class Security:     def __init__(self):        import os        env = os.environ        if env.has_key('PYTHON_KEYFILE'):            keyfile = env['PYTHON_KEYFILE']        else:            keyfile = '.python_keyfile'            if env.has_key('HOME'):                keyfile = os.path.join(env['HOME'], keyfile)            if not os.path.exists(keyfile):                import sys                for dir in sys.path:                    kf = os.path.join(dir, keyfile)                    if os.path.exists(kf):                        keyfile = kf                        break        try:            self._key = eval(open(keyfile).readline())        except IOError:            raise IOError, "python keyfile %s: cannot open" % keyfile     def _generate_challenge(self):        import random        return random.randint(100, 100000)     def _compare_challenge_response(self, challenge, response):        return self._encode_challenge(challenge) == response     def _encode_challenge(self, challenge):        p, m = self._key        return pow(long(challenge), p, m)