- A
Add kms:Decrypt to the KMS key policy in Account A for the Account B role arn:aws:iam::account-b:role/app-read, and remove kms:Decrypt from the role policy in Account B.
Why wrong: Adding kms:Decrypt to the KMS key policy is a valid approach, but removing kms:Decrypt from the role policy is not required to fix an AccessDenied kms:Decrypt failure. KMS authorization requires both (1) identity policy permission (in Account B) and (2) the KMS key policy permission (in Account A). Removing the role permission can cause the failure to continue or move to a different authorization denial.
- B
Update the IAM role in Account B to use the s3:GetObject permission only, and rely on S3 to authorize KMS decrypt automatically.
Why wrong: S3 authorization to call GetObject does not eliminate the need for KMS permissions to call kms:Decrypt. For SSE-KMS, the GetObject request ultimately requires kms:Decrypt in KMS, which is authorized by both the caller’s IAM permissions and the KMS key policy.
- C
Modify the KMS key policy in Account A to allow kms:Decrypt for the Account B role arn:aws:iam::account-b:role/app-read, using the appropriate cross-account conditions (for example, allowing the use via S3 and the expected encryption context for the bucket).
For SSE-KMS, S3 must call KMS Decrypt when serving objects. KMS authorization is evaluated against the KMS key policy in Account A in addition to the identity policy in Account B. If the error includes kms:Decrypt AccessDenied in a cross-account scenario, the most direct fix is to update the KMS key policy to allow the Account B role to use the key for decrypt (often with conditions tied to S3 usage and the specific bucket/object encryption context).
- D
Switch the S3 bucket encryption from SSE-KMS to SSE-S3, keeping all existing IAM and KMS configuration unchanged.
Why wrong: Changing to SSE-S3 avoids KMS decryption entirely, so it could remove the kms:Decrypt failure. However, that is not a targeted fix for the underlying authorization issue and conflicts with the stated requirement of using the existing customer-managed KMS key for SSE-KMS.
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.
An application in Account B (IAM role arn:aws:iam::account-b:role/app-read) reads objects from an S3 bucket in Account A. The bucket uses SSE-KMS with a customer-managed KMS key in Account A. Object reads consistently fail with an error that includes "AccessDenied" and "kms:Decrypt".
The IAM permissions in Account B for kms:Decrypt are correct, but the requests still fail.
Which change will most directly fix the failure?
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
Modify the KMS key policy in Account A to allow kms:Decrypt for the Account B role arn:aws:iam::account-b:role/app-read, using the appropriate cross-account conditions (for example, allowing the use via S3 and the expected encryption context for the bucket).
Option C is correct because when using SSE-KMS with a customer-managed KMS key in a cross-account scenario, the KMS key policy must explicitly grant the external IAM role (arn:aws:iam::account-b:role/app-read) permission to perform kms:Decrypt. Even if the IAM role in Account B has the correct kms:Decrypt permission, the KMS key policy in Account A acts as a resource-based policy that must also allow the cross-account principal. Without this, the KMS service denies the decrypt request, resulting in the 'AccessDenied' error.
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 to the KMS key policy in Account A for the Account B role arn:aws:iam::account-b:role/app-read, and remove kms:Decrypt from the role policy in Account B.
Why it's wrong here
Adding kms:Decrypt to the KMS key policy is a valid approach, but removing kms:Decrypt from the role policy is not required to fix an AccessDenied kms:Decrypt failure. KMS authorization requires both (1) identity policy permission (in Account B) and (2) the KMS key policy permission (in Account A). Removing the role permission can cause the failure to continue or move to a different authorization denial.
- ✗
Update the IAM role in Account B to use the s3:GetObject permission only, and rely on S3 to authorize KMS decrypt automatically.
Why it's wrong here
S3 authorization to call GetObject does not eliminate the need for KMS permissions to call kms:Decrypt. For SSE-KMS, the GetObject request ultimately requires kms:Decrypt in KMS, which is authorized by both the caller’s IAM permissions and the KMS key policy.
- ✓
Modify the KMS key policy in Account A to allow kms:Decrypt for the Account B role arn:aws:iam::account-b:role/app-read, using the appropriate cross-account conditions (for example, allowing the use via S3 and the expected encryption context for the bucket).
Why this is correct
For SSE-KMS, S3 must call KMS Decrypt when serving objects. KMS authorization is evaluated against the KMS key policy in Account A in addition to the identity policy in Account B. If the error includes kms:Decrypt AccessDenied in a cross-account scenario, the most direct fix is to update the KMS key policy to allow the Account B role to use the key for decrypt (often with conditions tied to S3 usage and the specific bucket/object encryption context).
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Switch the S3 bucket encryption from SSE-KMS to SSE-S3, keeping all existing IAM and KMS configuration unchanged.
Why it's wrong here
Changing to SSE-S3 avoids KMS decryption entirely, so it could remove the kms:Decrypt failure. However, that is not a targeted fix for the underlying authorization issue and conflicts with the stated requirement of using the existing customer-managed KMS key for SSE-KMS.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume IAM permissions alone are sufficient for cross-account KMS operations, forgetting that KMS key policies are resource-based and must explicitly allow external principals, even when the IAM role has the correct permissions.
Detailed technical explanation
How to think about this question
Under the hood, KMS uses a resource-based key policy that controls access to the key, separate from IAM policies. For cross-account access, the key policy must explicitly list the external IAM role ARN as a principal, and the role must have the corresponding IAM permission (kms:Decrypt) to use the key. Additionally, S3 automatically passes an encryption context (e.g., bucket ARN and object path) to KMS during decrypt; the key policy can optionally enforce this context via conditions like kms:EncryptionContext:aws:s3:arn for added security.
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
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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: Modify the KMS key policy in Account A to allow kms:Decrypt for the Account B role arn:aws:iam::account-b:role/app-read, using the appropriate cross-account conditions (for example, allowing the use via S3 and the expected encryption context for the bucket). — Option C is correct because when using SSE-KMS with a customer-managed KMS key in a cross-account scenario, the KMS key policy must explicitly grant the external IAM role (arn:aws:iam::account-b:role/app-read) permission to perform kms:Decrypt. Even if the IAM role in Account B has the correct kms:Decrypt permission, the KMS key policy in Account A acts as a resource-based policy that must also allow the cross-account principal. Without this, the KMS service denies the decrypt request, resulting in the 'AccessDenied' error.
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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