// An S3 implementation has to remember the content MD5 of objects
// in case of SSE-S3. However, storing the ETag of an encrypted
// object in plaintext may reveal some information about the object.
// For example, two objects with the same ETag are identical with
// a very high probability.
//
// Therefore, an S3 implementation may encrypt an ETag before storing
// it. In this case, the stored ETag may not be a well-formed S3 ETag.