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# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.
from __future__ import absolute_import, division, print_function
from cryptography.exceptions import (
InvalidToken, UnsupportedAlgorithm, _Reasons
)
from cryptography.hazmat.backends.interfaces import HMACBackend
from cryptography.hazmat.primitives import constant_time
from cryptography.hazmat.primitives.twofactor.hotp import HOTP
class TOTP(object):
def __init__(self, key, length, algorithm, time_step, backend):
if not isinstance(backend, HMACBackend):
raise UnsupportedAlgorithm(
"Backend object does not implement HMACBackend.",
_Reasons.BACKEND_MISSING_INTERFACE
)
self._time_step = time_step
self._hotp = HOTP(key, length, algorithm, backend)
def generate(self, time):
counter = int(time / self._time_step)
return self._hotp.generate(counter)
def verify(self, totp, time):
if not constant_time.bytes_eq(self.generate(time), totp):
raise InvalidToken("Supplied TOTP value does not match.")
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