- A
Update the KMS key policy to allow the partner role or account to use the key.
KMS evaluates the key policy before permitting use of a customer managed key. Cross-account use requires the key policy to trust the external principal or a grant to that principal.
- B
Enable automatic key rotation to solve the cross-account access requirement.
Why wrong: Key rotation improves cryptographic hygiene, but it does not grant permissions to another account. Access control is handled by policies or grants, not rotation settings.
- C
Attach IAM permissions in the partner account for kms:Encrypt, kms:Decrypt, and kms:GenerateDataKey on the CMK.
The partner role also needs IAM permission to call KMS actions against the key. Cross-account KMS access requires both an identity policy and a key policy or grant.
- D
Replace the CMK with the AWS managed key alias/aws/s3.
Why wrong: AWS managed keys are not designed for this kind of cross-account sharing model. They also do not give the same policy control as a customer managed KMS key.
- E
Export the KMS key material and share it with the partner account.
Why wrong: Exporting key material is not a normal or recommended pattern for KMS access. It undermines the service model and is unnecessary when key policy and IAM permissions are available.
Quick Answer
The answer is that you must attach IAM permissions in the partner account for kms:Encrypt, kms:Decrypt, and kms:GenerateDataKey on the CMK, and also update the KMS key policy in the central account to grant the partner account or its assumed role explicit access. This is required because cross-account KMS key access relies on a two-part authorization model: the key policy must allow the external principal, and that principal must have matching IAM permissions in their own account to invoke the cryptographic operations. On the SAA-C03 exam, this scenario tests your understanding that S3 bucket access alone does not imply KMS key access—a common trap is assuming the partner’s S3 role automatically inherits encryption permissions. The key policy acts as the resource-based gatekeeper, while the partner’s IAM policy provides the identity-based permission; both must align for the decrypt or encrypt call to succeed. Memory tip: think “Key Policy + IAM = Cross-Account Key Access.”
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. A key principle to apply: kMS key policies are the primary access control for CMKs.. 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 central security account stores encrypted log files in S3 using a customer managed AWS KMS key. A partner account already has S3 bucket access through an assumed role and now must also be able to encrypt and decrypt objects that use the same KMS key. Which two actions are required? 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
Update the KMS key policy to allow the partner role or account to use the key.
Option A is correct because the KMS key policy must explicitly grant the partner account or role permission to use the key for cryptographic operations. Without this cross-account policy statement, the key remains inaccessible to the partner account, even if the partner has S3 bucket access. This is a fundamental requirement for cross-account KMS key usage.
Key principle: KMS key policies are the primary access control for CMKs.
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 the partner role or account to use the key.
Why this is correct
KMS evaluates the key policy before permitting use of a customer managed key. Cross-account use requires the key policy to trust the external principal or a grant to that principal.
Related concept
KMS key policies are the primary access control for CMKs.
- ✗
Enable automatic key rotation to solve the cross-account access requirement.
Why it's wrong here
Key rotation improves cryptographic hygiene, but it does not grant permissions to another account. Access control is handled by policies or grants, not rotation settings.
- ✓
Attach IAM permissions in the partner account for kms:Encrypt, kms:Decrypt, and kms:GenerateDataKey on the CMK.
Why this is correct
The partner role also needs IAM permission to call KMS actions against the key. Cross-account KMS access requires both an identity policy and a key policy or grant.
Related concept
KMS key policies are the primary access control for CMKs.
- ✗
Replace the CMK with the AWS managed key alias/aws/s3.
Why it's wrong here
AWS managed keys are not designed for this kind of cross-account sharing model. They also do not give the same policy control as a customer managed KMS key.
- ✗
Export the KMS key material and share it with the partner account.
Why it's wrong here
Exporting key material is not a normal or recommended pattern for KMS access. It undermines the service model and is unnecessary when key policy and IAM permissions are available.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often forget that cross-account KMS access requires both a key policy update in the central account AND IAM permissions in the partner account, not just one of them.
Detailed technical explanation
How to think about this question
For cross-account KMS key usage, the key policy must include a statement that grants the partner account's root user or assumed role permission for kms:Encrypt, kms:Decrypt, and kms:GenerateDataKey. Additionally, the partner account must attach an IAM policy to its role granting the same permissions. This two-step process is required because KMS uses a combination of key policies and IAM policies for cross-account access, unlike single-account scenarios where IAM alone suffices.
KKey Concepts to Remember
- KMS key policies are the primary access control for CMKs.
- Cross-account KMS access requires both key policy and IAM policy permissions.
- The key policy must explicitly trust the external account or principal.
- KMS key policies are evaluated before IAM policies for CMK access.
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
KMS key policies are the primary access control for CMKs.
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 — KMS key policies are the primary access control for CMKs..
What is the correct answer to this question?
The correct answer is: Update the KMS key policy to allow the partner role or account to use the key. — Option A is correct because the KMS key policy must explicitly grant the partner account or role permission to use the key for cryptographic operations. Without this cross-account policy statement, the key remains inaccessible to the partner account, even if the partner has S3 bucket access. This is a fundamental requirement for cross-account KMS key usage.
What should I do if I get this SAA-C03 question wrong?
Review kMS key policies are the primary access control for CMKs., then practise related SAA-C03 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
KMS key policies are the primary access control for CMKs.
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Same concept, more angles
1 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. A central security account stores encrypted log files in S3 using a customer managed AWS KMS key. A partner account already has S3 bucket access through an assumed role and now must also be able to encrypt and decrypt objects that use the same KMS key. Which two actions are required? Select two.
medium- ✓ A.Update the KMS key policy to allow the partner role or account to use the key.
- B.Enable automatic key rotation to solve the cross-account access requirement.
- ✓ C.Attach IAM permissions in the partner account for kms:Encrypt, kms:Decrypt, and kms:GenerateDataKey on the CMK.
- D.Replace the CMK with the AWS managed key alias/aws/s3.
- E.Export the KMS key material and share it with the partner account.
Why A: Option A is correct because the KMS key policy must explicitly grant the partner account or its assumed role permission to use the key for cryptographic operations. Without this cross-account policy statement, the partner account cannot access the key even if it has IAM permissions, as KMS key policies are the primary access control mechanism for cross-account usage.
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Last reviewed: Jun 11, 2026
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