The answer is that the KMS key policy must explicitly grant the Lambda execution role permission to use the key. Even if the IAM policy attached to the role includes the correct actions like kms:Decrypt, the key policy acts as a separate, independent access control that must allow the principal (the Lambda role) to call the KMS API. Without this explicit grant in the key policy, the Lambda function will receive an access denied error when trying to decrypt data, regardless of what the IAM policy says. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding that KMS uses a resource-based policy model where the key policy overrides IAM permissions for the key itself—a common trap is assuming IAM alone is sufficient. Remember the memory tip: "IAM says yes, but the key says no; both must agree for the crypto to flow."
DVA-C02 Security Practice Question
This DVA-C02 practice question tests your understanding of security. 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.
The exhibit shows an IAM policy attached to a Lambda function's execution role. When the Lambda function tries to decrypt data using the KMS key, it receives an access denied error. 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 key policy does not grant the Lambda execution role permission to use the key.
The policy grants kms:Decrypt but not kms:DescribeKey. However, the error is likely due to the Lambda function not having permission to call kms:Decrypt because the key's key policy might not grant the Lambda role. The key policy must explicitly allow the Lambda role to use the key. Option A is wrong because kms:Decrypt is included. Option B is wrong because it's not about kms:DescribeKey. Option C is wrong because the action list is correct. Option D is correct: the key policy must grant access to the Lambda role.
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 policy uses an incorrect action name for decryption.
Why it's wrong here
kms:Decrypt is the correct action.
✓
The KMS key policy does not grant the Lambda execution role permission to use the key.
Why this is correct
Even if the IAM policy allows, the key policy must also allow; this is a common misconfiguration.
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 policy does not include kms:DescribeKey permission.
Why it's wrong here
kms:DescribeKey is not required for decryption; the error is not about that.
✗
The policy does not include kms:Decrypt permission.
Why it's wrong here
The policy does include kms:Decrypt.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which DVA-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The KMS key policy does not grant the Lambda execution role permission to use the key. — The policy grants kms:Decrypt but not kms:DescribeKey. However, the error is likely due to the Lambda function not having permission to call kms:Decrypt because the key's key policy might not grant the Lambda role. The key policy must explicitly allow the Lambda role to use the key. Option A is wrong because kms:Decrypt is included. Option B is wrong because it's not about kms:DescribeKey. Option C is wrong because the action list is correct. Option D is correct: the key policy must grant access to the Lambda role.
What should I do if I get this DVA-C02 question wrong?
Identify which DVA-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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