The answer is to use an S3 bucket policy that denies PutObject if the x-amz-server-side-encryption-aws-kms-key-id header is not present. This is the most secure way to enforce SSE-KMS encryption on all S3 buckets because bucket policies are evaluated at the request level before the object is written, allowing you to explicitly reject any upload that does not include the required KMS key ID header. In contrast, default encryption settings can be overridden by a client specifying a different encryption header, and IAM policies cannot inspect object-level metadata like encryption headers. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this question tests your understanding of the difference between preventive controls (bucket policies) and detective controls (AWS Config), with the common trap being to choose default encryption or IAM policies. Remember the memory tip: “Deny the header, lock the data” — if the header is missing, the policy denies the PutObject, ensuring every object is encrypted with your specific KMS key.
SAP-C02 Continuous Improvement for Existing Solutions Practice Question
This SAP-C02 practice question tests your understanding of continuous improvement for existing solutions. 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 team requires that all data be encrypted at rest using server-side encryption with a customer-managed key (SSE-KMS). What is the MOST secure way to enforce this requirement across all S3 buckets?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use an S3 bucket policy that denies PutObject if the x-amz-server-side-encryption-aws-kms-key-id header is not present.
Option A is correct because S3 bucket policies can deny PutObject requests that do not specify the required encryption, ensuring SSE-KMS is used. Option B is wrong because S3 default encryption only applies if no encryption header is set, but can be overridden. Option C is wrong because IAM policies can restrict API calls but not enforce encryption on objects. Option D is wrong because AWS Config can detect non-compliant objects but not prevent them.
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 AWS Config rules to detect unencrypted objects and remediate with Lambda.
Why it's wrong here
Reactive, not preventive.
✗
Enable default encryption on each bucket with SSE-KMS.
Why it's wrong here
Can be overridden.
✗
Create an IAM policy that requires kms:Encrypt permission for all S3 operations.
Why it's wrong here
Doesn't enforce on objects.
✓
Use an S3 bucket policy that denies PutObject if the x-amz-server-side-encryption-aws-kms-key-id header is not present.
Why this is correct
Enforces encryption at upload.
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 SAP-C02 ACL questions on filtering logic and placement.
Continuous Improvement for Existing Solutions — This question tests Continuous Improvement for Existing Solutions — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Use an S3 bucket policy that denies PutObject if the x-amz-server-side-encryption-aws-kms-key-id header is not present. — Option A is correct because S3 bucket policies can deny PutObject requests that do not specify the required encryption, ensuring SSE-KMS is used. Option B is wrong because S3 default encryption only applies if no encryption header is set, but can be overridden. Option C is wrong because IAM policies can restrict API calls but not enforce encryption on objects. Option D is wrong because AWS Config can detect non-compliant objects but not prevent them.
What should I do if I get this SAP-C02 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 SAP-C02 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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