Source code for cryptography.hazmat.primitives.twofactor.hotp

# 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

import struct

import six

from cryptography.exceptions import (
    UnsupportedAlgorithm, _Reasons
from cryptography.hazmat.backends.interfaces import HMACBackend
from cryptography.hazmat.primitives import constant_time, hmac
from cryptography.hazmat.primitives.hashes import SHA1, SHA256, SHA512
from cryptography.hazmat.primitives.twofactor import InvalidToken
from cryptography.hazmat.primitives.twofactor.utils import _generate_uri

[docs]class HOTP(object): def __init__(self, key, length, algorithm, backend, enforce_key_length=True): if not isinstance(backend, HMACBackend): raise UnsupportedAlgorithm( "Backend object does not implement HMACBackend.", _Reasons.BACKEND_MISSING_INTERFACE ) if len(key) < 16 and enforce_key_length is True: raise ValueError("Key length has to be at least 128 bits.") if not isinstance(length, six.integer_types): raise TypeError("Length parameter must be an integer type.") if length < 6 or length > 8: raise ValueError("Length of HOTP has to be between 6 to 8.") if not isinstance(algorithm, (SHA1, SHA256, SHA512)): raise TypeError("Algorithm must be SHA1, SHA256 or SHA512.") self._key = key self._length = length self._algorithm = algorithm self._backend = backend
[docs] def generate(self, counter): truncated_value = self._dynamic_truncate(counter) hotp = truncated_value % (10 ** self._length) return "{0:0{1}}".format(hotp, self._length).encode()
[docs] def verify(self, hotp, counter): if not constant_time.bytes_eq(self.generate(counter), hotp): raise InvalidToken("Supplied HOTP value does not match.")
def _dynamic_truncate(self, counter): ctx = hmac.HMAC(self._key, self._algorithm, self._backend) ctx.update(struct.pack(">Q", counter)) hmac_value = ctx.finalize() offset = six.indexbytes(hmac_value, len(hmac_value) - 1) & 0b1111 p = hmac_value[offset:offset + 4] return struct.unpack(">I", p)[0] & 0x7fffffff
[docs] def get_provisioning_uri(self, account_name, counter, issuer): return _generate_uri(self, "hotp", account_name, issuer, [ ("counter", int(counter)), ])