- A
In the KMS key policy, allowing kms:Decrypt (and any other required KMS permissions) for the role’s principal ARN.
With SSE-KMS, KMS decryption is authorized by KMS for the specific CMK. The CMK key policy is a primary authorization layer; if the key policy does not allow kms:Decrypt for the role (or a matching principal), S3 requests that require KMS decryption will fail even if the S3 or IAM identity policies allow s3:GetObject.
- B
Only in the S3 bucket policy by granting s3:GetObject, because S3 bucket policy controls decryption.
Why wrong: An S3 bucket policy can authorize s3:GetObject, but it does not grant KMS permission to decrypt a KMS-encrypted data key. KMS will still require key-policy (and IAM) authorization for kms:Decrypt on the CMK.
- C
Only in the IAM role identity policy; the KMS key policy does not need changes for SSE-KMS.
Why wrong: For customer-managed keys, a restrictive CMK key policy can deny or omit access. In that case, identity-policy kms:Decrypt permission alone is insufficient because the key policy is also evaluated and must allow the role to use the key for decryption.
- D
By enabling S3 default encryption; KMS permissions are automatically granted to all IAM roles in the account.
Why wrong: Default encryption only ensures objects are encrypted with the specified CMK when written. It does not grant decrypt permissions to other principals. Roles must be explicitly authorized to use the CMK.
Quick Answer
The answer is the KMS key policy. When you use a customer managed KMS key for SSE-KMS, the key policy is the authoritative access control for the key itself, meaning you must explicitly grant kms:Decrypt permission to the IAM role’s principal ARN within that policy. Even if the role has s3:GetObject on the bucket, KMS enforces its own authorization separately, so without this key policy entry, decryption will fail. On the SAA-C03 exam, this tests your understanding that KMS and S3 permissions are independent layers—a common trap is assuming S3 bucket policies alone suffice for SSE-KMS decryption. Remember the memory tip: “S3 opens the door, KMS unlocks the box”—you need both permissions, but the decrypt permission lives in the key policy for customer managed keys.
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.
You use a customer managed AWS KMS key (CMK) to encrypt objects in an S3 bucket using SSE-KMS. A specific IAM role must be able to decrypt objects. Where should you grant kms:Decrypt permissions so that the role can decrypt data encrypted with that CMK?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
In the KMS key policy, allowing kms:Decrypt (and any other required KMS permissions) for the role’s principal ARN.
When using a customer managed KMS key (CMK) with SSE-KMS, the KMS key policy is the primary access control mechanism. To allow a specific IAM role to decrypt objects, you must grant kms:Decrypt (and typically kms:DescribeKey) in the key policy for that role's principal ARN. Without this explicit permission in the key policy, the role will be denied decryption even if it has s3:GetObject permissions, because KMS enforces its own authorization.
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.
- ✓
In the KMS key policy, allowing kms:Decrypt (and any other required KMS permissions) for the role’s principal ARN.
Why this is correct
With SSE-KMS, KMS decryption is authorized by KMS for the specific CMK. The CMK key policy is a primary authorization layer; if the key policy does not allow kms:Decrypt for the role (or a matching principal), S3 requests that require KMS decryption will fail even if the S3 or IAM identity policies allow s3:GetObject.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Only in the S3 bucket policy by granting s3:GetObject, because S3 bucket policy controls decryption.
Why it's wrong here
An S3 bucket policy can authorize s3:GetObject, but it does not grant KMS permission to decrypt a KMS-encrypted data key. KMS will still require key-policy (and IAM) authorization for kms:Decrypt on the CMK.
- ✗
Only in the IAM role identity policy; the KMS key policy does not need changes for SSE-KMS.
Why it's wrong here
For customer-managed keys, a restrictive CMK key policy can deny or omit access. In that case, identity-policy kms:Decrypt permission alone is insufficient because the key policy is also evaluated and must allow the role to use the key for decryption.
- ✗
By enabling S3 default encryption; KMS permissions are automatically granted to all IAM roles in the account.
Why it's wrong here
Default encryption only ensures objects are encrypted with the specified CMK when written. It does not grant decrypt permissions to other principals. Roles must be explicitly authorized to use the CMK.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume S3 bucket policies or IAM identity policies alone are sufficient for decryption, forgetting that KMS enforces its own authorization layer and the key policy is the gatekeeper for all KMS operations.
Detailed technical explanation
How to think about this question
Under the hood, when S3 receives a GET request for an SSE-KMS encrypted object, it calls KMS Decrypt with the encrypted data key. KMS evaluates the key policy, any grants, and IAM policies (if the key policy allows IAM policies) to authorize the request. A common real-world scenario is cross-account access: you must add the external account's root principal in the key policy and then grant the specific IAM role permissions via an IAM policy in that account, because key policies cannot reference cross-account role ARNs 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 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.
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
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: In the KMS key policy, allowing kms:Decrypt (and any other required KMS permissions) for the role’s principal ARN. — When using a customer managed KMS key (CMK) with SSE-KMS, the KMS key policy is the primary access control mechanism. To allow a specific IAM role to decrypt objects, you must grant kms:Decrypt (and typically kms:DescribeKey) in the key policy for that role's principal ARN. Without this explicit permission in the key policy, the role will be denied decryption even if it has s3:GetObject permissions, because KMS enforces its own authorization.
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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Last reviewed: Jun 11, 2026
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.
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