This CCSP practice question tests your understanding of cloud data security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
An administrator configured the above key policy for a KMS key used to encrypt S3 backup data. The backup role 'BackupRole' is in the same account. However, when the backup service attempts to use the key to decrypt objects, the operation fails. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'kms:ViaService' condition restricts calls to those originating from S3, but the backup service uses direct KMS API
The 'kms:ViaService' condition key restricts KMS API calls to those that originate from a specific AWS service, in this case S3. However, the backup service is likely making direct KMS API calls (e.g., Decrypt) rather than having S3 proxy the request, so the condition fails. The key policy explicitly denies access unless the call comes via S3, which is why decryption fails.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 principal ARN is incorrect because the role name contains uppercase letters
Why it's wrong here
ARNs are case-sensitive, but the role name appears correct.
✓
The 'kms:ViaService' condition restricts calls to those originating from S3, but the backup service uses direct KMS API
Why this is correct
The condition prevents direct KMS calls.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The key policy requires a grant token that is not being provided
Why it's wrong here
No grant token required in this policy.
✗
The action list does not include 'kms:Decrypt' for S3
Why it's wrong here
Decrypt is included.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the nuance that 'kms:ViaService' only applies when the request is made through the specified service's integration, not when the client calls KMS directly, leading candidates to overlook the direct API call scenario.
Detailed technical explanation
How to think about this question
The 'kms:ViaService' condition key works by checking the service principal that made the initial request; when S3 calls KMS on behalf of a user or role, the request is tagged as coming via S3. If a service like AWS Backup uses the KMS API directly (e.g., via the AWS SDK or CLI) to decrypt objects, the request lacks the S3 service context, causing the condition to evaluate to false. This is a common misconfiguration when administrators assume all decryption requests will be proxied through S3, but backup tools often call KMS directly.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Cloud Data Security — This question tests Cloud Data Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The 'kms:ViaService' condition restricts calls to those originating from S3, but the backup service uses direct KMS API — The 'kms:ViaService' condition key restricts KMS API calls to those that originate from a specific AWS service, in this case S3. However, the backup service is likely making direct KMS API calls (e.g., Decrypt) rather than having S3 proxy the request, so the condition fails. The key policy explicitly denies access unless the call comes via S3, which is why decryption fails.
What should I do if I get this CCSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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