- A
Add an SCP that grants the role additional permissions for KMS usage.
Why wrong: Service control policies cannot grant permissions. SCPs only set the maximum permissions that identities in an account or OU can use; they never add allow permissions.
- B
Add kms:Decrypt permission in the role's IAM policy for the KMS key.
The caller needs an identity-based permission that allows kms:Decrypt on the specific CMK used to encrypt the S3 object. Without that allow statement, KMS denies the decrypt request even if S3 access is permitted.
- C
Update the KMS key policy in Account A to allow the role from Account B to use Decrypt.
For cross-account SSE-KMS access, the CMK policy in the owning account must trust the external principal or an authorized account path. KMS evaluates both the identity policy and the key policy, so both must allow the operation.
- D
Grant the role read access with an S3 bucket ACL.
Why wrong: An ACL can affect S3 object authorization, but it does not grant permission to use the KMS key. The failure is at the decrypt step, so changing the ACL alone does not resolve the access denied error.
- E
Enable S3 Transfer Acceleration on the bucket.
Why wrong: Transfer Acceleration only changes the network path for object transfers. It does not change IAM or KMS authorization and therefore cannot fix a missing decrypt permission.
Quick Answer
The answer is to update the KMS key policy in Account A and add a kms:Decrypt permission to the IAM role in Account B. This is required because cross-account SSE-KMS access to S3 demands a two-part authorization: the IAM policy of the consuming role must explicitly allow the kms:Decrypt action, and the customer managed key’s key policy in the owning account must grant that same role permission to call Decrypt. Without both, the role may have s3:GetObject but will fail with AccessDenied on decrypt, as the S3 service cannot delegate decryption across accounts using only the bucket policy. On the SAA-C03 exam, this scenario tests your understanding that customer managed KMS keys are regional and require explicit cross-account key policy grants, unlike AWS managed keys which cannot be shared. A common trap is assuming the bucket policy alone suffices or that the key policy is optional. Memory tip: “Key policy for the key owner, IAM policy for the caller — both must say Decrypt.”
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 reads objects from an Amazon S3 bucket in Account A. The bucket uses SSE-KMS with a customer managed key in Account A. The role in Account B already has s3:GetObject, but downloads fail with AccessDenied on decrypt. Which two changes are required for the role to read the object successfully? Select two.
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
Add kms:Decrypt permission in the role's IAM policy for the KMS key.
Option B is correct because the role in Account B needs explicit kms:Decrypt permission in its IAM policy to use the KMS key for decrypting the S3 objects. Option C is correct because the KMS key policy in Account A must grant the role from Account B permission to call kms:Decrypt, as the key is customer managed and cross-account access requires both the key policy and the IAM policy to allow the action.
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 an SCP that grants the role additional permissions for KMS usage.
Why it's wrong here
Service control policies cannot grant permissions. SCPs only set the maximum permissions that identities in an account or OU can use; they never add allow permissions.
- ✓
Add kms:Decrypt permission in the role's IAM policy for the KMS key.
Why this is correct
The caller needs an identity-based permission that allows kms:Decrypt on the specific CMK used to encrypt the S3 object. Without that allow statement, KMS denies the decrypt request even if S3 access is permitted.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Update the KMS key policy in Account A to allow the role from Account B to use Decrypt.
Why this is correct
For cross-account SSE-KMS access, the CMK policy in the owning account must trust the external principal or an authorized account path. KMS evaluates both the identity policy and the key policy, so both must allow the operation.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Grant the role read access with an S3 bucket ACL.
Why it's wrong here
An ACL can affect S3 object authorization, but it does not grant permission to use the KMS key. The failure is at the decrypt step, so changing the ACL alone does not resolve the access denied error.
- ✗
Enable S3 Transfer Acceleration on the bucket.
Why it's wrong here
Transfer Acceleration only changes the network path for object transfers. It does not change IAM or KMS authorization and therefore cannot fix a missing decrypt permission.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think only the IAM policy (Option B) is needed, forgetting that cross-account KMS access requires the key policy (Option C) to explicitly grant the external role decrypt permission, as IAM policies alone are insufficient for resource-based policies like KMS key policies.
