def parse_mode(cipher_nme):
    """
    Parse the cipher mode from cipher name
    e.g. aes-128-gcm, the mode is gcm
    :param cipher_nme: str cipher name, aes-128-cfb, aes-128-gcm ...
    :return: str/None The mode, cfb, gcm ...
    """
    hyphen = cipher_nme.rfind('-')
    if hyphen > 0:
        return cipher_nme[hyphen:]
    return None