Getting Started with Envelope Encryption in AWS KMS

Introduction

Envelope encryption is a method that uses two keys for encryption: a data key that encrypts the data and a master key that encrypts the data key. This approach is particularly useful for securing large amounts of data. In this post, we'll walk through the basics of getting started with envelope encryption in AWS KMS, including steps for encryption and decryption.

Understanding the Basics

Before diving into the implementation, let's understand two key components:

• KMS Keys: Previously known as Customer Master Keys (CMKs), these are the primary keys managed within AWS KMS, used to encrypt and decrypt data keys. It's not used to encrypt our data directly.
• Data Key: A key used to encrypt and decrypt our data directly. AWS KMS generates this key, and it can be used locally in your application.

Implementation Steps

Step 1: Setting Up KMS Key (Previously CMK)

First, we need a KMS key in AWS KMS. We can use an existing KMS Key or create a new one specifically for our application.

1. Log in to the AWS Management Console.
2. Navigate to the KMS dashboard.
3. Choose “Create a key” and follow the on-screen instructions to set up our KMS Key.
4. Note down the KMS Key ID or ARN as we will need it for encrypting and decrypting our data keys.

Step 2: Generate a Data Key

1. Use the GenerateDataKey API, specifying your KMS Key and the key spec (e.g., AES_256).
2. AWS KMS returns two versions of the data key: the plaintext data key and the encrypted data key. Store the encrypted data key securely with our encrypted data.

Step 3: Encrypting Data Using Envelope Encryption

1. Use the plaintext data key to encrypt our data locally using a cryptographic library that supports our chosen algorithm (e.g., AES).
2. Securely erase the plaintext data key from memory after encryption.
3. Store our encrypted data alongside the encrypted data key.

Step 3: Decrypting Your Data

When we need to access our encrypted data, we must decrypt the data key using AWS KMS and then use it to decrypt our data.

1. Retrieve the encrypted data key stored with our encrypted data.
2. Call the Decrypt API with the encrypted data key. AWS KMS returns the plaintext data key.
3. Use the plaintext data key to decrypt our data locally.
4. Securely erase the plaintext data key from memory after decryption.

Best Practices

• Security: Never store plaintext data keys. Only the encrypted data key should be stored alongside our encrypted data.
• Key Management: Regularly monitor and rotate our KMS Keys to enhance security.
• Compliance: Ensure our encryption practices comply with our organization's policies and regulatory requirements.

Conclusion

Envelope encryption provides a robust and scalable method for securing data in AWS, leveraging the managed services of AWS KMS for key management while allowing for efficient encryption of large data volumes. By following the steps outlined in this guide, we can implement envelope encryption in our applications, ensuring our data is protected with industry-standard security practices.