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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.
import base64
import struct
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
_ALLOWED_HASH_TYPES = typing.Union[SHA1, SHA256, SHA512]
def _generate_uri(
hotp: "HOTP",
type_name: str,
account_name: str,
issuer: typing.Optional[str],
extra_parameters: typing.List[typing.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)
uriparts = {
"type": type_name,
"label": (
"%s:%s" % (quote(issuer), quote(account_name))
if issuer
else quote(account_name)
),
"parameters": urlencode(parameters),
}
return "otpauth://{type}/{label}?{parameters}".format(**uriparts)
class HOTP(object):
def __init__(
self,
key: bytes,
length: int,
algorithm: _ALLOWED_HASH_TYPES,
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 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
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(struct.pack(">Q", counter))
hmac_value = ctx.finalize()
offset = hmac_value[len(hmac_value) - 1] & 0b1111
p = hmac_value[offset : offset + 4]
return struct.unpack(">I", p)[0] & 0x7FFFFFFF
def get_provisioning_uri(
self, account_name: str, counter: int, issuer: typing.Optional[str]
) -> str:
return _generate_uri(
self, "hotp", account_name, issuer, [("counter", int(counter))]
)