The correct answer is to use S3 Batch Operations with a Lambda function to apply SSE-KMS encryption to all existing objects using the required KMS key. This is because S3 Batch Operations can process millions of objects across a bucket, invoking a Lambda function that performs a copy-in-place operation to rewrite each object with the desired server-side encryption settings, effectively encrypting existing objects that were uploaded before default encryption was enabled. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of how to remediate encryption compliance gaps at scale without disrupting ongoing access—a common trap is assuming a bucket policy or default encryption retroactively fixes old objects, but those only apply to new uploads. A key memory tip is: "Batch and Lambda fix the past; policies and defaults guard the future."
DEA-C01 Data Security and Governance Practice Question
This DEA-C01 practice question tests your understanding of data security and governance. 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 sensitive customer data. The security policy requires that all objects in the bucket be encrypted at rest using server-side encryption with a customer-managed KMS key. The data engineer has enabled default encryption on the bucket using SSE-KMS with the required KMS key. However, a security scan reveals that some objects in the bucket are not encrypted with the KMS key. The objects were uploaded before the default encryption was enabled. The data engineer needs to ensure that all objects are encrypted with the KMS key without disrupting ongoing data access. What should the data engineer do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use S3 Batch Operations with a Lambda function to apply SSE-KMS encryption to all existing objects using the KMS key.
Option A is correct. S3 Batch Operations can apply SSE-KMS encryption to existing objects using the KMS key. Option B is wrong because copying objects manually is inefficient and error-prone. Option C is wrong because the bucket policy only prevents new unencrypted uploads. Option D is wrong because deleting and re-uploading is disruptive.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Use the AWS CLI to copy the objects to themselves with the --sse-kms-key-id parameter.
Why it's wrong here
Manual and not scalable.
✗
Modify the bucket policy to deny access to objects not encrypted with the KMS key.
Why it's wrong here
This does not encrypt existing objects, it denies access.
✗
Delete the unencrypted objects and re-upload them with encryption.
Why it's wrong here
Disruptive and risks data loss.
✓
Use S3 Batch Operations with a Lambda function to apply SSE-KMS encryption to all existing objects using the KMS key.
Why this is correct
S3 Batch Operations can encrypt existing objects in place.
Related concept
Standard ACLs match source addresses.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DEA-C01 ACL questions on filtering logic and placement.
Data Security and Governance — This question tests Data Security and Governance — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Use S3 Batch Operations with a Lambda function to apply SSE-KMS encryption to all existing objects using the KMS key. — Option A is correct. S3 Batch Operations can apply SSE-KMS encryption to existing objects using the KMS key. Option B is wrong because copying objects manually is inefficient and error-prone. Option C is wrong because the bucket policy only prevents new unencrypted uploads. Option D is wrong because deleting and re-uploading is disruptive.
What should I do if I get this DEA-C01 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DEA-C01 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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