Quick Answer
The answer is SSE-C, Server-Side Encryption with Customer-Provided Keys, because it uniquely allows you to supply your own encryption keys from AWS CloudHSM on every PUT request, ensuring that S3 never stores or independently accesses the keys. With SSE-C, the customer retains full control over the key material outside of AWS, and S3 can only decrypt objects when the correct key is explicitly provided per request—meeting the requirement that the bucket cannot access keys without explicit permission. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of the critical distinction between key ownership and key storage: SSE-KMS stores keys in AWS, SSE-S3 manages them entirely, but only SSE-C forces the customer to supply keys from an external source like CloudHSM. A common trap is confusing SSE-C with SSE-KMS using a custom key store backed by CloudHSM; remember that SSE-C requires you to pass the key with every API call, while KMS still stores the key metadata in AWS. Memory tip: SSE-C stands for “Customer-Controlled”—you bring the key, you keep the control.
This SAP-C02 practice question tests your understanding of design for new solutions. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 financial services company needs to store sensitive customer data in Amazon S3 with encryption at rest. They require that the encryption keys be stored in AWS CloudHSM and that the S3 bucket must not be able to access the keys without explicit permission. Which S3 encryption option should they use?
SSE-S3
Why wrong: Uses AWS-managed keys, not CloudHSM.
SSE-C
Allows customer to provide keys stored in CloudHSM.
Client-side encryption
Why wrong: Encryption is done before upload, not S3-managed.
SSE-KMS
Why wrong: Uses KMS, not CloudHSM.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
SSE-C
SSE-C (Server-Side Encryption with Customer-Provided Keys) is correct because it allows the customer to supply their own encryption keys, which can be stored in AWS CloudHSM, and S3 will use those keys to encrypt data at rest. With SSE-C, the customer manages the keys outside of AWS, and S3 cannot access the keys without explicit permission because the keys are provided per request and not stored by AWS. This meets the requirement of storing keys in CloudHSM and ensuring S3 has no independent access to them.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
SSE-S3
Why it's wrong here
Uses AWS-managed keys, not CloudHSM.
SSE-C
Why this is correct
Allows customer to provide keys stored in CloudHSM.
Related concept
Read the scenario before looking for a memorised answer.
Client-side encryption
Why it's wrong here
Encryption is done before upload, not S3-managed.
SSE-KMS
Why it's wrong here
Uses KMS, not CloudHSM.
Common exam traps
The trap here is that candidates often choose SSE-KMS assuming it supports CloudHSM via a custom key store, but SSE-KMS still allows S3 to access the key through KMS policies without requiring the key to be provided per request, which does not meet the 'explicit permission per access' requirement as strictly as SSE-C does.
Detailed technical explanation
SSE-C works by requiring the client to include the encryption key (a 256-bit AES key) in each request to S3 via the `x-amz-server-side-encryption-customer-key` header; S3 uses this key to encrypt/decrypt the object but does not store the key, ensuring that without the key, S3 cannot access the data. This contrasts with SSE-KMS, where the key is stored in KMS and S3 can call KMS on behalf of the principal, but the key material is not directly provided per request. In practice, SSE-C is ideal for regulatory environments like PCI-DSS where key material must be held exclusively by the customer in a dedicated HSM, such as CloudHSM, and never persisted by the cloud provider.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
Design for New Solutions — This question tests Design for New Solutions — Read the scenario before looking for a memorised answer..
The correct answer is: SSE-C — SSE-C (Server-Side Encryption with Customer-Provided Keys) is correct because it allows the customer to supply their own encryption keys, which can be stored in AWS CloudHSM, and S3 will use those keys to encrypt data at rest. With SSE-C, the customer manages the keys outside of AWS, and S3 cannot access the keys without explicit permission because the keys are provided per request and not stored by AWS. This meets the requirement of storing keys in CloudHSM and ensuring S3 has no independent access to them.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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