AWS KMS key management

Amazon RDS automatically integrates with AWS Key Management Service (AWS KMS) for key management. Amazon RDS uses envelope encryption. For more information about envelope encryption, see Envelope encryption in the AWS Key Management Service Developer Guide.

You can use two types of AWS KMS keys to encrypt your DB instances .

• If you want full control over a KMS key, you must create a customer managed key. For more information about customer managed keys, see Customer managed keys in the AWS Key Management Service Developer Guide.

• AWS managed keys are KMS keys in your account that are created, managed, and used on your behalf by an AWS service that is integrated with AWS KMS. By default, the RDS AWS managed key ( aws/rds) is used for encryption. You can't manage, rotate, or delete the RDS AWS managed key. For more information about AWS managed keys, see AWS managed keys in the AWS Key Management Service Developer Guide.

To manage KMS keys used for Amazon RDS encrypted DB instances , use the AWS Key Management Service (AWS KMS) in the AWS KMS console, the AWS CLI, or the AWS KMS API. To view audit logs of every action taken with an AWS managed or customer managed key, use AWS CloudTrail. For more information about key rotation, see Rotating AWS KMS keys.

Authorizing use of a customer managed key

When RDS uses a customer managed key in cryptographic operations, it acts on behalf of the user who is creating or changing the RDS resource.

To create an RDS resource using a customer managed key, a user must have permissions to call the following operations on the customer managed key:

• kms:CreateGrant

• kms:DescribeKey

You can specify these required permissions in a key policy, or in an IAM policy if the key policy allows it.

Tip

To follow the principle of least privilege, do not allow full access to kms:CreateGrant. Instead, use the kms:ViaService condition key to allow the user to create grants on the KMS key only when the grant is created on the user's behalf by an AWS service.

You can make the IAM policy stricter in various ways. For example, if you want to allow the customer managed key to be used only for requests that originate in RDS , use the kms:ViaService condition key with the rds.<region>.amazonaws.com value. Also, you can use the keys or values in the Amazon RDS encryption context as a condition for using the customer managed key for encryption.

For more information, see Allowing users in other accounts to use a KMS key in the AWS Key Management Service Developer Guide and Key policies in AWS KMS.

Amazon RDS encryption context

When RDS uses your KMS key, or when Amazon EBS uses the KMS key on behalf of RDS , the service specifies an encryption context. The encryption context is additional authenticated data (AAD) that AWS KMS uses to ensure data integrity. When an encryption context is specified for an encryption operation, the service must specify the same encryption context for the decryption operation. Otherwise, decryption fails. The encryption context is also written to your AWS CloudTrail logs to help you understand why a given KMS key was used. Your CloudTrail logs might contain many entries describing the use of a KMS key, but the encryption context in each log entry can help you determine the reason for that particular use.

At minimum, Amazon RDS always uses the DB instance ID for the encryption context, as in the following JSON-formatted example:

{ "aws:rds:db-id": "db-CQYSMDPBRZ7BPMH7Y3RTDG5QY" }

This encryption context can help you identify the DB instance for which your KMS key was used.

When your KMS key is used for a specific DB instance and a specific Amazon EBS volume, both the DB instance ID and the Amazon EBS volume ID are used for the encryption context, as in the following JSON-formatted example:

{
  "aws:rds:db-id": "db-BRG7VYS3SVIFQW7234EJQOM5RQ",
  "aws:ebs:id": "vol-ad8c6542"
}