// multi-part PUT request. It derives an unique encryption key from
// the partID and the object key.
func EncryptMultiPart(r io.Reader, partID int, key ObjectKey) io.Reader {
	partKey := key.DerivePartKey(uint32(partID))
	return EncryptSinglePart(r, ObjectKey(partKey))
}

// DecryptSinglePart decrypts an io.Writer which must an object
// uploaded with the single-part PUT API. The offset and length

			return
		}
		copy(objectEncryptionKey[:], key)

		var nonce [12]byte
		tmp := sha256.Sum256(fmt.Append(nil, uploadID, partID))
		copy(nonce[:], tmp[:12])

		partEncryptionKey := objectEncryptionKey.DerivePartKey(uint32(partID))
		encReader, err := sio.EncryptReader(reader, sio.Config{
			Key:   partEncryptionKey[:],
			Nonce: &nonce,
		})
		if err != nil {
			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)