The correct answer is to add a condition using aws:SourceVpc with the value vpc-12345678 to the existing 'Allow use of the key' statement in the key policy. This works because the aws:SourceVpc condition key evaluates the originating VPC of the API request, effectively restricting all KMS operations to traffic that originates from within the specified VPC, regardless of the IAM role or user making the call. On the AWS Certified Security Specialty SCS-C02 exam, this question tests your understanding of KMS key policies versus IAM policies, and the common trap is confusing aws:SourceVpc with kms:ViaService, which only restricts to a specific AWS service endpoint (like S3) rather than the VPC itself. Remember that aws:SourceVpc locks down the network origin, while kms:ViaService locks down the service path—a key distinction for network-based key restrictions. A helpful memory tip is "VPC for the pipe, ViaService for the service."
SCS-C02 Data Protection Practice Question
This SCS-C02 practice question tests your understanding of data protection. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
Network Topology
Refer to the exhibit. A security engineer is reviewing the key policy for a customer managed key. The engineer notices that a user with the IAM role 'Admin' can encrypt and decrypt data using this key. However, the engineer wants to ensure that only requests coming from the company's VPC (vpc-12345678) can use the key. What should be added to the key policy?
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 aws:SourceVpc with value vpc-12345678 to the 'Allow use of the key' statement
To restrict key usage to a VPC, you need to add a condition to the key policy using the aws:SourceVpc key. Option B is correct. Option A is incorrect because the condition should be added to the existing statements, not a new statement. Option C is incorrect because kms:ViaService restricts to a service endpoint, not a VPC. Option D is incorrect because kms:CallerAccount is not relevant.
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.
✗
Add a condition kms:ViaService with value s3.amazonaws.com
Why it's wrong here
Restricts to service endpoint, not VPC.
✗
Add a condition kms:CallerAccount with value 111122223333
Why it's wrong here
Does not restrict to VPC.
✓
Add a condition aws:SourceVpc with value vpc-12345678 to the 'Allow use of the key' statement
Why this is correct
Restricts access to requests from the specified VPC.
Related concept
Standard ACLs match source addresses.
✗
Add a new statement with Effect: Deny and a condition aws:SourceVpc not equal to vpc-12345678
Why it's wrong here
Deny statements are less secure; better to allow only from VPC.
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: Add a condition aws:SourceVpc with value vpc-12345678 to the 'Allow use of the key' statement — To restrict key usage to a VPC, you need to add a condition to the key policy using the aws:SourceVpc key. Option B is correct. Option A is incorrect because the condition should be added to the existing statements, not a new statement. Option C is incorrect because kms:ViaService restricts to a service endpoint, not a VPC. Option D is incorrect because kms:CallerAccount is not relevant.
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.
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Question Discussion
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