The answer is to configure the S3 bucket policy to deny uploads that do not use the required KMS key, combined with a customer-managed key (CMK) policy that grants cross-account permissions. This works because the S3 bucket policy enforces encryption at rest by rejecting any `PutObject` request that lacks the `x-amz-server-side-encryption-aws-kms-key-id` header matching your CMK, while the key policy explicitly allows consumer accounts to perform `kms:Decrypt` and `kms:GenerateDataKey`. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of the interaction between resource-based policies (S3 bucket) and key policies (KMS) for cross-account encryption—a common trap is assuming IAM policies alone suffice, but KMS key policies must explicitly list external principals. A memory tip: “Bucket denies, key allows—cross-account encryption follows.”
SAP-C02 Practice Question: Design Solutions for Organizational Complexity
This SAP-C02 practice question tests your understanding of design solutions for organizational complexity. 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 is implementing a data lake on AWS using Amazon S3 as the storage layer. The data lake must support multiple consumer accounts within the organization. The security team requires that data is encrypted at rest using AWS KMS with customer-managed keys (CMKs) and that access to the keys is strictly controlled. Which THREE steps should be taken to meet these requirements?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a customer-managed KMS key with a key policy that allows the consumer accounts to use the key.
Option A is correct because creating a customer-managed KMS key (CMK) with a key policy that explicitly grants the consumer accounts permission to use the key (e.g., via the `kms:Decrypt` and `kms:GenerateDataKey` actions) is required for cross-account encryption. This ensures that the S3 bucket can encrypt objects with the CMK, and consumer accounts can decrypt them using their own IAM permissions, meeting the security team's requirement for strict key control.
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 a customer-managed KMS key with a key policy that allows the consumer accounts to use the key.
Why this is correct
Allows cross-account decryption.
Related concept
Read the scenario before looking for a memorised answer.
✓
Grant cross-account access to the S3 bucket using bucket policies.
Why this is correct
Allows consumer accounts to access the data.
Related concept
Read the scenario before looking for a memorised answer.
✓
Configure the S3 bucket policy to deny uploads that do not use the required KMS key.
Why this is correct
Enforces encryption at upload time.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use an SCP to require that all S3 buckets use server-side encryption with KMS.
Why it's wrong here
SCPs cannot enforce encryption settings on existing buckets.
✗
Create IAM roles in each consumer account that grant access to the KMS key.
Why it's wrong here
Not necessary; key policy can grant access directly.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse SCPs with resource-based policies, thinking an SCP can enforce cross-account encryption access, when in reality SCPs only set permission boundaries and cannot grant the specific KMS key usage permissions required for cross-account decryption.
Detailed technical explanation
How to think about this question
Under the hood, AWS KMS uses a key policy as a resource-based policy that defines who can use the CMK across accounts. For cross-account access, the key policy must include a statement granting the root ARN of the consumer account (e.g., `arn:aws:iam::CONSUMER_ACCOUNT_ID:root`) the necessary KMS actions, and the consumer account must then delegate those permissions to its IAM users or roles via IAM policies. Additionally, the S3 bucket policy must allow the `s3:PutObject` action with a condition that `s3:x-amz-server-side-encryption-aws-kms-key-id` matches the specific CMK ARN to enforce encryption with that key.
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.
Design Solutions for Organizational Complexity — This question tests Design Solutions for Organizational Complexity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a customer-managed KMS key with a key policy that allows the consumer accounts to use the key. — Option A is correct because creating a customer-managed KMS key (CMK) with a key policy that explicitly grants the consumer accounts permission to use the key (e.g., via the `kms:Decrypt` and `kms:GenerateDataKey` actions) is required for cross-account encryption. This ensures that the S3 bucket can encrypt objects with the CMK, and consumer accounts can decrypt them using their own IAM permissions, meeting the security team's requirement for strict key control.
What should I do if I get this SAP-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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