DEA-C01 Data Store Management Practice Question
Exhibit
Refer to the exhibit.
```
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": ["kms:Decrypt", "kms:Encrypt"],
"Resource": "arn:aws:kms:us-east-1:123456789012:key/abc123"
},
{
"Effect": "Deny",
"Action": ["kms:Decrypt"],
"Resource": "arn:aws:kms:us-east-1:123456789012:key/abc123",
"Condition": {
"StringNotEquals": {
"kms:ViaService": "s3.us-east-1.amazonaws.com"
}
}
}
]
}
```Refer to the exhibit. An IAM policy is attached to an IAM role used by an application. The application needs to decrypt objects in an S3 bucket using a customer managed KMS key. What is the effect of this policy?
⚠ Common exam trap
AWS often tests the `kms:ViaService` condition key to trap candidates who assume that granting `kms:Decrypt` alone allows decryption from any source, ignoring the service-specific restriction.
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
✓
The application can decrypt objects only when accessing them through S3.
The IAM policy grants the `kms:Decrypt` permission with a `kms:ViaService` condition key set to `s3.amazonaws.com`. This condition restricts the decryption operation to only when the request is made through the S3 service. Therefore, the application can decrypt objects only when accessing them through S3, not via direct KMS API calls or other services.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The application cannot perform any KMS operations.
Why it's wrong here
The attached policy does allow KMS actions, so the application is not wholly blocked; the limitation is the specific action set granted. It is tempting because a policy denying or omitting kms:Decrypt would produce exactly this outcome, but the exhibit grants encrypt permissions rather than none.
- ✗
The application can decrypt objects from any service.
Why it's wrong here
KMS key policies and IAM policies scope permissions to specific key ARNs, so a grant on one customer managed key cannot authorise decryption through every service. It is tempting because identity-based policies can be broad, but resource-based key policies still constrain which principals may use each key.
- ✓
The application can decrypt objects only when accessing them through S3.
Why this is correct
The policy grants kms:Decrypt but conditions it on the request arriving via the S3 service, so the principal can decrypt only through S3 GetObject calls. Direct KMS decrypt requests, or access via other services, are denied by the condition.
- ✗
The application can encrypt but not decrypt objects.
Why it's wrong here
The policy grants kms:Encrypt without kms:Decrypt, so decryption of the customer managed key fails regardless of S3 permissions. It is tempting because encryption-only roles are legitimate for write-only ingestion pipelines that never read data back, but this application must decrypt existing objects.
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
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