The correct answer is to modify the key policy to remove any statements that allow access from external AWS accounts. This works because AWS KMS uses resource-based policies (key policies) as the primary access control mechanism; unlike IAM policies, which grant permissions within your account, a key policy can explicitly allow or deny access to principals from other AWS accounts. To restrict KMS key usage to your own AWS account, you must ensure the key policy contains no `Principal` element referencing an external account ID or an organization outside your control. On the AWS Certified Developer Associate DVA-C02 exam, this tests your understanding of the difference between key policies and IAM policies—a common trap is assuming an IAM policy alone can block external access when the key policy still grants it. Remember the memory tip: "Key policy is the gatekeeper; IAM is just the keychain."
DVA-C02 Security Practice Question
This DVA-C02 practice question tests your understanding of security. 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 company is using AWS Key Management Service (KMS) to encrypt data in S3. The security team wants to ensure that only the company's AWS account can access the KMS key. What should be done?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Modify the key policy to remove any statements that allow access from external AWS accounts.
Option C is correct because modifying the key policy to deny access to external accounts ensures only the own account can use the key. Option A is wrong because IAM policies alone cannot prevent access if the key policy grants access to others. Option B is wrong because disabling the key prevents all use. Option D is wrong because S3 bucket policies do not control KMS key access.
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.
✗
Disable the KMS key and re-enable it only when needed.
Why it's wrong here
This prevents all use, not just external.
✓
Modify the key policy to remove any statements that allow access from external AWS accounts.
Why this is correct
Key policies control access to the key.
Related concept
Standard ACLs match source addresses.
✗
Use an S3 bucket policy to deny access to any user not from the company's account.
Why it's wrong here
Bucket policy does not control KMS key access.
✗
Attach an IAM policy to the key that denies access to external accounts.
Why it's wrong here
IAM policies cannot be attached to KMS keys; key policies are used.
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 DVA-C02 ACL questions on filtering logic and placement.
Security — This question tests Security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Modify the key policy to remove any statements that allow access from external AWS accounts. — Option C is correct because modifying the key policy to deny access to external accounts ensures only the own account can use the key. Option A is wrong because IAM policies alone cannot prevent access if the key policy grants access to others. Option B is wrong because disabling the key prevents all use. Option D is wrong because S3 bucket policies do not control KMS key access.
What should I do if I get this DVA-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 DVA-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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