Jun 17 2021
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Encrypt global data client-side with AWS KMS multi-Region keys

Today, AWS Key Management Service (AWS KMS) is introducing multi-Region keys, a new capability that lets you replicate keys from one Amazon Web Services (AWS) Region into another. Multi-Region keys are designed to simplify management of client-side encryption when your encrypted data has to be copied into other Regions for disaster recovery or is replicated in Amazon DynamoDB global tables.

In this blog post, we give an overview of how we got here and how to get started using multi-Region keys. We include a code example for multi-Region encryption of data in DynamoDB global tables.

How we got here

From its inception, AWS KMS has been strictly isolated to a single AWS Region for each implementation, with no sharing of keys, policies, or audit information across Regions. Region isolation can help you comply with security standards and data residency requirements. However, not sharing keys across Regions creates challenges when you need to move data that depends on those keys across Regions. AWS services that use your KMS keys for server-side encryption address this challenge by transparently re-encrypting data on your behalf using the KMS keys you designate in the destination Region. If you use client-side encryption, this work adds extra complexity and latency of re-encrypting between regionally isolated KMS keys.

Multi-Region keys are a new feature from AWS KMS for client-side applications that makes KMS-encrypted ciphertext portable across Regions. Multi-Region keys are a set of interoperable KMS keys that have the same key ID and key material, and that you can replicate to different Regions within the same partition. With symmetric multi-Region keys, you can encrypt data in one Region and decrypt it in a different Region. With asymmetric multi-Region keys, you encrypt, decrypt, sign, and verify messages in multiple Regions.

Multi-Region keys are supported in the AWS KMS console, the AWS KMS API, the AWS Encryption SDK, Amazon DynamoDB Encryption Client, and Amazon S3 Encryption Client. AWS services also let you configure multi-Region keys for server-side encryption in case you want the same key to protect data that needs both server-side and client-side encryption.

Getting started with multi-Region keys

To use multi-Region keys, you create a primary multi-Region key with a new key ID and key material. Then, you use the primary key to create a related multi-Region replica key in a different Region of the same AWS partition. Replica keys are KMS keys that can be used independently; they aren’t a pointer to the primary key. The primary and replica keys share only certain properties, including their key ID, key rotation, and key origin. In all other aspects, every multi-Region key, whether primary or replica, is a fully functional, independent KMS key resource with its own key policy, aliases, grants, key description, lifecycle, and other attributes. The key Amazon Resource Names (ARN) of related multi-Region keys differ only in the Region portion, as shown in the following figure (Figure 1).

Figure 1: Multi-Region keys have unique ARNs but identical key IDs

Figure 1: Multi-Region keys have unique ARNs but identical key IDs

You cannot convert an existing single-Region key to a multi-Region key. This design ensures that all data protected with existing single-Region keys maintain the same data residency and data sovereignty properties.

When to use multi-Region keys

You can use multi-Region keys in any client-side application. Since multi-Region keys avoid cross-Region calls, they’re especially useful for scenarios where you don’t want to depend on another Region or incur the latency of a cross-Region call. For example, disaster recovery, global data management, distributed signing applications, and active-active applications that span multiple Regions can all benefit from using multi-Region keys. You can also create and use multi-Region keys in a single Region and choose to replicate those keys at some later date when you need to move protected data to additional Regions.

Note: If your application will run in only one Region, you should continue to use single-Region keys to benefit from their data isolation properties.

One significant benefit of multi-Region keys is using them with DynamoDB global tables. Let’s explore that interaction in detail.

Using multi-Region keys with DynamoDB global tables

AWS KMS multi-Region keys (MRKs) can be used with the DynamoDB Encryption Client to protect data in DynamoDB global tables. You can configure the DynamoDB Encryption Client to call AWS KMS for decryption in a different Region than the one in which the data was encrypted, as shown in the following figure (Figure 2). This is useful for disaster recovery, or simply to improve performance when using DynamoDB in a globally distributed application.

Figure 2: Using multi-Region keys with DynamoDB global tables

Figure 2: Using multi-Region keys with DynamoDB global tables

The steps described in Figure 2 are:

  1. Encrypt record with primary MRK
  2. Put encrypted record
  3. Global table replication
  4. Get encrypted record
  5. Decrypt record with replica MRK

Create a multi-Region primary key

Begin by creating a multi-Region primary key and replicating it into your backup Regions. We’ll assume that you’ve created a DynamoDB global table that’s replicated to the same Regions.

Configure the DynamoDB Encryption Client to encrypt records

To use AWS KMS multi-Region keys, you need to configure the DynamoDB Encryption Client with the Region you want to call, which is typically the Region where the application is running. Then, you need to configure the ARN of the KMS key you want to use in that Region.

This example encrypts records in us-east-1 (US East (N. Virginia)) and decrypts records in us-west-2 (US West (Oregon)). If you use the following example configuration code, be sure to replace the example key ARNs with valid key ARNs for your multi-Region keys.

