contentMd5

The Base64 encoded 128-bit MD5 digest of the message (without the headers) according to RFC 1864. This header can be used as a message integrity check to verify that the data is the same data that was originally sent. Although it is optional, we recommend using the Content-MD5 mechanism as an end-to-end integrity check. For more information about REST request authentication, see REST Authentication.

The Content-MD5 or x-amz-sdk-checksum-algorithm header is required for any request to upload an object with a retention period configured using Amazon S3 Object Lock. For more information, see Uploading objects to an Object Lock enabled bucket in the Amazon S3 User Guide.

This functionality is not supported for directory buckets.