The correct answer is a bucket policy with a condition that denies s3:PutObject unless the request includes the x-amz-server-side-encryption-aws:kms header. This works because the policy uses an explicit Deny effect with the s3:x-amz-server-side-encryption-aws:kms condition key, which blocks any upload that does not specify AWS KMS encryption using a customer managed key. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of how to enforce encryption at rest through IAM policy conditions rather than relying on default bucket settings or client-side checks. A common trap is confusing the s3:x-amz-server-side-encryption condition (which covers AES-256) with the aws:kms variant, or thinking that enabling default encryption on the bucket is sufficient—it is not, because a user can override it with an explicit header. Remember the memory tip: “Deny without KMS, or the upload gets dismissed.”
SCS-C02 Data Protection Practice Question
This SCS-C02 practice question tests your understanding of data protection. 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 is migrating sensitive data to Amazon S3. They need to ensure that data is encrypted at rest using an AWS KMS customer managed key (CMK). The security team wants to enforce encryption for all new objects uploaded to an S3 bucket. Which policy should be attached to the bucket?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A bucket policy with a condition that denies s3:PutObject unless the request includes the x-amz-server-side-encryption-aws:kms header
Option A uses a condition to deny PutObject if encryption is not set, which enforces encryption. Option B only audits, C is too permissive, D allows unencrypted uploads.
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.
✗
A bucket policy that allows s3:PutObject only if the user has KMS permissions
Why it's wrong here
Does not enforce encryption header.
✗
An S3 bucket default encryption setting with AES256
Why it's wrong here
Default encryption can be overridden; does not enforce KMS.
✗
An S3 Lifecycle policy to transition objects to Glacier after 30 days
Why it's wrong here
Lifecycle does not enforce encryption.
✓
A bucket policy with a condition that denies s3:PutObject unless the request includes the x-amz-server-side-encryption-aws:kms header
Why this is correct
Denies unencrypted uploads.
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 SCS-C02 ACL questions on filtering logic and placement.
Data Protection — This question tests Data Protection — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: A bucket policy with a condition that denies s3:PutObject unless the request includes the x-amz-server-side-encryption-aws:kms header — Option A uses a condition to deny PutObject if encryption is not set, which enforces encryption. Option B only audits, C is too permissive, D allows unencrypted uploads.
What should I do if I get this SCS-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 SCS-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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