- A
Add kms:Decrypt only to the Account B role’s IAM policy, without changing the customer-managed KMS key policy in Account A.
Why wrong: For a customer-managed KMS key, KMS authorization is enforced by both the IAM identity policy (for the role) and the KMS key policy. If the key policy does not allow the Account B principal to use the key, kms:Decrypt will still be denied.
- B
Update the Account A S3 bucket policy to grant kms:Decrypt to Account B.
Why wrong: S3 bucket policies control access to S3 operations (like s3:GetObject). They do not grant permissions to KMS for SSE-KMS decryption; KMS key policy or grants must allow kms:Decrypt.
- C
Update the customer-managed KMS key policy in Account A to allow kms:Decrypt for the specific Account B role principal.
With SSE-KMS, S3 calls KMS on your behalf during decryption. KMS checks the customer-managed key policy (and optionally grants). Allowing the Account B role principal in the KMS key policy for kms:Decrypt directly resolves KMS AccessDenied.
- D
Enable KMS key rotation, which automatically allows cross-account decrypt permissions.
Why wrong: Key rotation changes key material over time but does not modify which principals are authorized to use the key. It does not grant kms:Decrypt permission to Account B.
SAA-C03 Design Secure Architectures Practice Question
This SAA-C03 practice question tests your understanding of design secure architectures. 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.
A cross-account IAM role in Account B reads encrypted S3 objects from Account A. The objects use SSE-KMS with a customer-managed KMS key in Account A. Account B can successfully call s3:GetObject, but decryption fails with an AccessDeniedException from KMS. What change most directly fixes the issue?
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
Update the customer-managed KMS key policy in Account A to allow kms:Decrypt for the specific Account B role principal.
SSE-KMS with a customer-managed KMS key requires explicit permission to use the key for decryption. The S3 GetObject call succeeds because the bucket policy allows it, but KMS decryption fails because the KMS key policy in Account A does not grant kms:Decrypt to the IAM role principal in Account B. Updating the KMS key policy to allow the Account B role principal to call kms:Decrypt directly resolves the AccessDeniedException.
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.
- ✗
Add kms:Decrypt only to the Account B role’s IAM policy, without changing the customer-managed KMS key policy in Account A.
Why it's wrong here
For a customer-managed KMS key, KMS authorization is enforced by both the IAM identity policy (for the role) and the KMS key policy. If the key policy does not allow the Account B principal to use the key, kms:Decrypt will still be denied.
- ✗
Update the Account A S3 bucket policy to grant kms:Decrypt to Account B.
Why it's wrong here
S3 bucket policies control access to S3 operations (like s3:GetObject). They do not grant permissions to KMS for SSE-KMS decryption; KMS key policy or grants must allow kms:Decrypt.
- ✓
Update the customer-managed KMS key policy in Account A to allow kms:Decrypt for the specific Account B role principal.
Why this is correct
With SSE-KMS, S3 calls KMS on your behalf during decryption. KMS checks the customer-managed key policy (and optionally grants). Allowing the Account B role principal in the KMS key policy for kms:Decrypt directly resolves KMS AccessDenied.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Enable KMS key rotation, which automatically allows cross-account decrypt permissions.
Why it's wrong here
Key rotation changes key material over time but does not modify which principals are authorized to use the key. It does not grant kms:Decrypt permission to Account B.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume S3 bucket policies can control KMS permissions, but KMS key policies are the sole mechanism for granting cross-account access to customer-managed keys, and IAM policies alone are insufficient for cross-account KMS operations.
Detailed technical explanation
How to think about this question
When using SSE-KMS with a customer-managed key, the S3 service calls KMS on behalf of the requesting principal to decrypt the object. For cross-account access, the KMS key policy must include a statement that allows the external IAM role principal to perform kms:Decrypt (and optionally kms:GenerateDataKey for new uploads). Without this, even if the S3 bucket policy allows GetObject, the KMS call fails with AccessDenied. A common real-world scenario is granting cross-account read access to encrypted data in a data lake, where the key policy must be updated before the consumer can decrypt.
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: Update the customer-managed KMS key policy in Account A to allow kms:Decrypt for the specific Account B role principal. — SSE-KMS with a customer-managed KMS key requires explicit permission to use the key for decryption. The S3 GetObject call succeeds because the bucket policy allows it, but KMS decryption fails because the KMS key policy in Account A does not grant kms:Decrypt to the IAM role principal in Account B. Updating the KMS key policy to allow the Account B role principal to call kms:Decrypt directly resolves the AccessDeniedException.
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
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