The correct answer is to modify the KMS key policy to include a condition that allows kms:Decrypt only if the SAML assertion contains the specific attribute. This works because KMS key policies support condition keys like `saml:sub` or custom SAML attributes mapped to IAM role session tags via `aws:PrincipalTag`, enabling attribute-based access control directly at the key level. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of how to enforce fine-grained decryption restrictions using SAML federated identities, often appearing as a trap where candidates mistakenly apply the condition to an S3 bucket policy or IAM policy instead of the key policy itself. A common memory tip is to remember that KMS key policies are the only place you can evaluate SAML attributes for decryption—S3 and IAM policies cannot inspect the contents of a SAML assertion. Think of it as "key policy, not bucket policy" for SAML-driven decryption gates.
DOP-C02 Security and Compliance Practice Question
This DOP-C02 practice question tests your understanding of security and compliance. 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.
A company uses AWS Key Management Service (KMS) to encrypt data at rest in Amazon S3. The security team wants to ensure that only users with a specific attribute in their SAML assertion can decrypt the data. Which KMS key policy should be used?
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 to include a condition that allows kms:Decrypt only if the SAML assertion contains the specific attribute.
Option B is correct because KMS key policies can use the `kms:ViaService` or `kms:CallerPrincipal` conditions, but more importantly, they can reference SAML-based attributes using the `aws:PrincipalTag` or `saml:sub` conditions. By adding a condition in the KMS key policy that checks for a specific SAML assertion attribute (e.g., `saml:sub` or a custom SAML attribute mapped to an IAM role session tag), only users whose SAML assertion includes that attribute will be allowed to call `kms:Decrypt`. This directly enforces the security team's requirement at the key level, independent of S3 bucket policies or IAM policies.
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.
✗
Create an S3 bucket policy that denies kms:Decrypt unless the request includes a specific tag.
Why it's wrong here
S3 bucket policies cannot deny KMS actions.
✓
Modify the KMS key policy to include a condition that allows kms:Decrypt only if the SAML assertion contains the specific attribute.
Why this is correct
KMS key policies can use conditions based on SAML attributes to control decryption.
Related concept
Read the scenario before looking for a memorised answer.
✗
Attach a resource-based policy to the S3 bucket that allows decryption only for users with the specific attribute.
Why it's wrong here
S3 bucket policies do not control KMS decryption permissions.
✗
Use an IAM policy that grants kms:Decrypt only if the user has the specific attribute.
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse S3 bucket policies with KMS key policies, thinking they can control KMS decryption via S3 policies, when in reality KMS key policies are the only way to enforce conditions on the `kms:Decrypt` action at the key level.
Detailed technical explanation
How to think about this question
KMS key policies support conditions like `aws:SourceIdentity` or `saml:sub` when the principal is a SAML-federated role. Under the hood, when a user assumes a role via SAML federation, AWS STS creates temporary credentials with attributes from the SAML assertion, which can be referenced in KMS key policies using the `saml:sub` or custom attribute keys. This allows fine-grained access control at the key level, ensuring that even if an IAM role has broad KMS permissions, the key policy can restrict decryption to only those federated users with the required SAML attribute.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security and Compliance — This question tests Security and Compliance — 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 to include a condition that allows kms:Decrypt only if the SAML assertion contains the specific attribute. — Option B is correct because KMS key policies can use the `kms:ViaService` or `kms:CallerPrincipal` conditions, but more importantly, they can reference SAML-based attributes using the `aws:PrincipalTag` or `saml:sub` conditions. By adding a condition in the KMS key policy that checks for a specific SAML assertion attribute (e.g., `saml:sub` or a custom SAML attribute mapped to an IAM role session tag), only users whose SAML assertion includes that attribute will be allowed to call `kms:Decrypt`. This directly enforces the security team's requirement at the key level, independent of S3 bucket policies or IAM policies.
What should I do if I get this DOP-C02 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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Question Discussion
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