SCS-C02 Data Protection Practice Question
A company uses AWS KMS to encrypt data in Amazon S3. Security team wants to ensure that only specific IAM roles can decrypt objects. Which KMS key 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
✓
In the key policy, use a Condition block with kms:ViaService set to s3.<region>.amazonaws.com and allow kms:Decrypt for the role.
Using a kms:ViaService condition in the key policy restricts the key usage to requests coming from Amazon S3, and the IAM role's permissions to decrypt are granted via the key policy, ensuring only that role can decrypt via S3. Option A is wrong because without the key policy granting decrypt to the role, the IAM policy alone is insufficient. Option B is wrong because it grants blanket decrypt access to the role without the S3 service restriction, allowing decryption outside S3. Option C is wrong because grants are not the recommended way to control access for IAM roles with S3; key policies with conditions are more appropriate.
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 role that allows kms:Decrypt, and leave the KMS key policy with default settings.
Why it's wrong here
Default key policy grants account root full access; the role would still need the key policy to allow decrypt.
- ✗
In the key policy, use a Principal element specifying the role ARN, and allow kms:Decrypt.
Why it's wrong here
This allows decrypt from any service, not just S3; the requirement is to restrict to S3.
- ✗
Use a grant for the role to allow kms:Decrypt for S3 operations.
Why it's wrong here
Grants are used for delegated administration, not for restricting usage to a specific service.
- ✓
In the key policy, use a Condition block with kms:ViaService set to s3.<region>.amazonaws.com and allow kms:Decrypt for the role.
Why this is correct
This restricts decryption requests to come via S3 service, meeting the requirement.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.