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the misconception that 'custom algorithms' or 'security through obscurity' can be acceptable in secure design, when in fact they are explicitly rejected in favor of open, peer-reviewed standards and key separation.
Detailed technical explanation
How to think about this question
Standard algorithms like AES-GCM or ChaCha20-Poly1305 provide authenticated encryption, combining confidentiality and integrity with separate keys or nonces to prevent misuse. In practice, protocols such as TLS 1.3 mandate the use of well-vetted ciphersuites and cryptographically secure random number generators (CSPRNGs) for key generation, as specified in NIST SP 800-90A, to ensure keys are unpredictable and resistant to brute-force attacks.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the CAS-004 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Engineering — This question tests Security Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use well-vetted, standard cryptographic algorithms — Option C is correct because using well-vetted, standard cryptographic algorithms (e.g., AES, RSA, ECDSA) ensures the system benefits from years of public scrutiny, rigorous cryptanalysis, and proven security properties. Proprietary or custom algorithms often contain undiscovered vulnerabilities, making them unsuitable for secure systems.
What should I do if I get this CAS-004 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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