DEA-C01 Data Security and Governance Practice Question

A company uses AWS KMS to encrypt data in Amazon S3. The security team wants to ensure that the KMS key can only be used from within the company's VPC. Which policy element should be added to the KMS key policy?

⚠ Common exam trap

Watch out — candidates often confuse the Principal element with condition keys, or mistakenly using aws:SourceIp or kms:ViaService instead of aws:SourceVpc. Candidates often think that restricting by IP or by service is sufficient to restrict to a VPC, but only aws:SourceVpc directly validates the VPC origin.

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 condition using aws:SourceVpc to allow only requests from the VPC.

The correct approach is to add a condition using the aws:SourceVpc condition key in the KMS key policy. This condition evaluates the VPC ID from which the request originates, allowing you to restrict key usage to requests that come through a VPC endpoint within your VPC. When a request is made to KMS through a VPC endpoint, the aws:SourceVpc condition key is populated with the VPC ID, enabling precise control. This ensures that the KMS key can only be used from within the specified VPC, meeting the security team's requirement.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Set the Principal element to restrict access to the VPC.
Why it's wrong here
The Principal element names identities, not networks, so it cannot restrict key use to a VPC. It is tempting because scoping access by principal is standard policy practise, and that would be correct when limiting which IAM roles or accounts may use the key. Network restriction requires a condition element.
✗
Add a condition using aws:SourceIp to allow only IP addresses from the VPC.
Why it's wrong here
aws:SourceIp evaluates the caller's public IP, which for in-VPC traffic is often a NAT gateway address, not a VPC-internal one, so it cannot restrict key use to the VPC. It suits allow-listing known external client addresses, not enforcing VPC origin; that requires aws:SourceVpce or aws:SourceVpc.
✓
Add a condition using aws:SourceVpc to allow only requests from the VPC.
Why this is correct
Adding an `aws:SourceVpc` condition to the KMS key policy restricts key usage to requests originating from the specified VPC endpoint, satisfying the requirement that the key only be usable from within the company's VPC. This condition evaluates the VPC ID of the source, blocking access from outside the VPC.
✗
Add a condition using kms:ViaService to allow only via VPC endpoints.
Why it's wrong here
kms:ViaService restricts which AWS service may use the key on a caller's behalf, not the caller's network origin. It is tempting because it constrains key usage contextually, and that would be correct when limiting use to S3 or another integrated service. VPC restriction needs aws:SourceVpce.

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

DEA-C01 Data Security and Governance Practice Question

Why each option matters

Option-by-option breakdown

AWS S3 Storage Class Comparison

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