packer-cn/website/source/partials/builders/_aws-common-opional-fields.html.md

• kms_key_id (string) - ID, alias or ARN of the KMS key to use for boot volume encryption. This only applies to the main region, other regions where the AMI will be copied will be encrypted by the default EBS KMS key. For valid formats see KmsKeyId in the AWS API docs - CopyImage. This field is validated by Packer, when using an alias, you will have to prefix kms_key_id with alias/.