- A
Attach an IAM policy to the IAM roles in the member accounts that allows kms:Decrypt on the CMK.
Why wrong: Without a key policy in the security account that allows the member accounts to use the key, the IAM policy alone is insufficient because KMS requires a key policy that grants access to the principal.
- B
Add a statement to the KMS key policy that grants the IAM roles in the member accounts permission to use the key.
The key policy must explicitly allow the external accounts (or their IAM roles) to use the key. Then, the member accounts can delegate that permission to their roles via IAM policies.
- C
Create a service control policy (SCP) that allows kms:Decrypt for the CMK.
Why wrong: SCPs are used to deny permissions, not to grant them. They cannot be used to allow access to a resource.
- D
Use a VPC endpoint policy for KMS to allow access from the member accounts' VPCs.
Why wrong: VPC endpoint policies control access to the endpoint, but they do not grant permissions to use the CMK. The key policy is still required.
Quick Answer
The correct answer is to add a statement to the KMS key policy that grants the IAM roles in the member accounts permission to use the key. This is because cross-account KMS key policy for S3 encryption requires an explicit resource-based policy on the CMK itself; without it, IAM policies in the member accounts are powerless to grant access, as KMS evaluates key policies first and denies any request not explicitly allowed. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding that cross-account encryption relies on a two-part trust: the key policy must authorize the member account’s root (or specific roles), and then the member account must delegate that permission via IAM policies to its roles. A common trap is assuming an IAM policy alone suffices, or that SCPs can grant permissions—they cannot, they only deny. Memory tip: think of the key policy as the “front door” that must be unlocked before any IAM policy “room key” works.
DOP-C02 Security and Compliance Practice Question
This DOP-C02 practice question tests your understanding of security and compliance. 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 uses a centralized AWS KMS customer master key (CMK) in the security account to encrypt data in S3 buckets across multiple accounts. The S3 buckets are accessed by EC2 instances in the same accounts. The security team wants to ensure that the CMK can only be used by authorized IAM roles in the member accounts. Which policy configuration should be used?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Add a statement to the KMS key policy that grants the IAM roles in the member accounts permission to use the key.
To allow cross-account use of a KMS CMK, you must add a key policy that grants the necessary permissions to the IAM roles in the member accounts. The key policy should include a statement that allows the root user of the member accounts to delegate permissions, and then the member accounts must create IAM policies that grant their roles access. Option A is wrong because the key policy must explicitly allow the member accounts. Option B is wrong because IAM policies in the member account alone are not sufficient without a key policy allowing the account. Option C is wrong because SCPs cannot grant permissions; they only deny.
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.
- ✗
Attach an IAM policy to the IAM roles in the member accounts that allows kms:Decrypt on the CMK.
Why it's wrong here
Without a key policy in the security account that allows the member accounts to use the key, the IAM policy alone is insufficient because KMS requires a key policy that grants access to the principal.
- ✓
Add a statement to the KMS key policy that grants the IAM roles in the member accounts permission to use the key.
Why this is correct
The key policy must explicitly allow the external accounts (or their IAM roles) to use the key. Then, the member accounts can delegate that permission to their roles via IAM policies.
Related concept
Standard ACLs match source addresses.
- ✗
Create a service control policy (SCP) that allows kms:Decrypt for the CMK.
Why it's wrong here
SCPs are used to deny permissions, not to grant them. They cannot be used to allow access to a resource.
- ✗
Use a VPC endpoint policy for KMS to allow access from the member accounts' VPCs.
Why it's wrong here
VPC endpoint policies control access to the endpoint, but they do not grant permissions to use the CMK. The key policy is still required.
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 DOP-C02 ACL questions on filtering logic and placement.
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Security and Compliance — study guide chapter
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FAQ
Questions learners often ask
What does this DOP-C02 question test?
Security and Compliance — This question tests Security and Compliance — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Add a statement to the KMS key policy that grants the IAM roles in the member accounts permission to use the key. — To allow cross-account use of a KMS CMK, you must add a key policy that grants the necessary permissions to the IAM roles in the member accounts. The key policy should include a statement that allows the root user of the member accounts to delegate permissions, and then the member accounts must create IAM policies that grant their roles access. Option A is wrong because the key policy must explicitly allow the member accounts. Option B is wrong because IAM policies in the member account alone are not sufficient without a key policy allowing the account. Option C is wrong because SCPs cannot grant permissions; they only deny.
What should I do if I get this DOP-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 DOP-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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Last reviewed: Jun 20, 2026
This DOP-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DOP-C02 exam.
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