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
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
|
# Copyright (C) 2003-2007 Robey Pointer <robeypointer@gmail.com>
#
# This file is part of paramiko.
#
# Paramiko is free software; you can redistribute it and/or modify it under the
# terms of the GNU Lesser General Public License as published by the Free
# Software Foundation; either version 2.1 of the License, or (at your option)
# any later version.
#
# Paramiko is distrubuted 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 Lesser General Public License for more
# details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with Paramiko; if not, write to the Free Software Foundation, Inc.,
# 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
"""
Variant on L{KexGroup1 <paramiko.kex_group1.KexGroup1>} where the prime "p" and
generator "g" are provided by the server. A bit more work is required on the
client side, and a B{lot} more on the server side.
"""
from Crypto.Hash import SHA
from Crypto.Util import number
from paramiko.common import *
from paramiko import util
from paramiko.message import Message
from paramiko.ssh_exception import SSHException
_MSG_KEXDH_GEX_REQUEST_OLD, _MSG_KEXDH_GEX_GROUP, _MSG_KEXDH_GEX_INIT, \
_MSG_KEXDH_GEX_REPLY, _MSG_KEXDH_GEX_REQUEST = range(30, 35)
class KexGex (object):
name = 'diffie-hellman-group-exchange-sha1'
min_bits = 1024
max_bits = 8192
preferred_bits = 2048
def __init__(self, transport):
self.transport = transport
self.p = None
self.q = None
self.g = None
self.x = None
self.e = None
self.f = None
self.old_style = False
def start_kex(self, _test_old_style=False):
if self.transport.server_mode:
self.transport._expect_packet(_MSG_KEXDH_GEX_REQUEST, _MSG_KEXDH_GEX_REQUEST_OLD)
return
# request a bit range: we accept (min_bits) to (max_bits), but prefer
# (preferred_bits). according to the spec, we shouldn't pull the
# minimum up above 1024.
m = Message()
if _test_old_style:
# only used for unit tests: we shouldn't ever send this
m.add_byte(chr(_MSG_KEXDH_GEX_REQUEST_OLD))
m.add_int(self.preferred_bits)
self.old_style = True
else:
m.add_byte(chr(_MSG_KEXDH_GEX_REQUEST))
m.add_int(self.min_bits)
m.add_int(self.preferred_bits)
m.add_int(self.max_bits)
self.transport._send_message(m)
self.transport._expect_packet(_MSG_KEXDH_GEX_GROUP)
def parse_next(self, ptype, m):
if ptype == _MSG_KEXDH_GEX_REQUEST:
return self._parse_kexdh_gex_request(m)
elif ptype == _MSG_KEXDH_GEX_GROUP:
return self._parse_kexdh_gex_group(m)
elif ptype == _MSG_KEXDH_GEX_INIT:
return self._parse_kexdh_gex_init(m)
elif ptype == _MSG_KEXDH_GEX_REPLY:
return self._parse_kexdh_gex_reply(m)
elif ptype == _MSG_KEXDH_GEX_REQUEST_OLD:
return self._parse_kexdh_gex_request_old(m)
raise SSHException('KexGex asked to handle packet type %d' % ptype)
### internals...
def _generate_x(self):
# generate an "x" (1 < x < (p-1)/2).
q = (self.p - 1) // 2
qnorm = util.deflate_long(q, 0)
qhbyte = ord(qnorm[0])
bytes = len(qnorm)
qmask = 0xff
while not (qhbyte & 0x80):
qhbyte <<= 1
qmask >>= 1
while True:
self.transport.randpool.stir()
x_bytes = self.transport.randpool.get_bytes(bytes)
x_bytes = chr(ord(x_bytes[0]) & qmask) + x_bytes[1:]
x = util.inflate_long(x_bytes, 1)
if (x > 1) and (x < q):
break
self.x = x
def _parse_kexdh_gex_request(self, m):
minbits = m.get_int()
preferredbits = m.get_int()
maxbits = m.get_int()
# smoosh the user's preferred size into our own limits
if preferredbits > self.max_bits:
preferredbits = self.max_bits
if preferredbits < self.min_bits:
