Source Code for Module paramiko.kex_gex

  1  # Copyright (C) 2003-2007  Robey Pointer <robeypointer@gmail.com> 
  2  # 
  3  # This file is part of paramiko. 
  4  # 
  5  # Paramiko is free software; you can redistribute it and/or modify it under the 
  6  # terms of the GNU Lesser General Public License as published by the Free 
  7  # Software Foundation; either version 2.1 of the License, or (at your option) 
  8  # any later version. 
  9  # 
 10  # Paramiko is distrubuted in the hope that it will be useful, but WITHOUT ANY 
 11  # WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR 
 12  # A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more 
 13  # details. 
 14  # 
 15  # You should have received a copy of the GNU Lesser General Public License 
 16  # along with Paramiko; if not, write to the Free Software Foundation, Inc., 
 17  # 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA. 
 18   
 19  """ 
 20  Variant on L{KexGroup1 <paramiko.kex_group1.KexGroup1>} where the prime "p" and 
 21  generator "g" are provided by the server.  A bit more work is required on the 
 22  client side, and a B{lot} more on the server side. 
 23  """ 
 24   
 25  from Crypto.Hash import SHA 
 26  from Crypto.Util import number 
 27   
 28  from paramiko.common import * 
 29  from paramiko import util 
 30  from paramiko.message import Message 
 31  from paramiko.ssh_exception import SSHException 
 32   
 33   
 34  _MSG_KEXDH_GEX_REQUEST_OLD, _MSG_KEXDH_GEX_GROUP, _MSG_KEXDH_GEX_INIT, \ 
 35      _MSG_KEXDH_GEX_REPLY, _MSG_KEXDH_GEX_REQUEST = range(30, 35) 
 36   
 37   
 38 -class KexGex (object): 
 39   
 40      name = 'diffie-hellman-group-exchange-sha1' 
 41      min_bits = 1024 
 42      max_bits = 8192 
 43      preferred_bits = 2048 
 44   
 45 -    def __init__(self, transport): 
 46          self.transport = transport 
 47          self.p = None 
 48          self.q = None 
 49          self.g = None 
 50          self.x = None 
 51          self.e = None 
 52          self.f = None 
 53          self.old_style = False 
 54   
 55 -    def start_kex(self, _test_old_style=False): 
 56          if self.transport.server_mode: 
 57              self.transport._expect_packet(_MSG_KEXDH_GEX_REQUEST, _MSG_KEXDH_GEX_REQUEST_OLD) 
 58              return 
 59          # request a bit range: we accept (min_bits) to (max_bits), but prefer 
 60          # (preferred_bits).  according to the spec, we shouldn't pull the 
 61          # minimum up above 1024. 
 62          m = Message() 
 63          if _test_old_style: 
 64              # only used for unit tests: we shouldn't ever send this 
 65              m.add_byte(chr(_MSG_KEXDH_GEX_REQUEST_OLD)) 
 66              m.add_int(self.preferred_bits) 
 67              self.old_style = True 
 68          else: 
 69              m.add_byte(chr(_MSG_KEXDH_GEX_REQUEST)) 
 70              m.add_int(self.min_bits) 
 71              m.add_int(self.preferred_bits) 
 72              m.add_int(self.max_bits) 
 73          self.transport._send_message(m) 
 74          self.transport._expect_packet(_MSG_KEXDH_GEX_GROUP) 
 75   
 76 -    def parse_next(self, ptype, m): 
 77          if ptype == _MSG_KEXDH_GEX_REQUEST: 
 78              return self._parse_kexdh_gex_request(m) 
 79          elif ptype == _MSG_KEXDH_GEX_GROUP: 
 80              return self._parse_kexdh_gex_group(m) 
 81          elif ptype == _MSG_KEXDH_GEX_INIT: 
 82              return self._parse_kexdh_gex_init(m) 
 83          elif ptype == _MSG_KEXDH_GEX_REPLY: 
 84              return self._parse_kexdh_gex_reply(m) 
 85          elif ptype == _MSG_KEXDH_GEX_REQUEST_OLD: 
 86              return self._parse_kexdh_gex_request_old(m) 
 87          raise SSHException('KexGex asked to handle packet type %d' % ptype) 
 88   
 89   
 90      ###  internals... 
 91   
 92       
 93 -    def _generate_x(self): 
 94          # generate an "x" (1 < x < (p-1)/2). 
 95          q = (self.p - 1) // 2 
 96          qnorm = util.deflate_long(q, 0) 
 97          qhbyte = ord(qnorm[0]) 
 98          bytes = len(qnorm) 
 99          qmask = 0xff 
100          while not (qhbyte & 0x80): 
101              qhbyte <<= 1 
102              qmask >>= 1 
103          while True: 
104              x_bytes = self.transport.rng.read(bytes) 
105              x_bytes = chr(ord(x_bytes[0]) & qmask) + x_bytes[1:] 
106              x = util.inflate_long(x_bytes, 1) 
107              if (x > 1) and (x < q): 
108                  break 
109          self.x = x 
110   
111 -    def _parse_kexdh_gex_request(self, m): 
112          minbits = m.get_int() 
113          preferredbits = m.get_int() 
114          maxbits = m.get_int() 
115          # smoosh the user's preferred size into our own limits 
116          if preferredbits > self.max_bits: 
117              preferredbits = self.max_bits 
118          if preferredbits < self.min_bits: 
119              preferredbits = self.min_bits 
120          # fix min/max if they're inconsistent.  technically, we could just pout 
121          # and hang up, but there's no harm in giving them the benefit of the 
122          # doubt and just picking a bitsize for them. 
