The answer is to create a KMS key policy that grants only the specific IAM role the `kms:Decrypt` permission. This is the most secure approach because a KMS key policy acts as the primary access control for the customer master key (CMK), directly binding the decryption permission to the key itself rather than relying on IAM policies that can be attached to multiple identities. By explicitly restricting the `kms:Decrypt` action in the key policy to a single role, you prevent any other principal—including the AWS account root user or other roles with broad IAM permissions—from decrypting the data, effectively decoupling data access from infrastructure access. On the AWS Certified Developer Associate DVA-C02 exam, this tests your understanding of the KMS authorization model, where key policies take precedence over IAM policies for cryptographic operations; a common trap is assuming an IAM policy alone can override a restrictive key policy. Memory tip: think of the key policy as the bouncer at the door—only the role on the guest list gets the decrypt pass.
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.
A company is using AWS KMS to encrypt sensitive data stored in S3. The security team wants to ensure that only a specific IAM role can decrypt the data. What is the most secure way to achieve this?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a KMS key policy that grants the role the kms:Decrypt permission.
Option B is correct because KMS key policies are the most direct and secure way to control who can perform cryptographic operations like kms:Decrypt on a specific CMK. By granting only the specific IAM role the kms:Decrypt permission in the key policy, you ensure that no other principal (including the root user or other roles) can decrypt the data, even if they have S3 access. This follows the principle of least privilege and decouples data access from infrastructure access.
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.
✗
Use S3 server-side encryption with S3-managed keys (SSE-S3).
Why it's wrong here
SSE-S3 does not allow customer-specific access control.
✓
Create a KMS key policy that grants the role the kms:Decrypt permission.
Why this is correct
KMS key policies directly control who can use the key.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable automatic key rotation for the KMS key.
Why it's wrong here
Key rotation does not restrict decryption permissions.
✗
Use an S3 bucket policy to restrict access to the role.
Why it's wrong here
S3 bucket policies control S3 operations, not KMS decryption.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse S3 bucket policies with KMS key policies, assuming that restricting S3 access is sufficient to prevent decryption, when in fact the KMS key policy is the only way to enforce decryption restrictions at the cryptographic level.
Detailed technical explanation
How to think about this question
KMS key policies are resource-based policies that define who can use the key and under what conditions. When a principal calls kms:Decrypt, KMS evaluates both the key policy and any IAM policies attached to the principal; the key policy must explicitly grant the action, and if it does not, the request is denied regardless of IAM permissions. This is critical in multi-account or cross-service scenarios where you want to ensure that even an administrator with full S3 access cannot decrypt the data without the specific role assuming the correct permissions.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Create a KMS key policy that grants the role the kms:Decrypt permission. — Option B is correct because KMS key policies are the most direct and secure way to control who can perform cryptographic operations like kms:Decrypt on a specific CMK. By granting only the specific IAM role the kms:Decrypt permission in the key policy, you ensure that no other principal (including the root user or other roles) can decrypt the data, even if they have S3 access. This follows the principle of least privilege and decouples data access from infrastructure access.
What should I do if I get this DVA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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