AWS DVA-C02 Drill: S3 Encryption in Transit - Bucket Policy vs. Infrastructure Controls

Jeff’s Note

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Jeff’s Note

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“Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Lead Developer.”

“For DVA-C02 candidates, the confusion often lies in mixing up encryption at rest (SSE-KMS) with encryption in transit (TLS/HTTPS). In production, this is about knowing exactly which S3 API condition keys enforce protocol-level requirements versus storage-level encryption. Let’s drill down.”

The Certification Drill (Simulated Question)

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Scenario

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Your team at CloudVault Analytics operates a data processing pipeline where EC2-based microservices continuously upload analytics logs to an S3 bucket. The compliance team has mandated that all data transfers to S3 must occur over encrypted channels to meet industry security standards. As the lead developer, you need to implement a solution that programmatically enforces this requirement at the bucket level.

The Requirement:

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Ensure that all traffic between the EC2 instances and the S3 bucket is encrypted in transit, with the enforcement mechanism preventing any unencrypted connections.

The Options

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• A) Install TLS certificates on the EC2 instances and configure the application to use HTTPS endpoints
• B) Create a VPC endpoint for S3 with private connectivity
• C) Configure the S3 bucket with server-side encryption using AWS KMS managed keys (SSE-KMS)
• D) Create an S3 bucket policy that denies traffic when the value for the aws:SecureTransport condition key is false

Correct Answer

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D.

Quick Insight: The Developer’s Enforcement Imperative

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For DVA-C02: This tests your understanding of IAM policy condition keys and the distinction between transport-layer encryption (HTTPS/TLS) and storage-layer encryption (SSE-*). The aws:SecureTransport condition is the programmatic enforcement mechanism that rejects non-HTTPS API calls at the bucket policy level—no application changes required.

Content Locked: The Expert Analysis

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You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?

The Expert’s Analysis

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Correct Answer

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Option D

The Winning Logic

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Option D is correct because it leverages the aws:SecureTransport IAM condition key within an S3 bucket policy to enforce encryption in transit at the bucket access control layer.

Why this is the developer’s choice:

• Declarative Enforcement: The bucket policy acts as a gatekeeper—any API request (PutObject, GetObject, etc.) made over HTTP (not HTTPS) is automatically denied with a 403 Forbidden response.
• No Application Code Changes: Unlike Option A, you don’t need to modify SDK configurations or install certificates. The AWS SDKs use HTTPS by default, so compliant applications work immediately.
• Global Bucket-Level Control: The policy applies to all principals attempting to access the bucket, making it a centralized security control rather than relying on individual EC2 instance configurations.
• DVA-C02 Focus: The exam tests your knowledge of S3 bucket policy syntax and IAM condition operators—specifically how to use Boolean conditions to enforce protocol requirements.

Key API behavior: When aws:SecureTransport evaluates to false (HTTP request), the explicit Deny statement in the bucket policy takes precedence over any Allow statements, blocking the request before data transmission occurs.

The Trap (Distractor Analysis):

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• Why not Option A? Installing certificates on EC2 instances doesn’t enforce anything—it merely enables HTTPS capability. A misconfigured application could still make HTTP requests. This is a permissive approach, not an enforcement mechanism. Additionally, AWS SDK clients use HTTPS by default without requiring certificate installation.

• Why not Option B? A VPC endpoint provides private connectivity and can reduce data transfer costs, but it does not enforce encryption in transit. Traffic through a VPC endpoint can still theoretically use HTTP if the application is misconfigured. VPC endpoints address network routing, not protocol enforcement.

• Why not Option C? SSE-KMS is server-side encryption at rest—it encrypts data after it arrives at S3. This has zero impact on the transport layer (HTTP vs. HTTPS). This is the classic exam trap: confusing encryption at rest with encryption in transit. The data could be transmitted over unencrypted HTTP and then encrypted at rest, which fails the compliance requirement.

The Technical Blueprint

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Developer Implementation: S3 Bucket Policy with aws:SecureTransport

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "DenyInsecureTransport",
      "Effect": "Deny",
      "Principal": "*",
      "Action": "s3:*",
      "Resource": [
        "arn:aws:s3:::cloudvault-analytics-logs",
        "arn:aws:s3:::cloudvault-analytics-logs/*"
      ],
      "Condition": {
        "Bool": {
          "aws:SecureTransport": "false"
        }
      }
    }
  ]
}

CLI command to apply the policy:

aws s3api put-bucket-policy \
  --bucket cloudvault-analytics-logs \
  --policy file://deny-insecure-transport-policy.json

Testing the enforcement:

# This will succeed (HTTPS by default in AWS CLI)
aws s3 cp test-file.txt s3://cloudvault-analytics-logs/

# Force HTTP using s3api (will fail with 403)
aws s3api put-object \
  --bucket cloudvault-analytics-logs \
  --key test-file.txt \
  --body test-file.txt \
  --endpoint-url http://s3.amazonaws.com
# Error: An error occurred (AccessDenied) when calling the PutObject operation

The Comparative Analysis

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Real-World Application (Practitioner Insight)

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Exam Rule

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“For the DVA-C02 exam, when you see ’enforce encryption in transit’ or ‘all traffic must be encrypted’, immediately look for a solution using the aws:SecureTransport condition key in a bucket policy. This is the only option that programmatically blocks unencrypted connections.”

Real World

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“In production environments, we typically implement a defense-in-depth strategy: deploy the aws:SecureTransport bucket policy as the enforcement layer, AND use VPC endpoints (Option B) for cost optimization and network isolation, AND enable SSE-KMS (Option C) for encryption at rest. The exam tests your ability to isolate the specific mechanism that addresses transport-layer requirements—but real architectures layer multiple controls.”

Bonus developer insight: Always test bucket policies in a non-production environment first. An overly restrictive Deny statement can lock out even the root account if conditions aren’t properly scoped. Use aws:SourceIp or aws:PrincipalOrgID conditions to whitelist trusted sources while still enforcing HTTPS.

Stop Guessing, Start Mastering

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Disclaimer

This is a study note based on simulated scenarios for the AWS DVA-C02 exam. All company names and scenarios are fictional and created for educational purposes. Always refer to official AWS documentation and practice with AWS accounts for hands-on experience.