docs: @Override
    public void addEncryptionMetadata(StorageObjectMetadata meta,
                                      MatDesc matDesc,
                                      byte[] ivData,
                                      byte[] encKeK,
                                      long contentLength)
    {
      meta.addUserMetadata(getMatdescKey(),
                           matDesc.toString());
      meta.addUserMetadata(AMZ_KEY,
                           Base64.encodeAsString(encKeK));
      meta.addUserMetadata(AMZ_IV,
                           Base64.encodeAsString(ivData));
      meta.setContentLength(contentLength);
    }