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288 lines
10 KiB
Python
288 lines
10 KiB
Python
# Copyright (C) 2003-2007 Robey Pointer <robeypointer@gmail.com>
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#
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# This file is part of paramiko.
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#
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# Paramiko is free software; you can redistribute it and/or modify it under the
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# terms of the GNU Lesser General Public License as published by the Free
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# Software Foundation; either version 2.1 of the License, or (at your option)
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# any later version.
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#
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# Paramiko is distributed in the hope that it will be useful, but WITHOUT ANY
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# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
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# A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
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# details.
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#
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# You should have received a copy of the GNU Lesser General Public License
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# along with Paramiko; if not, write to the Free Software Foundation, Inc.,
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# 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
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"""
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Variant on `KexGroup1 <paramiko.kex_group1.KexGroup1>` where the prime "p" and
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generator "g" are provided by the server. A bit more work is required on the
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client side, and a **lot** more on the server side.
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"""
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import os
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from hashlib import sha1, sha256
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from paramiko import util
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from paramiko.common import DEBUG
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from paramiko.message import Message
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from paramiko.py3compat import byte_chr, byte_ord, byte_mask
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from paramiko.ssh_exception import SSHException
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(
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_MSG_KEXDH_GEX_REQUEST_OLD,
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_MSG_KEXDH_GEX_GROUP,
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_MSG_KEXDH_GEX_INIT,
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_MSG_KEXDH_GEX_REPLY,
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_MSG_KEXDH_GEX_REQUEST,
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) = range(30, 35)
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(
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c_MSG_KEXDH_GEX_REQUEST_OLD,
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c_MSG_KEXDH_GEX_GROUP,
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c_MSG_KEXDH_GEX_INIT,
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c_MSG_KEXDH_GEX_REPLY,
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c_MSG_KEXDH_GEX_REQUEST,
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) = [byte_chr(c) for c in range(30, 35)]
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class KexGex(object):
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name = "diffie-hellman-group-exchange-sha1"
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min_bits = 1024
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max_bits = 8192
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preferred_bits = 2048
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hash_algo = sha1
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def __init__(self, transport):
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self.transport = transport
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self.p = None
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self.q = None
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self.g = None
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self.x = None
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self.e = None
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self.f = None
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self.old_style = False
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def start_kex(self, _test_old_style=False):
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if self.transport.server_mode:
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self.transport._expect_packet(
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_MSG_KEXDH_GEX_REQUEST, _MSG_KEXDH_GEX_REQUEST_OLD
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)
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return
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# request a bit range: we accept (min_bits) to (max_bits), but prefer
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# (preferred_bits). according to the spec, we shouldn't pull the
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# minimum up above 1024.
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m = Message()
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if _test_old_style:
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# only used for unit tests: we shouldn't ever send this
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m.add_byte(c_MSG_KEXDH_GEX_REQUEST_OLD)
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m.add_int(self.preferred_bits)
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self.old_style = True
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else:
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m.add_byte(c_MSG_KEXDH_GEX_REQUEST)
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m.add_int(self.min_bits)
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m.add_int(self.preferred_bits)
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m.add_int(self.max_bits)
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self.transport._send_message(m)
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self.transport._expect_packet(_MSG_KEXDH_GEX_GROUP)
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def parse_next(self, ptype, m):
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if ptype == _MSG_KEXDH_GEX_REQUEST:
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return self._parse_kexdh_gex_request(m)
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elif ptype == _MSG_KEXDH_GEX_GROUP:
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return self._parse_kexdh_gex_group(m)
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elif ptype == _MSG_KEXDH_GEX_INIT:
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return self._parse_kexdh_gex_init(m)
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elif ptype == _MSG_KEXDH_GEX_REPLY:
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return self._parse_kexdh_gex_reply(m)
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elif ptype == _MSG_KEXDH_GEX_REQUEST_OLD:
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return self._parse_kexdh_gex_request_old(m)
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msg = "KexGex {} asked to handle packet type {:d}"
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raise SSHException(msg.format(self.name, ptype))
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# ...internals...
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def _generate_x(self):
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# generate an "x" (1 < x < (p-1)/2).
