paramiko.kex

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() -

Source Code for Module paramiko.kex_gex