Should I use an AWS KMS-managed key or a custom AWS KMS key to encrypt my objects on Amazon S3?

Last updated: 2020-10-21

AWS KMS manages the default aws/s3 CMK, but you have full control over a custom CMK.

Note: The name of the CMK is aws/s3 in the Amazon S3 console, but you don't specify that name or ID if you use the AWS Command Line Interface (AWS CLI).

Consider using the default aws/s3 CMK if:

• You're uploading or accessing S3 objects using AWS Identity and Access Management (IAM) principals that are in the same AWS account as the CMK.
• You don't want to manage policies for the CMK.
• You don't want to rotate the CMK.

To encrypt an object using the default aws/s3 CMK, define the encryption method as SSE-KMS during the upload, but don't specify a key:

Note: If you receive errors when running AWS CLI commands, make sure that you’re using the most recent version of the AWS CLI.

Consider using a custom CMK if:

• You want to create, rotate, disable, or define access controls for the CMK.
• You want to grant cross-account access to your S3 objects. You can configure the policy of a custom CMK to allow access from another account.

To encrypt an object using a custom CMK that you created, define the encryption method as SSE-KMS during the upload. Then, specify your custom CMK as the key (--sse-kms-key-id):

To control access to your custom CMK, modify the key policy. For more information on how to create an AWS KMS key policy, see Example key policy.