def _pad_bytes(request_bytes):
    """
    :type request_bytes: bytes

    :rtype: bytes
    """

    padding_length = (_BLOCK_SIZE - len(request_bytes) % _BLOCK_SIZE)
    padding_character = bytes(bytearray([padding_length]))

    return request_bytes + padding_character * padding_length
:type request_bytes: bytes

    :rtype: bytes