DEA-C01 Data Store Management Practice Question

Exhibit

Refer to the exhibit.

{
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "kms:Decrypt",
        "kms:GenerateDataKey"
      ],
      "Resource": "arn:aws:kms:us-east-1:123456789012:key/abc123"
    },
    {
      "Effect": "Deny",
      "Action": "kms:Decrypt",
      "Resource": "*",
      "Condition": {
        "StringNotEquals": {
          "aws:SourceAccount": "123456789012"
        }
      }
    }
  ]
}

A data engineer is troubleshooting an access denied error when an AWS Lambda function tries to decrypt an object encrypted with the KMS key 'abc123'. The Lambda function's execution role has the above policy attached. What is the likely cause of the error?

⚠ Common exam trap

Candidates often assume IAM permissions alone are sufficient for KMS operations, overlooking that KMS key policies must explicitly grant access to the IAM role, which is a common source of access denied errors in cross-account or cross-service scenarios.

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 Lambda role decrypt permission

The error occurs because KMS requires both the IAM policy and the key policy to grant the necessary permissions. While the IAM policy attached to the Lambda execution role includes kms:Decrypt, the KMS key policy for 'abc123' does not explicitly grant the Lambda role permission to call kms:Decrypt. Since KMS key policies act as a resource-based policy, they must allow the principal (the Lambda role) to perform the action; otherwise, the request is denied even if the IAM policy allows it.

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 Deny statement blocks all decrypt requests
Why it's wrong here
The Deny only applies when source account is not 123456789012; same account, so not denied.
✗
The Lambda function does not have permission to call kms:GenerateDataKey
Why it's wrong here
The policy allows GenerateDataKey on the key.
✓
The KMS key policy does not grant the Lambda role decrypt permission
Why this is correct
Key policies must also grant access; IAM alone may not be sufficient.
✗
The IAM policy does not include kms:Decrypt permission
Why it's wrong here
The policy includes kms:Decrypt on the specific key.

Quick reference

Cloud Service Model Comparison

Model	You Manage	Provider Manages	Examples
IaaS	OS, runtime, apps, data	Hardware, hypervisor, networking	EC2, Azure VMs, GCP Compute Engine
PaaS	Apps and data	OS, runtime, middleware, hardware	Elastic Beanstalk, Azure App Service
SaaS	Data and settings only	Everything else	Microsoft 365, Salesforce, Workday
FaaS / Serverless	Function code only	Infra, scaling, runtime	Lambda, Azure Functions, Cloud Run
CaaS	Containers and apps	Kubernetes, OS, hardware	EKS, AKS, GKE

Go deeper

DEA-C01 Data Store Management Practice Question

Exhibit

Why each option matters

Option-by-option breakdown

Cloud Service Model Comparison

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