- A
Update the KMS key policy to allow kms:Decrypt for the service role principal (or the assumed-role principal identity that the KMS key evaluates).
KMS authorization is controlled by the KMS key policy in addition to (not instead of) IAM identity policies. If the key policy does not allow the principal, KMS will deny kms:Decrypt even if the IAM policy allows it.
- B
Add an IAM policy statement allowing s3:GetObject for the bucket that stores the encrypted data.
Why wrong: S3 permissions determine whether the encrypted ciphertext can be retrieved. They do not grant cryptographic authorization to call kms:Decrypt on the KMS key.
- C
Enable a CloudFront distribution for the KMS key alias.
Why wrong: CloudFront settings and distribution behavior do not affect KMS key policy evaluation for kms:Decrypt.
- D
Create a VPC gateway endpoint for KMS to route decryption requests privately.
Why wrong: Private networking can affect connectivity, but it cannot replace authorization. Without key-policy permission, KMS will still deny kms:Decrypt with AccessDenied.
Quick Answer
The answer is to update the KMS key policy to allow kms:Decrypt for the service role principal or its assumed-role ARN. This is correct because AWS KMS evaluates authorization using a combination of key policies and IAM policies, but when a key policy exists, it acts as the primary gatekeeper—if the key policy does not explicitly grant the role permission, the IAM policy alone is insufficient, and KMS returns an AccessDenied error. On the SAA-C03 exam, this scenario tests your understanding of the KMS authorization model, where a common trap is assuming an IAM policy alone grants access to a customer-managed key; in reality, the key policy must include the principal. A helpful memory tip is “key policy is king”—if a key policy is present, it must explicitly allow the role, or access is denied.
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 service role has an IAM policy granting kms:Decrypt for a specific AWS KMS key. The application still fails to decrypt with an AccessDenied error. What change most directly fixes this when the KMS key policy is missing the role’s permissions?
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 KMS key policy to allow kms:Decrypt for the service role principal (or the assumed-role principal identity that the KMS key evaluates).
The AccessDenied error occurs because the KMS key policy does not grant the service role (or its assumed-role principal) permission to call kms:Decrypt. Even if the IAM policy attached to the role allows kms:Decrypt, KMS requires that the key policy explicitly authorize the principal (or the role’s assumed-role session) when the key policy is the sole authorization mechanism. Updating the key policy to include the service role principal (or the assumed-role ARN) with kms:Decrypt directly resolves the missing permission.
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.
- ✓
Update the KMS key policy to allow kms:Decrypt for the service role principal (or the assumed-role principal identity that the KMS key evaluates).
Why this is correct
KMS authorization is controlled by the KMS key policy in addition to (not instead of) IAM identity policies. If the key policy does not allow the principal, KMS will deny kms:Decrypt even if the IAM policy allows it.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Add an IAM policy statement allowing s3:GetObject for the bucket that stores the encrypted data.
Why it's wrong here
S3 permissions determine whether the encrypted ciphertext can be retrieved. They do not grant cryptographic authorization to call kms:Decrypt on the KMS key.
- ✗
Enable a CloudFront distribution for the KMS key alias.
Why it's wrong here
CloudFront settings and distribution behavior do not affect KMS key policy evaluation for kms:Decrypt.
- ✗
Create a VPC gateway endpoint for KMS to route decryption requests privately.
Why it's wrong here
Private networking can affect connectivity, but it cannot replace authorization. Without key-policy permission, KMS will still deny kms:Decrypt with AccessDenied.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume IAM policies alone are sufficient for KMS authorization, but KMS key policies are resource-based and must explicitly include the principal (or the assumed-role session) when the key policy is the sole authorization mechanism.
Detailed technical explanation
How to think about this question
KMS key policies can be used as the sole authorization mechanism (default) or combined with IAM policies. When a key policy does not include the principal, even if the IAM policy allows the action, KMS denies the request because the key policy acts as a resource-based policy that must explicitly grant access. The assumed-role principal (e.g., arn:aws:sts::account-id:assumed-role/role-name/session-name) is often required instead of the role ARN, as KMS evaluates the principal identity of the caller, which is the assumed-role session.
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: Update the KMS key policy to allow kms:Decrypt for the service role principal (or the assumed-role principal identity that the KMS key evaluates). — The AccessDenied error occurs because the KMS key policy does not grant the service role (or its assumed-role principal) permission to call kms:Decrypt. Even if the IAM policy attached to the role allows kms:Decrypt, KMS requires that the key policy explicitly authorize the principal (or the role’s assumed-role session) when the key policy is the sole authorization mechanism. Updating the key policy to include the service role principal (or the assumed-role ARN) with kms:Decrypt directly resolves the missing permission.
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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