The decryption fails because the condition on kms:ViaService is not satisfied. This occurs because the KMS key policy uses the kms:ViaService condition key to restrict decryption requests exclusively to calls made through the S3 service in us-east-1, and the application is calling the KMS API directly rather than routing the request through S3. When a request arrives via the KMS API, the kms:ViaService value does not match "s3.us-east-1.amazonaws.com", so the condition evaluates to false, triggering an implicit deny. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of how service-specific condition keys enforce access paths, a common trap where candidates assume a valid principal or key policy alone grants permission. Remember that kms:ViaService is about the service endpoint used, not the identity making the call. Memory tip: think of kms:ViaService as a "service gatekeeper"—if the request doesn't come through the listed service, the gate stays closed, even if the caller has full IAM permissions.
SCS-C02 Identity and Access Management Practice Question
This SCS-C02 practice question tests your understanding of identity and access management. 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.
Refer to the exhibit. A KMS key policy allows decryption only when the request comes through S3 in us-east-1. An application in account 111122223333 tries to decrypt an S3 object using the KMS key directly via the KMS API (not through S3). What will happen?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The decryption fails because the condition on kms:ViaService is not satisfied.
Option C is correct because the condition restricts kms:ViaService to S3 in us-east-1. Since the request is made directly to KMS API, the condition is not met, resulting in implicit deny. Option A is incorrect because the condition is not satisfied. Option B is incorrect because the policy is valid. Option D is incorrect because the condition is not about the principal.
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.
✗
The decryption succeeds because the principal is the root user.
Why it's wrong here
Root user is still subject to conditions.
✗
The decryption fails because the policy is invalid.
Why it's wrong here
The policy is valid.
✗
The decryption succeeds because the principal is allowed.
Why it's wrong here
The condition must be met for the Allow to apply.
✓
The decryption fails because the condition on kms:ViaService is not satisfied.
Why this is correct
The condition requires the request to come via S3.
Related concept
Standard ACLs match source addresses.
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.
Identity and Access Management — This question tests Identity and Access Management — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The decryption fails because the condition on kms:ViaService is not satisfied. — Option C is correct because the condition restricts kms:ViaService to S3 in us-east-1. Since the request is made directly to KMS API, the condition is not met, resulting in implicit deny. Option A is incorrect because the condition is not satisfied. Option B is incorrect because the policy is valid. Option D is incorrect because the condition is not about the principal.
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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