// Specify the multi-Region key in the us-east-1 Region
String encryptRegion = "us-east-1";
String cmkArnEncrypt = "arn:aws:kms:us-east-1:<111122223333>:key/<mrk-1234abcd12ab34cd56ef12345678990ab>"; // Set up SDK clients for KMS and DDB in us-east-1
AWSKMS kmsEncrypt = AWSKMSClientBuilder.standard().withRegion(encryptRegion).build();
AmazonDynamoDB ddbEncrypt = AmazonDynamoDBClientBuilder.standard().withRegion(encryptRegion).build(); // Configure the example global table
String tableName = "global-table-example";
String employeeIdAttribute = "employeeId";
String nameAttribute = "name"; // Configure attribute actions for the Dynamo DB Encryption Client
// Sign the employee ID field
// Encrypt and sign the name field
Map<String, Set<EncryptionFlags>> actions = new HashMap<>();
actions.put(employeeIdAttribute, EnumSet.of(EncryptionFlags.SIGN));
actions.put(nameAttribute, EnumSet.of(EncryptionFlags.ENCRYPT, EncryptionFlags.SIGN)); // Set an encryption context. This is an optional best practice.
final EncryptionContext encryptionContext = new EncryptionContext.Builder() .withTableName(tableName) .withHashKeyName(employeeIdAttribute) .build(); // Use the Direct KMS materials provider and the DynamoDB encryptor
// Specify the key ARN of the multi-Region key in us-east-1
DirectKmsMaterialProvider cmpEncrypt = new DirectKmsMaterialProvider(kmsEncrypt, cmkArnEncrypt);
DynamoDBEncryptor encryptor = DynamoDBEncryptor.getInstance(cmpEncrypt); // Create a record, encrypt it, // and put it in the DynamoDB global table
Map<String, AttributeValue> rec = new HashMap<>();
rec.put(nameAttribute, new AttributeValue().withS("Andy"));
rec.put(employeeIdAttribute, new AttributeValue().withS("1234")); final Map<String, AttributeValue> encryptedRecord = encryptor.encryptRecord(rec, actions, encryptionContext);
ddbEncrypt.putItem(tableName, encryptedRecord);

When you save the newly encrypted record, DynamoDB global tables automatically replicates this encrypted record to the replica tables in the us-west-2 Region.

Configure the DynamoDB Encryption Client to decrypt data

Now you’re ready to configure a DynamoDB client to decrypt the record in us-west-2 where both the replica table and the replica multi-Region key exist.

// Specify the Region and key ARN to use when decrypting String decryptRegion = "us-west-2";
String cmkArnDecrypt = "arn:aws:kms:us-west-2:<111122223333>:key/<mrk-1234abcd12ab34cd56ef12345678990ab>"; // Set up SDK clients for KMS and DDB in us-west-2
AWSKMS kmsDecrypt = AWSKMSClientBuilder.standard() .withRegion(decryptRegion) .build(); AmazonDynamoDB ddbDecrypt = AmazonDynamoDBClientBuilder.standard() .withRegion(decryptRegion) .build(); // Configure the DynamoDB Encryption Client
// Use the Direct KMS materials provider and the DynamoDB encryptor
// Specify the key ARN of the multi-Region key in us-west-2
final DirectKmsMaterialProvider cmpDecrypt = new DirectKmsMaterialProvider(kmsDecrypt, cmkArnDecrypt);
final DynamoDBEncryptor decryptor = DynamoDBEncryptor.getInstance(cmpDecrypt); // Set up your query
Map<String, AttributeValue> query = new HashMap<>();
query.put(employeeIdAttribute, new AttributeValue().withS("1234")); // Get a record from DDB and decrypt it
final Map<String, AttributeValue> retrievedRecord = ddbDecrypt.getItem(tableName, query).getItem();
final Map<String, AttributeValue> decryptedRecord = decryptor.decryptRecord(retrievedRecord, actions, encryptionContext);

Note: This example encrypts with the primary multi-Region key and then decrypts with a replica multi-Region key. The process could also be reversed—every multi-Region key can be used in the encryption or decryption of data.

Summary

In this blog post, we showed you how to use AWS KMS multi-Region keys with client-side encryption to help secure data in global applications without sacrificing high availability or low latency. We also showed you how you can start working with a global application with a brief example of using multi-Region keys with the DynamoDB Encryption Client and DynamoDB global tables.

This blog post is a brief introduction to the ways you can use multi-Region keys. We encourage you to read through the Using multi-Region keys topic to learn more about their functionality and design. You’ll learn about:

If you have feedback about this post, submit comments in the Comments section below. If you have questions about this post, start a new thread on the AWS KMS forum.

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Author

Jeremy Stieglitz

Jeremy is the Principal Product Manager for AWS Key Management Service (KMS) where he drives global product strategy and roadmap for AWS KMS. Jeremy has more than 20 years of experience defining new products and platforms, launching and scaling cryptography solutions, and driving end-to-end product strategies. Jeremy is the author or co-author of 23 patents in network security, user authentication and network automation and control.

Author

Peter Zieske

Peter is a Senior Software Developer on the AWS Key Management Service team, where he works on developing features on the service-side front-end. Outside of work, he enjoys building with LEGO, gaming, and spending time with family.

Author

Ben Farley

Ben is a Senior Software Developer on the AWS Crypto Tools team, where he works on client-side encryption libraries that help customers protect their data. Before that, he spent time focusing on the scalability and availability of services like AWS Identity and Access Management and AWS Key Management Service. Outside of work, he likes to explore the mountains with his fiancée and dog.

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