summaryrefslogtreecommitdiff
path: root/src/leap/bitmask/bonafide/_srp.py
blob: b0dd83fff323c7a026cd507d581d200750bc0648 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
# -*- coding: utf-8 -*-
# _srp.py
# Copyright (C) 2015 LEAP
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

"""
SRP Authentication.
"""

import binascii
import json

import srp


class SRPAuthMechanism(object):

    """
    Implement a protocol-agnostic SRP Authentication mechanism.
    """

    def __init__(self, username, password):
        self.username = username
        self.srp_user = srp.User(username, password,
                                 srp.SHA256, srp.NG_1024)
        _, A = self.srp_user.start_authentication()
        self.A = A
        self.M = None
        self.M2 = None

    def get_handshake_params(self):
        return {'login': bytes(self.username),
                'A': binascii.hexlify(self.A)}

    def process_handshake(self, handshake_response):
        challenge = json.loads(handshake_response)
        self._check_for_errors(challenge)
        salt = challenge.get('salt', None)
        B = challenge.get('B', None)
        unhex_salt, unhex_B = self._unhex_salt_B(salt, B)
        self.M = self.srp_user.process_challenge(unhex_salt, unhex_B)

    def get_authentication_params(self):
        # It looks A is not used server side
        return {'client_auth': binascii.hexlify(self.M),
                'A': binascii.hexlify(self.A)}

    def process_authentication(self, authentication_response):
        auth = json.loads(authentication_response)
        self._check_for_errors(auth)
        uuid = auth.get('id', None)
        token = auth.get('token', None)
        self.M2 = auth.get('M2', None)
        self._check_auth_params(uuid, token, self.M2)
        return uuid, token

    def verify_authentication(self):
        unhex_M2 = _safe_unhexlify(self.M2)
        self.srp_user.verify_session(unhex_M2)
        assert self.srp_user.authenticated()

    def _check_for_errors(self, response):
        if 'errors' in response:
            msg = response['errors']['base']
            raise SRPAuthError(unicode(msg).encode('utf-8'))

    def _unhex_salt_B(self, salt, B):
        if salt is None:
            raise SRPAuthNoSalt()
        if B is None:
            raise SRPAuthNoB()
        try:
            unhex_salt = _safe_unhexlify(salt)
            unhex_B = _safe_unhexlify(B)
        except (TypeError, ValueError) as e:
            raise SRPAuthBadDataFromServer(str(e))
        return unhex_salt, unhex_B

    def _check_auth_params(self, uuid, token, M2):
        if not all((uuid, token, M2)):
            msg = '%s' % str((M2, uuid, token))
            raise SRPAuthBadDataFromServer(msg)


class SRPSignupMechanism(object):

    """
    Implement a protocol-agnostic SRP Registration mechanism.
    """

    def get_signup_params(self, username, password):
        salt, verifier = srp.create_salted_verification_key(
            bytes(username), bytes(password),
            srp.SHA256, srp.NG_1024)
        user_data = {
            'user[login]': username,
            'user[password_salt]': binascii.hexlify(salt),
            'user[password_verifier]': binascii.hexlify(verifier)}
        return user_data

    def process_signup(self, signup_response):
        signup = json.loads(signup_response)
        errors = signup.get('errors')
        if errors:
            msg = 'username ' + errors.get('login')[0]
            raise SRPRegistrationError(msg)
        else:
            username = signup.get('login')
            return username


def _safe_unhexlify(val):
    return binascii.unhexlify(val) \
        if (len(val) % 2 == 0) else binascii.unhexlify('0' + val)


class SRPAuthError(Exception):
    """
    Base exception for srp authentication errors
    """


class SRPAuthNoSalt(SRPAuthError):
    message = 'The server didn\'t send the salt parameter'


class SRPAuthNoB(SRPAuthError):
    message = 'The server didn\'t send the B parameter'


class SRPAuthBadDataFromServer(SRPAuthError):
    pass


class SRPRegistrationError(Exception):
    pass