DEA-C01 Data Security and Governance Practice Question
A data engineer is setting up a data pipeline that ingests streaming data from Amazon Kinesis Data Streams into an S3 data lake using Amazon Kinesis Data Firehose. The data contains personally identifiable information (PII). The security team requires that all data be encrypted at rest in S3 using an AWS KMS customer managed key (CMK) that is specific to the application. Additionally, the data must be encrypted in transit between all services. The engineer creates the KMS key and configures Firehose to use server-side encryption with the key for the S3 destination. However, Firehose delivery fails with an error indicating that the KMS key is not accessible. What is the most likely cause?
⚠ Common exam trap
DEA-C01 often tests the two-layer KMS authorization model — candidates focus on IAM roles or S3 bucket policies and forget that the KMS key policy must explicitly grant the AWS service principal access.
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 KMS key policy does not grant the firehose.amazonaws.com service principal the required permissions.
When Firehose writes to S3 using SSE-KMS with a customer managed key, the Firehose service principal (firehose.amazonaws.com) must be granted kms:GenerateDataKey and kms:Decrypt in the KMS key policy. Without that grant, Firehose cannot obtain the data key to encrypt objects, and delivery fails with an access-denied error referencing the KMS key. The key policy is the resource-based control that authorizes the service principal.
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 KMS key policy does not grant the firehose.amazonaws.com service principal the required permissions.
Why this is correct
Firehose assumes the `firehose.amazonaws.com` service principal to call KMS GenerateDataKey and Decrypt on your behalf, so the CMK's key policy must explicitly grant that principal those actions. Without this grant, the key is inaccessible and delivery fails, even though the IAM role used for S3 access is correctly configured.
- ✗
The Kinesis data stream is not encrypted at rest.
Why it's wrong here
Firehose reads from the stream using its own IAM role and does not require the source stream to be KMS-encrypted; stream encryption state cannot cause a destination key access error. It is tempting because encryption is mentioned throughout, and encrypting the stream would be correct for protecting records at rest in Kinesis.
- ✗
The Firehose delivery stream is not in the same region as the KMS key.
Why it's wrong here
Firehose and a KMS key must be in the same region, but the reported error is key access, not region mismatch, so this does not explain the failure. It is tempting because cross-region KMS use is a real constraint, and it would be correct if the key genuinely sat in another region.
- ✗
The S3 bucket policy does not grant the Firehose delivery stream access to write objects.
Why it's wrong here
Firehose's KMS access depends on the IAM role's key policy and KMS grants, not S3 write permissions; an S3 bucket policy denial produces an access-denied write error instead. Bucket policies are tempting because they commonly gate Firehose delivery, and would be correct if the failure were S3 authorisation rather than key access.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
This DEA-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 DEA-C01 exam.