AWS Key Management Service Construct Library
AWS CDK v1 has reached End-of-Support on 2023-06-01.
This package is no longer being updated, and users should migrate to AWS CDK v2.
For more information on how to migrate, see the Migrating to AWS CDK v2 guide.
Define a KMS key:
new kms.Key(this, 'MyKey', {
enableKeyRotation: true,
});
Define a KMS key with waiting period:
Specifies the number of days in the waiting period before AWS KMS deletes a CMK that has been removed from a CloudFormation stack.
const key = new kms.Key(this, 'MyKey', {
pendingWindow: Duration.days(10),
});
Add a couple of aliases:
const key = new kms.Key(this, 'MyKey');
key.addAlias('alias/foo');
key.addAlias('alias/bar');
Define a key with specific key spec and key usage:
Valid keySpec
values depends on keyUsage
value.
const key = new kms.Key(this, 'MyKey', {
keySpec: kms.KeySpec.ECC_SECG_P256K1,
keyUsage: kms.KeyUsage.SIGN_VERIFY,
});
Sharing keys between stacks
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
Import key by ARN
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:...');
myKeyImported.addAlias('alias/foo');
Note that a call to .addToResourcePolicy(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.
Import key by alias
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.
import * as cloudtrail from '@aws-cdk/aws-cloudtrail';
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.
Lookup key by alias
If you can't use a KMS key imported by alias (e.g. because you need access to the key id), you can lookup the key with Key.fromLookup()
.
In general, the preferred method would be to use Alias.fromAliasName()
which returns an IAlias
object which extends IKey
. However, some services need to have access to the underlying key id. In this case, Key.fromLookup()
allows to lookup the key id.
The result of the Key.fromLookup()
operation will be written to a file
called cdk.context.json
. You must commit this file to source control so
that the lookup values are available in non-privileged environments such
as CI build steps, and to ensure your template builds are repeatable.
Here's how Key.fromLookup()
can be used:
const myKeyLookup = kms.Key.fromLookup(this, 'MyKeyLookup', {
aliasName: 'alias/KeyAlias',
});
const role = new iam.Role(this, 'MyRole', {
assumedBy: new iam.ServicePrincipal('lambda.amazonaws.com'),
});
myKeyLookup.grantEncryptDecrypt(role);
Note that a call to .addToResourcePolicy(statement)
on myKeyLookup
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.
Key Policies
Controlling access and usage of KMS Keys requires the use of key policies (resource-based policies attached to the key);
this is in contrast to most other AWS resources where access can be entirely controlled with IAM policies,
and optionally complemented with resource policies. For more in-depth understanding of KMS key access and policies, see
KMS keys can be created to trust IAM policies. This is the default behavior for both the KMS APIs and in
the console. This behavior is enabled by the '@aws-cdk/aws-kms:defaultKeyPolicies' feature flag,
which is set for all new projects; for existing projects, this same behavior can be enabled by
passing the trustAccountIdentities
property as true
when creating the key:
new kms.Key(this, 'MyKey', { trustAccountIdentities: true });
With either the @aws-cdk/aws-kms:defaultKeyPolicies
feature flag set,
or the trustAccountIdentities
prop set, the Key will be given the following default key policy:
{
"Effect": "Allow",
"Principal": {"AWS": "arn:aws:iam::111122223333:root"},
"Action": "kms:*",
"Resource": "*"
}
This policy grants full access to the key to the root account user.
This enables the root account user -- via IAM policies -- to grant access to other IAM principals.
With the above default policy, future permissions can be added to either the key policy or IAM principal policy.
const key = new kms.Key(this, 'MyKey');
const user = new iam.User(this, 'MyUser');
key.grantEncrypt(user);
Adopting the default KMS key policy (and so trusting account identities)
solves many issues around cyclic dependencies between stacks.
Without this default key policy, future permissions must be added to both the key policy and IAM principal policy,
which can cause cyclic dependencies if the permissions cross stack boundaries.
(For example, an encrypted bucket in one stack, and Lambda function that accesses it in another.)
Appending to or replacing the default key policy
The default key policy can be amended or replaced entirely, depending on your use case and requirements.
A common addition to the key policy would be to add other key admins that are allowed to administer the key
(e.g., change permissions, revoke, delete). Additional key admins can be specified at key creation or after
via the grantAdmin
method.
const myTrustedAdminRole = iam.Role.fromRoleArn(this, 'TrustedRole', 'arn:aws:iam:....');
const key = new kms.Key(this, 'MyKey', {
admins: [myTrustedAdminRole],
});
const secondKey = new kms.Key(this, 'MyKey2');
secondKey.grantAdmin(myTrustedAdminRole);
Alternatively, a custom key policy can be specified, which will replace the default key policy.
Note: In applications without the '@aws-cdk/aws-kms:defaultKeyPolicies' feature flag set
and with trustedAccountIdentities
set to false (the default), specifying a policy at key creation appends the
provided policy to the default key policy, rather than replacing the default policy.
const myTrustedAdminRole = iam.Role.fromRoleArn(this, 'TrustedRole', 'arn:aws:iam:....');
const myCustomPolicy = new iam.PolicyDocument({
statements: [new iam.PolicyStatement({
actions: [
'kms:Create*',
'kms:Describe*',
'kms:Enable*',
'kms:List*',
'kms:Put*',
],
principals: [new iam.AccountRootPrincipal()],
resources: ['*'],
})],
});
const key = new kms.Key(this, 'MyKey', {
policy: myCustomPolicy,
});
Warning: Replacing the default key policy with one that only grants access to a specific user or role
runs the risk of the key becoming unmanageable if that user or role is deleted.
It is highly recommended that the key policy grants access to the account root, rather than specific principals.
See https://docs.aws.amazon.com/kms/latest/developerguide/key-policies.html for more information.