Indicates whether Amazon S3 server-side encryption with Amazon S3-managed keys (SSE_S3), server-side encryption with KMS-managed keys (SSE_KMS), or client-side encryption with KMS-managed keys (CSE_KMS) is used.
SSE_S3
SSE_KMS
CSE_KMS
For SSE_KMS and CSE_KMS, this is the KMS key ARN or ID.