Detailed technical explanation
How to think about this question
When SSE-KMS is used, S3 calls KMS to decrypt the object key (data key) before returning the object. For cross-account access, the KMS key policy must explicitly allow the external IAM role to call kms:Decrypt, and the role must have the corresponding IAM permission. Without both, the decrypt call fails with AccessDenied even if s3:GetObject is allowed. The key policy acts as a resource-based policy that must trust the external principal.
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: Add kms:Decrypt permission in the role's IAM policy for the KMS key. — Option B is correct because the role in Account B needs explicit kms:Decrypt permission in its IAM policy to use the KMS key for decrypting the S3 objects. Option C is correct because the KMS key policy in Account A must grant the role from Account B permission to call kms:Decrypt, as the key is customer managed and cross-account access requires both the key policy and the IAM policy to allow the action.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
4 more ways this is tested on SAA-C03
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Based on the exhibit, an application role in Account B can reach an S3 bucket in Account A, but reads fail with AccessDenied on KMS. The bucket objects use SSE-KMS with a customer managed key in Account A. What change is required so the application can decrypt the objects while keeping the access restricted?
hard- ✓ A.Add the Account B role ARN to the KMS key policy with kms:Decrypt and kms:DescribeKey permissions, scoped to S3 usage in us-east-1.
- B.Add s3:GetEncryptionConfiguration to the Account B IAM policy so S3 can use the customer managed key on reads.
- C.Change the bucket to SSE-S3 because SSE-S3 always allows cross-account reads without any KMS policy changes.
- D.Add the Account B role to the bucket ACL with FULL_CONTROL so S3 can bypass KMS on behalf of the reader.
Why A: Option A is correct because when using SSE-KMS with a customer managed key, cross-account access requires the KMS key policy to explicitly grant the external IAM role (from Account B) the kms:Decrypt and kms:DescribeKey permissions. Without these, S3 can retrieve the encrypted object, but KMS will deny the decryption request, resulting in an AccessDenied error. Scoping the policy to S3 usage in us-east-1 follows the principle of least privilege while enabling the necessary decryption.
Variation 2. 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?
medium- 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.
- B.Update the IAM role in Account B to use the s3:GetObject permission only, and rely on S3 to authorize KMS decrypt automatically.
- ✓ 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).
- D.Switch the S3 bucket encryption from SSE-KMS to SSE-S3, keeping all existing IAM and KMS configuration unchanged.
Why C: 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.
Variation 3. 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?
easy- A.Add kms:Decrypt only to the Account B role’s IAM policy, without changing the customer-managed KMS key policy in Account A.
- B.Update the Account A S3 bucket policy to grant kms:Decrypt to Account B.
- ✓ C.Update the customer-managed KMS key policy in Account A to allow kms:Decrypt for the specific Account B role principal.
- D.Enable KMS key rotation, which automatically allows cross-account decrypt permissions.
Why C: 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.
Variation 4. Account B has an IAM role that includes kms:Decrypt for a specific KMS key ARN in account A. However, when the role tries to read an S3 object encrypted with that CMK, the application fails with AccessDenied: not authorized to perform kms:Decrypt. CloudTrail shows the KMS API call is denied by key policy. What is the most secure and correct fix?
medium- A.Update the IAM role in account B to include kms:Encrypt and kms:GenerateDataKey; then kms:Decrypt will start working automatically.
- ✓ B.Update the KMS key policy in account A to allow the account B role principal to use kms:Decrypt on the key.
- C.Disable key policy for the CMK by switching to S3-managed encryption, because KMS key policies are always enforced regardless of grants.
- D.Create an SCP in account A that allows kms:Decrypt for all accounts, avoiding changes to the key policy.
Why B: Option B is correct because cross-account access to a customer managed KMS key (CMK) requires the key policy to explicitly grant the external IAM role principal the necessary permissions (e.g., kms:Decrypt). Even if the IAM role in Account B has an IAM policy allowing kms:Decrypt, the KMS key policy in Account A acts as a resource-based policy that must also allow the action; without this, the request is denied by the key policy, as shown in CloudTrail.
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Last reviewed: Jun 11, 2026
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