123          if minbits > preferredbits: 
124              minbits = preferredbits 
125          if maxbits < preferredbits: 
126              maxbits = preferredbits 
127          # now save a copy 
128          self.min_bits = minbits 
129          self.preferred_bits = preferredbits 
130          self.max_bits = maxbits 
131          # generate prime 
132          pack = self.transport._get_modulus_pack() 
133          if pack is None: 
134              raise SSHException('Can\'t do server-side gex with no modulus pack') 
135          self.transport._log(DEBUG, 'Picking p (%d <= %d <= %d bits)' % (minbits, preferredbits, maxbits)) 
136          self.g, self.p = pack.get_modulus(minbits, preferredbits, maxbits) 
137          m = Message() 
138          m.add_byte(chr(_MSG_KEXDH_GEX_GROUP)) 
139          m.add_mpint(self.p) 
140          m.add_mpint(self.g) 
141          self.transport._send_message(m) 
142          self.transport._expect_packet(_MSG_KEXDH_GEX_INIT) 
143   
144 -    def _parse_kexdh_gex_request_old(self, m): 
145          # same as above, but without min_bits or max_bits (used by older clients like putty) 
146          self.preferred_bits = m.get_int() 
147          # smoosh the user's preferred size into our own limits 
148          if self.preferred_bits > self.max_bits: 
149              self.preferred_bits = self.max_bits 
150          if self.preferred_bits < self.min_bits: 
151              self.preferred_bits = self.min_bits 
152          # generate prime 
153          pack = self.transport._get_modulus_pack() 
154          if pack is None: 
155              raise SSHException('Can\'t do server-side gex with no modulus pack') 
156          self.transport._log(DEBUG, 'Picking p (~ %d bits)' % (self.preferred_bits,)) 
157          self.g, self.p = pack.get_modulus(self.min_bits, self.preferred_bits, self.max_bits) 
158          m = Message() 
159          m.add_byte(chr(_MSG_KEXDH_GEX_GROUP)) 
160          m.add_mpint(self.p) 
161          m.add_mpint(self.g) 
162          self.transport._send_message(m) 
163          self.transport._expect_packet(_MSG_KEXDH_GEX_INIT) 
164          self.old_style = True 
165   
166 -    def _parse_kexdh_gex_group(self, m): 
167          self.p = m.get_mpint() 
168          self.g = m.get_mpint() 
169          # reject if p's bit length < 1024 or > 8192 
170          bitlen = util.bit_length(self.p) 
171          if (bitlen < 1024) or (bitlen > 8192): 
172              raise SSHException('Server-generated gex p (don\'t ask) is out of range (%d bits)' % bitlen) 
173          self.transport._log(DEBUG, 'Got server p (%d bits)' % bitlen) 
174          self._generate_x() 
175          # now compute e = g^x mod p 
176          self.e = pow(self.g, self.x, self.p) 
177          m = Message() 
178          m.add_byte(chr(_MSG_KEXDH_GEX_INIT)) 
179          m.add_mpint(self.e) 
180          self.transport._send_message(m) 
181          self.transport._expect_packet(_MSG_KEXDH_GEX_REPLY) 
182   
183 -    def _parse_kexdh_gex_init(self, m): 
184          self.e = m.get_mpint() 
185          if (self.e < 1) or (self.e > self.p - 1): 
186              raise SSHException('Client kex "e" is out of range') 
187          self._generate_x() 
188          self.f = pow(self.g, self.x, self.p) 
189          K = pow(self.e, self.x, self.p) 
190          key = str(self.transport.get_server_key()) 
191          # 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) 
192          hm = Message() 
193          hm.add(self.transport.remote_version, self.transport.local_version, 
194                 self.transport.remote_kex_init, self.transport.local_kex_init, 
195                 key) 
196          if not self.old_style: 
197              hm.add_int(self.min_bits) 
198          hm.add_int(self.preferred_bits) 
199          if not self.old_style: 
200              hm.add_int(self.max_bits) 
201          hm.add_mpint(self.p) 
202          hm.add_mpint(self.g) 
203          hm.add_mpint(self.e) 
204          hm.add_mpint(self.f) 
205          hm.add_mpint(K) 
206          H = SHA.new(str(hm)).digest() 
207          self.transport._set_K_H(K, H) 
208          # sign it 
209          sig = self.transport.get_server_key().sign_ssh_data(self.transport.rng, H) 
210          # send reply 
211          m = Message() 
212          m.add_byte(chr(_MSG_KEXDH_GEX_REPLY)) 
213          m.add_string(key) 
214          m.add_mpint(self.f) 
215          m.add_string(str(sig)) 
216          self.transport._send_message(m) 
217          self.transport._activate_outbound() 
218           
219 -    def _parse_kexdh_gex_reply(self, m): 
220          host_key = m.get_string() 
221          self.f = m.get_mpint() 
222          sig = m.get_string() 
223          if (self.f < 1) or (self.f > self.p - 1): 
224              raise SSHException('Server kex "f" is out of range') 
225          K = pow(self.f, self.x, self.p) 
226          # 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) 
227          hm = Message() 
228          hm.add(self.transport.local_version, self.transport.remote_version, 
229                 self.transport.local_kex_init, self.transport.remote_kex_init, 
230                 host_key) 
231          if not self.old_style: 
232              hm.add_int(self.min_bits) 
233          hm.add_int(self.preferred_bits) 
234          if not self.old_style: 
235              hm.add_int(self.max_bits) 
236          hm.add_mpint(self.p) 
237          hm.add_mpint(self.g) 
238          hm.add_mpint(self.e) 
239          hm.add_mpint(self.f) 
240          hm.add_mpint(K) 
241          self.transport._set_K_H(K, SHA.new(str(hm)).digest()) 
242          self.transport._verify_key(host_key, sig) 
243          self.transport._activate_outbound() 
244