Quick Answer
The answer is AES-256-GCM, as it is the only option that delivers both confidentiality and integrity for data at rest through authenticated encryption. This mode combines AES-256 encryption with Galois/Counter Mode, which produces an authentication tag that verifies the ciphertext has not been altered, ensuring that stored data remains both secret and tamper-proof in a single algorithm. On the CompTIA SecurityX CAS-004 exam, this question tests your ability to distinguish between cryptographic primitives: RSA-2048 provides confidentiality but no built-in integrity, SHA-256 is a hash-only function, and Diffie-Hellman is strictly for key exchange. A common trap is assuming any encryption alone guarantees integrity, but only authenticated encryption modes like GCM or CCM do. Remember the mnemonic “GCM Guards Confidentiality and Message integrity” to recall that GCM wraps both protections into one operation.
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.
A security engineer needs to implement a solution that provides both confidentiality and integrity for data at rest. Which cryptographic method BEST meets these requirements?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
AES-256-GCM
AES-256-GCM provides both encryption and authentication, satisfying confidentiality and integrity requirements.
SHA-256
Why wrong: SHA-256 is a cryptographic hash function that provides integrity but not confidentiality.
Diffie-Hellman
Why wrong: Diffie-Hellman is a key exchange protocol, not used for data at rest.
RSA-2048
Why wrong: RSA is asymmetric encryption; it does not provide data integrity natively.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
AES-256-GCM
AES-256-GCM is an authenticated encryption mode that provides both confidentiality (encryption) and integrity (authentication) in a single algorithm. RSA-2048 is asymmetric and does not provide data integrity directly. SHA-256 is a hash function only. Diffie-Hellman is a key exchange protocol.
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.
AES-256-GCM
Why this is correct
AES-256-GCM provides both encryption and authentication, satisfying confidentiality and integrity requirements.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
SHA-256
Why it's wrong here
SHA-256 is a cryptographic hash function that provides integrity but not confidentiality.
Diffie-Hellman
Why it's wrong here
Diffie-Hellman is a key exchange protocol, not used for data at rest.
RSA-2048
Why it's wrong here
RSA is asymmetric encryption; it does not provide data integrity natively.
Common exam traps
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
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.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
Identify which CAS-004 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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FAQ
Security Engineering — This question tests Security Engineering — Read the scenario before looking for a memorised answer..
The correct answer is: AES-256-GCM — AES-256-GCM is an authenticated encryption mode that provides both confidentiality (encryption) and integrity (authentication) in a single algorithm. RSA-2048 is asymmetric and does not provide data integrity directly. SHA-256 is a hash function only. Diffie-Hellman is a key exchange protocol.
Identify which CAS-004 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.
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This CAS-004 practice question is part of Courseiva's free CompTIA 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 CAS-004 exam.
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