MLS-C01 Data Engineering Practice Question
A company is building a data lake on Amazon S3 and wants to ensure that data is encrypted at rest using AWS KMS. Which TWO actions are required to achieve this? (Choose TWO.)
⚠ Common exam trap
Many candidates confuse 'encryption at rest' with 'encryption in transit' or 'enforcing encryption via bucket policies,' and may select options like C or D, which address different security controls, instead of focusing on the specific mechanism (SSE-KMS) and the necessary KMS key policy configuration.
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
✓
Configure the KMS key policy to allow the S3 service to use the key
AWS KMS uses key policies to control access to the KMS key. For S3 to use a KMS key for server-side encryption (SSE-KMS), the key policy must grant the S3 service principal (or the bucket owner's account) the necessary permissions, such as kms:Encrypt and kms:Decrypt. Without this policy, S3 cannot access the key to encrypt or decrypt objects at rest. Option B is correct because enabling default encryption on the S3 bucket with SSE-KMS ensures that all objects uploaded to the bucket are automatically encrypted using the specified KMS key, meeting the requirement for encryption at rest.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure the KMS key policy to allow the S3 service to use the key
Why this is correct
The key policy must grant the S3 service principal permission to encrypt/decrypt.
- ✓
Enable default encryption on the S3 bucket with SSE-KMS
Why this is correct
Default encryption ensures all objects are encrypted with KMS.
- ✗
Add a bucket policy that denies PutObject without encryption
Why it's wrong here
This enforces encryption but does not set up the encryption itself.
- ✗
Enable encryption in transit using HTTPS for all S3 API calls
Why it's wrong here
Encryption in transit is separate from encryption at rest.
- ✗
Use client-side encryption on all data before uploading
Why it's wrong here
Client-side encryption is an alternative, not required if using server-side encryption.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This MLS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the MLS-C01 exam.