The answer is to use a KMS key policy that explicitly limits key users and administrators, combined with IAM policies that grant kms:Decrypt only to required application roles. This works because the key policy acts as the primary access control for the KMS key itself, overriding any broader IAM permissions; even if a principal has full IAM access, they cannot invoke KMS operations unless the key policy explicitly allows them. On the SAA-C03 exam, this tests your understanding that KMS key policies are resource-based and take precedence over identity-based IAM policies, a common trap where students assume IAM alone is sufficient. A frequent distractor is suggesting S3 bucket policies, but those control S3 access, not the key directly. Remember the memory tip: “Key policy is the gatekeeper; IAM is just the visitor list.”
SAA-C03 Design Secure Architectures Practice Question
This SAA-C03 practice question tests your understanding of design secure architectures. 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 encrypting sensitive S3 data for a mobile banking backend with AWS KMS. Which two controls help prevent accidental use of the KMS key by unauthorized principals?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A key policy that limits key administrators and key users
Option B is correct because a KMS key policy explicitly defines which principals (IAM users, roles, AWS accounts) can administer or use the key. By limiting key administrators and key users in the key policy, you prevent unauthorized principals from accidentally invoking KMS operations on that key, even if they have broad IAM permissions. This is a direct access control mechanism at the key level.
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.
✗
A larger KMS key rotation period
Why it's wrong here
Rotation interval does not determine which principals may use a key.
✓
A key policy that limits key administrators and key users
Why this is correct
The KMS key policy is the primary resource policy that controls who can administer or use the key.
Related concept
Read the scenario before looking for a memorised answer.
✗
S3 Transfer Acceleration
Why it's wrong here
Transfer Acceleration does not control KMS key usage.
✓
IAM policies that grant kms:Decrypt only to required application roles
Why this is correct
IAM permissions should grant least-privilege use of the KMS key to specific roles.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think IAM policies alone are sufficient for KMS access control, but they forget that KMS key policies are evaluated first and can explicitly deny or limit access regardless of IAM permissions.
Detailed technical explanation
How to think about this question
KMS key policies are resource-based policies that work in conjunction with IAM policies; for a principal to use a KMS key, both the key policy must grant the action (e.g., kms:Decrypt) to that principal (or allow the account to delegate via IAM) and the IAM policy must also allow it. The key policy can explicitly deny all principals except a specific set, creating a strong boundary that overrides any IAM permissions. In practice, this prevents scenarios where a developer with broad IAM permissions accidentally uses a key meant only for production.
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.
Design Secure Architectures — This question tests Design Secure Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: A key policy that limits key administrators and key users — Option B is correct because a KMS key policy explicitly defines which principals (IAM users, roles, AWS accounts) can administer or use the key. By limiting key administrators and key users in the key policy, you prevent unauthorized principals from accidentally invoking KMS operations on that key, even if they have broad IAM permissions. This is a direct access control mechanism at the key level.
What should I do if I get this SAA-C03 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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