preferredbits = self.min_bits
# fix min/max if they're inconsistent. technically, we could just pout
# and hang up, but there's no harm in giving them the benefit of the
# doubt and just picking a bitsize for them.
if minbits > preferredbits:
minbits = preferredbits
if maxbits < preferredbits:
maxbits = preferredbits
# now save a copy
self.min_bits = minbits
self.preferred_bits = preferredbits
self.max_bits = maxbits
# generate prime
pack = self.transport._get_modulus_pack()
if pack is None:
raise SSHException('Can\'t do server-side gex with no modulus pack')
self.transport._log(DEBUG, 'Picking p (%d <= %d <= %d bits)' % (minbits, preferredbits, maxbits))
self.g, self.p = pack.get_modulus(minbits, preferredbits, maxbits)
m = Message()
m.add_byte(chr(_MSG_KEXDH_GEX_GROUP))
m.add_mpint(self.p)
m.add_mpint(self.g)
self.transport._send_message(m)
self.transport._expect_packet(_MSG_KEXDH_GEX_INIT)
def _parse_kexdh_gex_request_old(self, m):
# same as above, but without min_bits or max_bits (used by older clients like putty)
self.preferred_bits = m.get_int()
# smoosh the user's preferred size into our own limits
if self.preferred_bits > self.max_bits:
self.preferred_bits = self.max_bits
if self.preferred_bits < self.min_bits:
self.preferred_bits = self.min_bits
# generate prime
pack = self.transport._get_modulus_pack()
if pack is None:
raise SSHException('Can\'t do server-side gex with no modulus pack')
self.transport._log(DEBUG, 'Picking p (~ %d bits)' % (self.preferred_bits,))
self.g, self.p = pack.get_modulus(self.min_bits, self.preferred_bits, self.max_bits)
m = Message()
m.add_byte(chr(_MSG_KEXDH_GEX_GROUP))
m.add_mpint(self.p)
m.add_mpint(self.g)
self.transport._send_message(m)
self.transport._expect_packet(_MSG_KEXDH_GEX_INIT)
self.old_style = True
def _parse_kexdh_gex_group(self, m):
self.p = m.get_mpint()
self.g = m.get_mpint()
# reject if p's bit length < 1024 or > 8192
bitlen = util.bit_length(self.p)
if (bitlen < 1024) or (bitlen > 8192):
raise SSHException('Server-generated gex p (don\'t ask) is out of range (%d bits)' % bitlen)
self.transport._log(DEBUG, 'Got server p (%d bits)' % bitlen)
self._generate_x()
# now compute e = g^x mod p
self.e = pow(self.g, self.x, self.p)
m = Message()
m.add_byte(chr(_MSG_KEXDH_GEX_INIT))
m.add_mpint(self.e)
self.transport._send_message(m)
self.transport._expect_packet(_MSG_KEXDH_GEX_REPLY)
def _parse_kexdh_gex_init(self, m):
self.e = m.get_mpint()
if (self.e < 1) or (self.e > self.p - 1):
raise SSHException('Client kex "e" is out of range')
self._generate_x()
self.f = pow(self.g, self.x, self.p)
K = pow(self.e, self.x, self.p)
key = str(self.transport.get_server_key())
# okay, build up the hash H of (V_C || V_S || I_C || I_S || K_S || min || n || max || p || g || e || f || K)
hm = Message()
hm.add(self.transport.remote_version, self.transport.local_version,
self.transport.remote_kex_init, self.transport.local_kex_init,
key)
if not self.old_style:
hm.add_int(self.min_bits)
hm.add_int(self.preferred_bits)
if not self.old_style:
hm.add_int(self.max_bits)
hm.add_mpint(self.p)
hm.add_mpint(self.g)
hm.add_mpint(self.e)
hm.add_mpint(self.f)
hm.add_mpint(K)
H = SHA.new(str(hm)).digest()
self.transport._set_K_H(K, H)
# sign it
sig = self.transport.get_server_key().sign_ssh_data(self.transport.randpool, H)
# send reply
m = Message()
m.add_byte(chr(_MSG_KEXDH_GEX_REPLY))
m.add_string(key)
m.add_mpint(self.f)
m.add_string(str(sig))
self.transport._send_message(m)
self.transport._activate_outbound()
def _parse_kexdh_gex_reply(self, m):
host_key = m.get_string()
self.f = m.get_mpint()
sig = m.get_string()
if (self.f < 1) or (self.f > self.p - 1):
raise SSHException('Server kex "f" is out of range')
K = pow(self.f, self.x, self.p)
# okay, build up the hash H of (V_C || V_S || I_C || I_S || K_S || min || n || max || p || g || e || f || K)
hm = Message()
hm.add(self.transport.local_version, self.transport.remote_version,
self.transport.local_kex_init, self.transport.remote_kex_init,
host_key)
if not self.old_style:
hm.add_int(self.min_bits)
hm.add_int(self.preferred_bits)
if not self.old_style:
hm.add_int(self.max_bits)
hm.add_mpint(self.p)
hm.add_mpint(self.g)
hm.add_mpint(self.e)
hm.add_mpint(self.f)
hm.add_mpint(K)
self.transport._set_K_H(K, SHA.new(str(hm)).digest())
self.transport._verify_key(host_key, sig)
self.transport._activate_outbound()
|