- A
RC4
Why wrong: RC4 is a stream cipher, not a block cipher, and is considered weak.
- B
RSA
Why wrong: RSA is asymmetric, not suitable for bulk data encryption.
- C
AES
Correct. AES meets all requirements.
- D
3DES
Why wrong: 3DES is less secure and slower; NIST has deprecated it.
Question 145 of 1,000
CISSP Security Architecture and Engineering Practice Question
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 architect is selecting a cryptographic algorithm for encrypting data at rest in a backup system. The system requires strong security with a block cipher, and the organization mandates using a NIST-approved algorithm with key sizes of 128, 192, or 256 bits. Which algorithm should be selected?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
AES
AES is a NIST-approved symmetric block cipher supporting 128, 192, and 256-bit keys. It is the standard for data at rest encryption.
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.
- ✗
RC4
Why it's wrong here
RC4 is a stream cipher, not a block cipher, and is considered weak.
- ✗
RSA
Why it's wrong here
RSA is asymmetric, not suitable for bulk data encryption.
- ✓
AES
Why this is correct
Correct. AES meets all requirements.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
3DES
Why it's wrong here
3DES is less secure and slower; NIST has deprecated it.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 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.
Quick reference
Symmetric Encryption Algorithm Comparison
| Algorithm | Key Size | Block Size | Status | Notes |
|---|---|---|---|---|
| AES-128 | 128-bit | 128-bit | Current standard | NIST approved; WPA3, TLS |
| AES-256 | 256-bit | 128-bit | Current standard | Preferred for sensitive / govt data |
| 3DES | 112-bit effective | 64-bit | Deprecated (2023) | Replaced by AES |
| DES | 56-bit | 64-bit | Broken | Cracked in < 24 h; never deploy |
| ChaCha20 | 256-bit | Stream cipher | Current | TLS 1.3, WireGuard |
What to study next
Got this wrong? Here's your next step.
Identify which CISSP exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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Security Architecture and Engineering — study guide chapter
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FAQ
Questions learners often ask
What does this CISSP question test?
Security Architecture and Engineering — This question tests Security Architecture and Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: AES — AES is a NIST-approved symmetric block cipher supporting 128, 192, and 256-bit keys. It is the standard for data at rest encryption.
What should I do if I get this CISSP question wrong?
Identify which CISSP exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 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.
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