copySource:        copySource,
		metadata:          cloneMSS(oi.UserDefined),
	}

	if w.copySource {
		w.customerKeyHeader = h.Get(xhttp.AmzServerSideEncryptionCopyCustomerKey)
	}

	if err := w.buildDecrypter(w.parts[w.partIndex].Number); err != nil {
		return nil, err
	}

	return w, nil
}

// DecryptBlocksReader - decrypts multipart parts, while implementing
// a io.Reader compatible interface.