- A
The S3 bucket policy in Account A grants s3:GetObject to the IAM role in Account B, the KMS key policy in Account A grants kms:Decrypt to the IAM role in Account B, and the IAM role in Account B has a trust policy allowing the IAM user to assume it.
All three policies are required: the bucket policy for S3 access, the KMS key policy for decryption permissions, and the trust policy in Account B to allow the IAM user to assume the role.
- B
The S3 bucket policy in Account A grants s3:GetObject to the IAM role in Account B, and the IAM role in Account B has a trust policy allowing the IAM user to assume it. No KMS key policy is needed because the role can use the key via IAM policies.
Why wrong: For cross-account KMS operations, IAM policies alone are insufficient. The KMS key policy must explicitly grant access to principals from another account. IAM policies in Account A cannot grant access to principals in Account B.
- C
The S3 bucket policy in Account A grants s3:GetObject to the IAM user in Account B, and the IAM user's IAM policy grants s3:GetObject.
Why wrong: You cannot grant direct access to an IAM user in another account via a bucket policy; you must use a role. Also, the KMS key policy is missing.
- D
The S3 bucket uses SSE-C, so the developer must provide the encryption key in the request. No KMS key policy is needed.
Why wrong: The scenario specifies SSE-KMS, not SSE-C. For SSE-C, no key policy is needed, but cross-account bucket policy still required. However, SSE-C is not used here.
Quick Answer
The correct answer requires three distinct permissions: the S3 bucket policy in Account A must grant s3:GetObject to the IAM role in Account B, the KMS key policy in Account A must grant kms:Decrypt to that same role, and the IAM role in Account B must have a trust policy allowing the IAM user to assume it. This is necessary because cross-account S3 KMS encryption with a customer managed key (CMK) introduces a critical nuance: KMS key policies are resource-based and do not trust IAM policies from other accounts, so the external role must be explicitly listed in the key policy for decryption to succeed. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of the layered permission model—bucket policy, key policy, and role trust policy—and the common trap is assuming that an IAM policy in Account B alone can authorize KMS decryption. A reliable memory tip is “three locks for cross-account SSE-KMS: bucket, key, and trust.”
DVA-C02 Security Practice Question
This DVA-C02 practice question tests your understanding of security. 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 developer needs to grant read-only access to objects in an S3 bucket (in Account A) to an IAM role in Account B. The bucket uses server-side encryption with AWS KMS (SSE-KMS) using a customer managed key (CMK) in Account A. Which of the following is REQUIRED for the cross-account access to succeed?
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
The S3 bucket policy in Account A grants s3:GetObject to the IAM role in Account B, the KMS key policy in Account A grants kms:Decrypt to the IAM role in Account B, and the IAM role in Account B has a trust policy allowing the IAM user to assume it.
Option A is correct because cross-account access to an S3 bucket with SSE-KMS using a customer managed key requires three distinct permissions: the S3 bucket policy must grant s3:GetObject to the IAM role in Account B, the KMS key policy must grant kms:Decrypt to that same role (since KMS key policies are resource-based and do not trust IAM policies from other accounts), and the IAM role in Account B must have a trust policy that allows the IAM user to assume it. Without the KMS key policy explicitly allowing the external role, the decryption step will fail, even if the S3 bucket policy permits the read operation.
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.
- ✓
The S3 bucket policy in Account A grants s3:GetObject to the IAM role in Account B, the KMS key policy in Account A grants kms:Decrypt to the IAM role in Account B, and the IAM role in Account B has a trust policy allowing the IAM user to assume it.
Why this is correct
All three policies are required: the bucket policy for S3 access, the KMS key policy for decryption permissions, and the trust policy in Account B to allow the IAM user to assume the role.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The S3 bucket policy in Account A grants s3:GetObject to the IAM role in Account B, and the IAM role in Account B has a trust policy allowing the IAM user to assume it. No KMS key policy is needed because the role can use the key via IAM policies.
Why it's wrong here
For cross-account KMS operations, IAM policies alone are insufficient. The KMS key policy must explicitly grant access to principals from another account. IAM policies in Account A cannot grant access to principals in Account B.
- ✗
The S3 bucket policy in Account A grants s3:GetObject to the IAM user in Account B, and the IAM user's IAM policy grants s3:GetObject.
Why it's wrong here
You cannot grant direct access to an IAM user in another account via a bucket policy; you must use a role. Also, the KMS key policy is missing.
- ✗
The S3 bucket uses SSE-C, so the developer must provide the encryption key in the request. No KMS key policy is needed.
Why it's wrong here
The scenario specifies SSE-KMS, not SSE-C. For SSE-C, no key policy is needed, but cross-account bucket policy still required. However, SSE-C is not used here.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume IAM policies in the target account are sufficient for KMS operations, forgetting that KMS key policies are resource-based and must explicitly grant cross-account access, unlike S3 bucket policies which can reference external principals directly.
Trap categories for this question
Scenario analysis trap
The scenario specifies SSE-KMS, not SSE-C. For SSE-C, no key policy is needed, but cross-account bucket policy still required. However, SSE-C is not used here.
Detailed technical explanation
How to think about this question
Under the hood, when an S3 GET request is made against an SSE-KMS encrypted object, S3 calls KMS to decrypt the object's data key; this KMS Decrypt API call must be authorized by the KMS key policy, which is a resource-based policy that does not inherit cross-account trust from IAM. A real-world scenario is when a data lake in Account A needs to be queried by analytics workloads in Account B—without the KMS key policy explicitly listing the Account B role, the decryption fails with an AccessDeniedException, even though the S3 bucket policy allows the read.
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 DVA-C02 question test?
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The S3 bucket policy in Account A grants s3:GetObject to the IAM role in Account B, the KMS key policy in Account A grants kms:Decrypt to the IAM role in Account B, and the IAM role in Account B has a trust policy allowing the IAM user to assume it. — Option A is correct because cross-account access to an S3 bucket with SSE-KMS using a customer managed key requires three distinct permissions: the S3 bucket policy must grant s3:GetObject to the IAM role in Account B, the KMS key policy must grant kms:Decrypt to that same role (since KMS key policies are resource-based and do not trust IAM policies from other accounts), and the IAM role in Account B must have a trust policy that allows the IAM user to assume it. Without the KMS key policy explicitly allowing the external role, the decryption step will fail, even if the S3 bucket policy permits the read operation.
What should I do if I get this DVA-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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Last reviewed: Jun 11, 2026
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