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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 annotations
import base64
import typing
from urllib.parse import quote, urlencode
from cryptography.hazmat.primitives import constant_time, hmac
from cryptography.hazmat.primitives.hashes import SHA1, SHA256, SHA512
from cryptography.hazmat.primitives.twofactor import InvalidToken
HOTPHashTypes = typing.Union[SHA1, SHA256, SHA512]
def _generate_uri(
hotp: HOTP,
type_name: str,
account_name: str,
issuer: str | None,
extra_parameters: list[tuple[str, int]],
) -> str:
parameters = [
("digits", hotp._length),
("secret", base64.b32encode(hotp._key)),
("algorithm", hotp._algorithm.name.upper()),
]
if issuer is not None:
parameters.append(("issuer", issuer))
parameters.extend(extra_parameters)
label = (
f"{quote(issuer)}:{quote(account_name)}"
if issuer
else quote(account_name)
)
return f"otpauth://{type_name}/{label}?{urlencode(parameters)}"
class HOTP:
def __init__(
self,
key: bytes,
length: int,
algorithm: HOTPHashTypes,
backend: typing.Any = None,
enforce_key_length: bool = True,
) -> None:
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, int):
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 and 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
def generate(self, counter: int) -> bytes:
truncated_value = self._dynamic_truncate(counter)
hotp = truncated_value % (10**self._length)
return "{0:0{1}}".format(hotp, self._length).encode()
def verify(self, hotp: bytes, counter: int) -> None:
if not constant_time.bytes_eq(self.generate(counter), hotp):
raise InvalidToken("Supplied HOTP value does not match.")
def _dynamic_truncate(self, counter: int) -> int:
ctx = hmac.HMAC(self._key, self._algorithm)
ctx.update(counter.to_bytes(length=8, byteorder="big"))
hmac_value = ctx.finalize()
offset = hmac_value[len(hmac_value) - 1] & 0b1111
p = hmac_value[offset : offset + 4]
return int.from_bytes(p, byteorder="big") & 0x7FFFFFFF
def get_provisioning_uri(
self, account_name: str, counter: int, issuer: str | None
) -> str:
return _generate_uri(
self, "hotp", account_name, issuer, [("counter", int(counter))]
)
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