The answer is a mismatch between the SSE-S3 requirement in the IAM policy and the SSE-KMS encryption specified in the CLI command. The IAM policy explicitly conditions the `s3:PutObject` action on the `s3:x-amz-server-side-encryption` header being set to `AES256`, which enforces SSE-S3. When you use `--sse aws:kms` in the AWS CLI, that header is set to `aws:kms` instead, failing the policy’s condition check and triggering the AccessDenied error. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of how IAM policy conditions enforce specific encryption types at the object level, a common trap where candidates overlook that the header value must exactly match the policy’s requirement. The key distinction is that SSE-S3 uses `AES256` while SSE-KMS uses `aws:kms`, and the policy acts as a gatekeeper for that header. Memory tip: think “AES for S3, KMS for key” — the header value tells you which encryption service is being demanded.
DEA-C01 Data Store Management Practice Question
This DEA-C01 practice question tests your understanding of data store management. 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 data engineer created the IAM policy shown in the exhibit. The engineer then attempts to upload an object to 'my-bucket' using the AWS CLI with the command: aws s3 cp file.txt s3://my-bucket/ --sse aws:kms. The upload fails with an 'AccessDenied' error. What is the most likely cause?
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 policy requires SSE-S3 (AES256), but the command uses SSE-KMS
The IAM policy in the exhibit requires the `s3:x-amz-server-side-encryption` header to be set to `AES256`, which corresponds to SSE-S3. The AWS CLI command uses `--sse aws:kms`, which sets the header to `aws:kms` for SSE-KMS. This mismatch causes the request to fail the `s3:PutObject` condition check in the policy, resulting in an 'AccessDenied' error.
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 policy resource is incorrect
Why it's wrong here
The resource is correct for the bucket.
✓
The policy requires SSE-S3 (AES256), but the command uses SSE-KMS
Why this is correct
The condition mandates AES256, but the command uses aws:kms.
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 policy does not allow the s3:PutObject action
Why it's wrong here
The policy allows s3:PutObject.
✗
The command is missing the --sse-customer-algorithm parameter
Why it's wrong here
The command includes --sse, but the encryption type does not match.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may overlook the condition key in the policy and assume the error is due to a missing action or incorrect resource, rather than recognizing that the encryption header value must exactly match the policy's requirement.
Trap categories for this question
Command / output trap
The command includes --sse, but the encryption type does not match.
Detailed technical explanation
How to think about this question
The condition key `s3:x-amz-server-side-encryption` in the policy enforces a specific encryption header value at the HTTP request level. When using the AWS CLI with `--sse aws:kms`, the SDK automatically sets the `x-amz-server-side-encryption` header to `aws:kms`. If the policy only allows `AES256`, any request with a different encryption header value (or without the header) will be denied. This is a common pattern to enforce encryption standards across an organization, ensuring all objects uploaded use a specific encryption type.
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.
Data Store Management — This question tests Data Store Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The policy requires SSE-S3 (AES256), but the command uses SSE-KMS — The IAM policy in the exhibit requires the `s3:x-amz-server-side-encryption` header to be set to `AES256`, which corresponds to SSE-S3. The AWS CLI command uses `--sse aws:kms`, which sets the header to `aws:kms` for SSE-KMS. This mismatch causes the request to fail the `s3:PutObject` condition check in the policy, resulting in an 'AccessDenied' error.
What should I do if I get this DEA-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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