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# -*- coding: utf-8 -*-
# SPDX-License-Identifier: BSD-2-Clause-FreeBSD
#
# Copyright (c) 2020, Simeon Simeonov
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright notice,
# this list of conditions and the following disclaimer in the documentation
# and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
"""A pure Python implementation of the RFC-2289 OTP server"""
import binascii
import hashlib
from .generator import (OTP_ALGO_MD5,
OTPGenerator,
OTPGeneratorException)
class OTPStateException(Exception):
"""OTPStateException class"""
class OTPInvalidResponse(Exception):
"""OTPInvalidResponse class"""
class OTPState:
"""
OTPState class
The OTPState class represents a single state on the server side that can:
- generate a challenge
- validate the corresponding generated response from the generator
"""
def __init__(self, ot_hex, current_step, seed, hash_algo=OTP_ALGO_MD5):
"""
Constructs an OTPState object with the given arguments.
Keyword Arguments:
:param ot_hex: The one-time hex from the last successful
authentication or the first OTP of a newly
initialized sequence
:type ot_hex: str
:param current_step: The current step that is sent with the challenge
:type current_step: int
:param seed: The seed that is sent with the challenge
:type seed: str
:param hash_algo: The hash algo, defaults to OTP_ALGO_MD5
:type hash_algo: int or str
:raises OTPStateException: In case the input does not validate
"""
# enforce the rfc2289 constraints
try:
self._seed = OTPGenerator.validate_seed(seed)
self._hash_algo = OTPGenerator.validate_hash_algo(hash_algo)
self._step = OTPGenerator.validate_step(current_step)
except OTPGeneratorException as exp:
raise OTPStateException(exp.args[0])
self._current_digest = self.validate_hex(ot_hex)
self._new_digest_hex = None # set upon a successful validation
def __str__(self):
"""Duplicate the challenge string"""
return f'otp-{self._hash_algo} {self._step} {self._seed} '
@property
def challenge_string(self):
"""challenge_string-property"""
# RFC-2289: "...the entire challenge string MUST be
# terminated with either a space or a new line."
return f'otp-{self._hash_algo} {self._step} {self._seed} '
@property
def validated(self):
"""validated-property"""
return bool(self._new_digest_hex)
@staticmethod
def response_to_bytes(response):
"""
A wrapper that handles/validates the response as specified by RFC-2289.
The method first checks if response is a token and tries to convert
it to bytes. If that fails, the method assumes that response is a hex.
If neither of those attempts succeeds OTPInvalidResponse is raised.
It is up to the caller to run another iteration and compare the result
to an existing digest in this state.
:param response: The response to this state (its challenge)
:type response: str
:raises OTPInvalidResponse: If the response is corrupt / illegal,
but not if it simply does not validate
:return: The bytes representation of response (if any)
:rtype: bytes
"""
try:
return OTPGenerator.tokens_to_bytes(response)
except OTPGeneratorException:
# now assume hex...
try:
return OTPState.validate_hex(response)
except OTPStateException:
raise OTPInvalidResponse(
'The response is neither a valid token or hex')
@staticmethod
def validate_hex(ot_hex):
"""
Validates the provided hexidigest.
:param ot_hex: The one-time hex to validate
:type ot_hex: str
:raises OTPStateException: In case hex does not validate
:return: The validated hex (without leading 0x) converted to bytes
:rtype: bytes
"""
if not isinstance(ot_hex, str):
raise OTPStateException('OT-hex must be a str')
if ot_hex.startswith('0x'):
ot_hex = ot_hex[2:]
ot_hex = ot_hex.strip().lower()
if len(ot_hex) != 16:
raise OTPStateException('The length of the hex should be 16 '
'(representing 64 bits digest)')
try:
return binascii.unhexlify(ot_hex)
except binascii.Error:
raise OTPStateException('Invalid OT-hex')
def response_validates(self, response, store_valid_response=True):
"""
Validates the incoming response as specified by RFC-2289.
:param response: The response to this state (its challenge)
:type response: str
:param store_valid_response: Should a valid response be stored
:type store_valid_response: bool
:raises OTPInvalidResponse: If the response does not match this state
:return: Returns True if response validates, False otherwise
:rtype: bool
"""
# self.response_to_bytes raises OTPInvalidResponse in case response
# is corrupt or in a wrong format
response_bytes = self.response_to_bytes(response)
if self._hash_algo == 'md5':
digest = hashlib.md5(response_bytes).digest()
if (
OTPGenerator.strxor(digest[0:8], digest[8:]) ==
self._current_digest
):
if store_valid_response:
self._new_digest_hex = binascii.hexlify(
response_bytes).decode()
return True
return False
if self._hash_algo == 'sha1':
digest = hashlib.sha1(response_bytes).digest()
if (
OTPGenerator.sha1_digest_folding(
hashlib.sha1(
response_bytes).digest()) == self._current_digest
):
if store_valid_response:
self._new_digest_hex = binascii.hexlify(
response_bytes).decode()
return True
return False
# this should not happen since the hash_algo is validated by the caller
raise OTPInvalidResponse(f'Ivalid hash_algo: {self._hash_algo}')
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