JezK
Edit File: hotp.py
# 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 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) 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: _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(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: typing.Optional[str] ) -> str: return _generate_uri( self, "hotp", account_name, issuer, [("counter", int(counter))] )