The answer is to modify the KMS key policy to allow only the intended IAM role and explicitly deny all others. This is correct because KMS key policies are resource-based policies that directly control who can use the key, and by specifying the intended role’s ARN in an Allow statement while adding a Deny statement for all other principals, you create a definitive restriction that overrides any broader IAM permissions. On the AWS Certified Security Specialty SCS-C02 exam, this tests your understanding of the difference between key policies and IAM policies—a common trap is assuming an S3 bucket policy can restrict KMS usage, but KMS key operations are governed solely by the key policy or IAM policies combined with the key policy’s trust. To remember, think “key policy is the gatekeeper”: if you want to restrict a KMS key to a specific IAM role, you must lock the gate at the key itself, not at the service using it.
SCS-C02 Data Protection Practice Question
This SCS-C02 practice question tests your understanding of data protection. 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 AWS KMS with a customer managed key to encrypt an S3 bucket. The security team notices that the KMS key is being used by an unintended IAM role. What is the MOST effective way to restrict the key usage to only the intended role?
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 allow only the intended role and deny all others
Using a KMS key policy with a condition on kms:CallerArn is the most effective. Option A is wrong because the key policy already exists and you cannot remove the default key policy. Option B is wrong because the original key policy may have allowed broad access. Option D is wrong because S3 bucket policy does not control KMS key usage.
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.
✗
Remove the default key policy and attach an IAM policy to the intended role
Why it's wrong here
The default key policy cannot be removed; also IAM policy alone cannot restrict key usage if key policy allows it.
✗
Use an S3 bucket policy to restrict access to the intended role
Why it's wrong here
Bucket policy does not control KMS key usage.
✓
Modify the key policy to allow only the intended role and deny all others
Why this is correct
A key policy can explicitly allow only the intended role.
Related concept
Standard ACLs match source addresses.
✗
Create a new KMS key and attach a new key policy
Why it's wrong here
This is a less effective solution as it does not restrict the existing key.
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: Modify the key policy to allow only the intended role and deny all others — Using a KMS key policy with a condition on kms:CallerArn is the most effective. Option A is wrong because the key policy already exists and you cannot remove the default key policy. Option B is wrong because the original key policy may have allowed broad access. Option D is wrong because S3 bucket policy does not control KMS key usage.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company stores sensitive data in an S3 bucket and uses AWS KMS to encrypt the data. The security team wants to ensure that only specific IAM roles can decrypt the data. What should the team do?
medium
A.Use a KMS grant to allow the roles to decrypt the key.
✓ B.Modify the KMS key policy to include a condition that allows kms:Decrypt only for the specific IAM roles.
C.Attach an IAM policy to the roles that allows kms:Decrypt on the key.
D.Add an S3 bucket policy that denies s3:GetObject for all roles except the allowed ones.
Why B: Option D is correct because using a KMS key policy that grants kms:Decrypt only to the specific roles ensures that only those roles can decrypt. Option A is wrong because an S3 bucket policy controls access to S3 operations, not KMS decryption. Option B is wrong because an IAM policy that allows kms:Decrypt for all users would not restrict to specific roles. Option C is wrong because a KMS grant is a temporary permission, not a permanent policy.
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This SCS-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 SCS-C02 exam.
Question Discussion
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