The answer is that the user's IAM policy does not include kms:Decrypt permission. While the key policy allows kms:Decrypt, AWS evaluates both the key policy and the user's IAM policy for KMS actions; if the IAM policy is silent or denies the action, the request fails even if the key policy grants it. This is a common trap on the AWS Certified Data Engineer Associate DEA-C01 exam, where candidates assume a key policy alone suffices for SSE-KMS decryption, but IAM policies must explicitly allow kms:Decrypt for the user. The scenario tests your understanding of the layered permission model: S3 bucket policies control object access, KMS key policies control key usage, and IAM policies govern the user’s identity—all three must align. A useful memory tip is “IAM is the gatekeeper for the user; the key policy is the gatekeeper for the key—both gates must open.”
DEA-C01 Data Operations and Support Practice Question
This DEA-C01 practice question tests your understanding of data operations and support. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 uses Amazon S3 to store log files from multiple applications. The logs are encrypted with AWS KMS (SSE-KMS). A data engineer needs to grant a new IAM user read-only access to the logs. The engineer attaches an S3 bucket policy that allows s3:GetObject and a KMS key policy that allows kms:Decrypt. However, the user still receives an 'Access Denied' error when trying to download an object. What is the MOST likely missing permission?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The user's IAM policy does not include kms:Decrypt permission.
Option C is correct because to use SSE-KMS, the user needs kms:Decrypt, but also the IAM policy must allow kms:Decrypt, not just the key policy. The key policy alone is not sufficient if the IAM user's policy denies or does not allow the action. Option A is incorrect because s3:ListBucket is for listing, not downloading. Option B is incorrect because s3:GetObjectVersion is for versioned buckets. Option D is incorrect because kms:GenerateDataKey is for encryption, not decryption.
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.
✗
The user does not have s3:ListBucket permission on the bucket.
Why it's wrong here
ListBucket is for listing objects, not for downloading.
✗
The user does not have s3:GetObjectVersion permission.
Why it's wrong here
If the bucket is not versioned, this permission is not needed.
✓
The user's IAM policy does not include kms:Decrypt permission.
Why this is correct
Both the key policy and the IAM user policy must allow kms:Decrypt; the IAM policy is missing this action.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The user does not have kms:GenerateDataKey permission.
Why it's wrong here
GenerateDataKey is used for encryption, not decryption.
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 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 DEA-C01 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.
Data Operations and Support — This question tests Data Operations and Support — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The user's IAM policy does not include kms:Decrypt permission. — Option C is correct because to use SSE-KMS, the user needs kms:Decrypt, but also the IAM policy must allow kms:Decrypt, not just the key policy. The key policy alone is not sufficient if the IAM user's policy denies or does not allow the action. Option A is incorrect because s3:ListBucket is for listing, not downloading. Option B is incorrect because s3:GetObjectVersion is for versioned buckets. Option D is incorrect because kms:GenerateDataKey is for encryption, not decryption.
What should I do if I get this DEA-C01 question wrong?
Identify which DEA-C01 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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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