- A
SSE-S3 (Amazon S3-managed keys)
Why wrong: SSE-S3 uses AWS-managed keys — AWS controls the keys and can decrypt data. A customer has no independent control over the encryption keys.
- B
SSE-KMS with an AWS managed CMK (aws/s3)
Why wrong: AWS managed CMKs are controlled by AWS — the customer doesn't have independent control over key rotation, access policies, or deletion.
- C
SSE-KMS with a customer-managed CMK
Customer-managed CMKs give the customer control over key policies, rotation, and deletion. Disabling or deleting the CMK makes the data unreadable — even by AWS. Key usage is auditable via CloudTrail.
- D
S3 Versioning with MFA Delete
Why wrong: MFA Delete protects against unauthorized deletion of object versions — it doesn't encrypt the data or control encryption key ownership.
Quick Answer
The answer is SSE-KMS with a customer-managed CMK. This encryption method is correct because it places the encryption key under your exclusive control, separate from the S3 service itself. Even if an attacker compromises the S3 infrastructure, they cannot decrypt your data without also gaining access to your customer-managed CMK in AWS KMS, which you can further protect with key policies, IAM policies, and rotation. On the AWS Certified Cloud Practitioner CLF-C02 exam, this scenario tests your understanding of the shared responsibility model and the difference between AWS-managed and customer-controlled keys. A common trap is choosing SSE-S3, which uses AWS-managed keys and would not prevent an attacker with S3 access from reading the data. Remember the memory tip: “Customer-managed CMK means customer-controlled access—if S3 is breached, the key is still out of reach.”
CLF-C02 Security and Compliance Practice Question
This CLF-C02 practice question tests your understanding of security and compliance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 company stores sensitive financial data in Amazon S3. They need to ensure that even if an attacker gains access to the S3 service, they cannot read the data without a customer-controlled encryption key. Which S3 encryption method satisfies this requirement?
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
SSE-KMS with a customer-managed CMK
Option C is correct because SSE-KMS with a customer-managed CMK ensures that the encryption key is under the customer's exclusive control, not AWS. Even if an attacker gains access to the S3 service, they cannot decrypt the data without the customer-managed CMK, which is stored in AWS KMS and can be further protected with key policies, IAM policies, and optional key rotation. This satisfies the requirement that the attacker cannot read the data without a customer-controlled encryption key.
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.
- ✗
SSE-S3 (Amazon S3-managed keys)
Why it's wrong here
SSE-S3 uses AWS-managed keys — AWS controls the keys and can decrypt data. A customer has no independent control over the encryption keys.
- ✗
SSE-KMS with an AWS managed CMK (aws/s3)
Why it's wrong here
AWS managed CMKs are controlled by AWS — the customer doesn't have independent control over key rotation, access policies, or deletion.
- ✓
SSE-KMS with a customer-managed CMK
Why this is correct
Customer-managed CMKs give the customer control over key policies, rotation, and deletion. Disabling or deleting the CMK makes the data unreadable — even by AWS. Key usage is auditable via CloudTrail.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
S3 Versioning with MFA Delete
Why it's wrong here
MFA Delete protects against unauthorized deletion of object versions — it doesn't encrypt the data or control encryption key ownership.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'customer-managed' with 'AWS managed' and assume any KMS key provides customer control, but only a customer-managed CMK gives the customer exclusive control over the key's lifecycle and permissions.
Detailed technical explanation
How to think about this question
SSE-KMS with a customer-managed CMK uses envelope encryption: S3 generates a data key from the CMK to encrypt the object, and the encrypted data key is stored alongside the object. The customer can enforce key policies, disable the key, or schedule key deletion, providing a break-glass mechanism. In a real-world scenario, if an attacker compromises an IAM role with S3 read access but lacks KMS Decrypt permission on the customer-managed CMK, they cannot read the encrypted objects, even with full S3 service access.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
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Security and Compliance — study guide chapter
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FAQ
Questions learners often ask
What does this CLF-C02 question test?
Security and Compliance — This question tests Security and Compliance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: SSE-KMS with a customer-managed CMK — Option C is correct because SSE-KMS with a customer-managed CMK ensures that the encryption key is under the customer's exclusive control, not AWS. Even if an attacker gains access to the S3 service, they cannot decrypt the data without the customer-managed CMK, which is stored in AWS KMS and can be further protected with key policies, IAM policies, and optional key rotation. This satisfies the requirement that the attacker cannot read the data without a customer-controlled encryption key.
What should I do if I get this CLF-C02 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.
About these practice questions
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Last reviewed: Jun 11, 2026
This CLF-C02 practice question is part of Courseiva's free Amazon Web Services 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 CLF-C02 exam.
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