@aws-cdk/aws-kms

What is @aws-cdk/aws-kms?

@aws-cdk/aws-kms is an AWS CDK library that allows you to define and manage AWS Key Management Service (KMS) resources in your AWS infrastructure as code. It provides constructs for creating and managing KMS keys, aliases, and grants, enabling secure encryption and decryption of data.

What are @aws-cdk/aws-kms's main functionalities?

Create a KMS Key

This code sample demonstrates how to create a new KMS key with key rotation enabled and an alias using the AWS CDK.

const cdk = require('@aws-cdk/core');
const kms = require('@aws-cdk/aws-kms');

const app = new cdk.App();
const stack = new cdk.Stack(app, 'MyStack');

const key = new kms.Key(stack, 'MyKey', {
  enableKeyRotation: true,
  alias: 'alias/my-key'
});

app.synth();

Create a KMS Alias

This code sample demonstrates how to create a new KMS alias that points to an existing KMS key using the AWS CDK.

const cdk = require('@aws-cdk/core');
const kms = require('@aws-cdk/aws-kms');

const app = new cdk.App();
const stack = new cdk.Stack(app, 'MyStack');

const key = new kms.Key(stack, 'MyKey');

const alias = new kms.Alias(stack, 'MyAlias', {
  aliasName: 'alias/my-alias',
  targetKey: key
});

app.synth();

Grant Permissions to a KMS Key

This code sample demonstrates how to grant encrypt and decrypt permissions to an IAM user for a KMS key using the AWS CDK.

const cdk = require('@aws-cdk/core');
const kms = require('@aws-cdk/aws-kms');
const iam = require('@aws-cdk/aws-iam');

const app = new cdk.App();
const stack = new cdk.Stack(app, 'MyStack');

const key = new kms.Key(stack, 'MyKey');

const user = new iam.User(stack, 'MyUser');

key.grantEncryptDecrypt(user);

app.synth();

Other packages similar to @aws-cdk/aws-kms

aws-sdk

The aws-sdk package is the official AWS SDK for JavaScript, which provides a comprehensive set of tools for interacting with AWS services, including KMS. Unlike @aws-cdk/aws-kms, which is used for defining infrastructure as code, aws-sdk is used for making API calls to AWS services directly from your application code.

serverless

The serverless package is a framework for building and deploying serverless applications on AWS and other cloud providers. It includes support for managing AWS KMS keys as part of your serverless infrastructure. While it provides similar functionality for managing KMS keys, it is more focused on serverless architectures compared to the broader infrastructure management capabilities of @aws-cdk/aws-kms.

terraform

Terraform is an open-source infrastructure as code tool that allows you to define and manage cloud resources, including AWS KMS keys, using a declarative configuration language. It provides similar functionality to @aws-cdk/aws-kms but uses a different syntax and approach to infrastructure management.

README

AWS Key Management Service Construct Library

---

---

Define a KMS key:

import * as kms from '@aws-cdk/aws-kms';

new kms.Key(this, 'MyKey', {
    enableKeyRotation: true
});

Add a couple of aliases:

const key = new kms.Key(this, 'MyKey');
key.addAlias('alias/foo');
key.addAlias('alias/bar');

Sharing keys between stacks

see Trust Account Identities for additional details

To use a KMS key in a different stack in the same CDK application, pass the construct to the other stack:

sharing key between stacks

Importing existing keys

see Trust Account Identities for additional details

To use a KMS key that is not defined in this CDK app, but is created through other means, use Key.fromKeyArn(parent, name, ref):

const myKeyImported = kms.Key.fromKeyArn(this, 'MyImportedKey', 'arn:aws:...');

// you can do stuff with this imported key.
myKeyImported.addAlias('alias/foo');

Note that a call to .addToPolicy(statement) on myKeyImported will not have an affect on the key's policy because it is not owned by your stack. The call will be a no-op.

If a Key has an associated Alias, the Alias can be imported by name and used in place of the Key as a reference. A common scenario for this is in referencing AWS managed keys.

const myKeyAlias = kms.Alias.fromAliasName(this, 'myKey', 'alias/aws/s3');
const trail = new cloudtrail.Trail(this, 'myCloudTrail', {
    sendToCloudWatchLogs: true,
    kmsKey: myKeyAlias
});

Note that calls to addToResourcePolicy and grant* methods on myKeyAlias will be no-ops, and addAlias and aliasTargetKey will fail, as the imported alias does not have a reference to the underlying KMS Key.

Trust Account Identities

KMS keys can be created to trust IAM policies. This is the default behavior in the console and is described here. This same behavior can be enabled by:

new Key(stack, 'MyKey', { trustAccountIdentities: true });

Using trustAccountIdentities solves many issues around cyclic dependencies between stacks. The most common use case is creating an S3 Bucket with CMK default encryption which is later accessed by IAM roles in other stacks.

stack-1 (bucket and key created)

// ... snip
const myKmsKey = new kms.Key(this, 'MyKey', { trustAccountIdentities: true });

const bucket = new Bucket(this, 'MyEncryptedBucket', {
    bucketName: 'myEncryptedBucket',
    encryption: BucketEncryption.KMS,
    encryptionKey: myKmsKey
});

stack-2 (lambda that operates on bucket and key)

// ... snip

const fn = new lambda.Function(this, 'MyFunction', {
  runtime: lambda.Runtime.NODEJS_10_X,
  handler: 'index.handler',
  code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')),
});

const bucket = s3.Bucket.fromBucketName(this, 'BucketId', 'myEncryptedBucket');

const key = kms.Key.fromKeyArn(this, 'KeyId', 'arn:aws:...'); // key ARN passed via stack props

bucket.grantReadWrite(fn);
key.grantEncryptDecrypt(fn);

The challenge in this scenario is the KMS key policy behavior. The simple way to understand this, is IAM policies for account entities can only grant the permissions granted to the account root principle in the key policy. When trustAccountIdentities is true, the following policy statement is added:

{
  "Sid": "Enable IAM User Permissions",
  "Effect": "Allow",
  "Principal": {"AWS": "arn:aws:iam::111122223333:root"},
  "Action": "kms:*",
  "Resource": "*"
}

As the name suggests this trusts IAM policies to control access to the key. If account root does not have permissions to the specific actions, then the key policy and the IAM policy for the entity (e.g. Lambda) both need to grant permission.

Changelog

1.61.1 (2020-08-28)

Bug Fixes

• cli: unable to upgrade new style bootstrap to version (#10030) (8d3e422), closes #10016