// In case of SSE-S3, the ETag of an object is computed the same as
// for single resp. multipart plaintext objects. In particular,
// the ETag of a singlepart SSE-S3 object is its content MD5.
//
// In case of SSE-C and SSE-KMS, the ETag of an object is computed
// differently. For singlepart uploads the ETag is not the content
// MD5 of the object. For multipart uploads the ETag is also not