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q = (self.p - 1) // 2
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qnorm = util.deflate_long(q, 0)
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qhbyte = byte_ord(qnorm[0])
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byte_count = len(qnorm)
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qmask = 0xff
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while not (qhbyte & 0x80):
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qhbyte <<= 1
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qmask >>= 1
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while True:
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x_bytes = os.urandom(byte_count)
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x_bytes = byte_mask(x_bytes[0], qmask) + x_bytes[1:]
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x = util.inflate_long(x_bytes, 1)
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if (x > 1) and (x < q):
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break
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self.x = x
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def _parse_kexdh_gex_request(self, m):
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minbits = m.get_int()
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preferredbits = m.get_int()
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maxbits = m.get_int()
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# smoosh the user's preferred size into our own limits
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if preferredbits > self.max_bits:
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preferredbits = self.max_bits
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if preferredbits < self.min_bits:
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preferredbits = self.min_bits
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# fix min/max if they're inconsistent. technically, we could just pout
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# and hang up, but there's no harm in giving them the benefit of the
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# doubt and just picking a bitsize for them.
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if minbits > preferredbits:
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minbits = preferredbits
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if maxbits < preferredbits:
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maxbits = preferredbits
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# now save a copy
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self.min_bits = minbits
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self.preferred_bits = preferredbits
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self.max_bits = maxbits
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# generate prime
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pack = self.transport._get_modulus_pack()
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if pack is None:
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raise SSHException("Can't do server-side gex with no modulus pack")
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self.transport._log(
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DEBUG,
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"Picking p ({} <= {} <= {} bits)".format(
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minbits, preferredbits, maxbits
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),
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)
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self.g, self.p = pack.get_modulus(minbits, preferredbits, maxbits)
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m = Message()
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m.add_byte(c_MSG_KEXDH_GEX_GROUP)
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m.add_mpint(self.p)
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m.add_mpint(self.g)
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self.transport._send_message(m)
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self.transport._expect_packet(_MSG_KEXDH_GEX_INIT)
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def _parse_kexdh_gex_request_old(self, m):
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# same as above, but without min_bits or max_bits (used by older
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# clients like putty)
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self.preferred_bits = m.get_int()
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# smoosh the user's preferred size into our own limits
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if self.preferred_bits > self.max_bits:
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self.preferred_bits = self.max_bits
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if self.preferred_bits < self.min_bits:
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self.preferred_bits = self.min_bits
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# generate prime
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pack = self.transport._get_modulus_pack()
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if pack is None:
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raise SSHException("Can't do server-side gex with no modulus pack")
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self.transport._log(
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DEBUG, "Picking p (~ {} bits)".format(self.preferred_bits)
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)
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self.g, self.p = pack.get_modulus(
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self.min_bits, self.preferred_bits, self.max_bits
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)
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m = Message()
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m.add_byte(c_MSG_KEXDH_GEX_GROUP)
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m.add_mpint(self.p)
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m.add_mpint(self.g)
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self.transport._send_message(m)
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self.transport._expect_packet(_MSG_KEXDH_GEX_INIT)
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self.old_style = True
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def _parse_kexdh_gex_group(self, m):
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self.p = m.get_mpint()
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self.g = m.get_mpint()
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# reject if p's bit length < 1024 or > 8192
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bitlen = util.bit_length(self.p)
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if (bitlen < 1024) or (bitlen > 8192):
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raise SSHException(
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"Server-generated gex p (don't ask) is out of range "
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"({} bits)".format(bitlen)
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)
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self.transport._log(DEBUG, "Got server p ({} bits)".format(bitlen))
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self._generate_x()
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# now compute e = g^x mod p
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self.e = pow(self.g, self.x, self.p)
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m = Message()
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m.add_byte(c_MSG_KEXDH_GEX_INIT)
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m.add_mpint(self.e)
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self.transport._send_message(m)
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self.transport._expect_packet(_MSG_KEXDH_GEX_REPLY)
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def _parse_kexdh_gex_init(self, m):
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self.e = m.get_mpint()
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if (self.e < 1) or (self.e > self.p - 1):
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raise SSHException('Client kex "e" is out of range')
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self._generate_x()
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self.f = pow(self.g, self.x, self.p)
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K = pow(self.e, self.x, self.p)
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key = self.transport.get_server_key().asbytes()
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# okay, build up the hash H of
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# (V_C || V_S || I_C || I_S || K_S || min || n || max || p || g || e || f || K) # noqa
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hm = Message()
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hm.add(
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self.transport.remote_version,
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self.transport.local_version,
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self.transport.remote_kex_init,
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self.transport.local_kex_init,
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key,
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)
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if not self.old_style:
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hm.add_int(self.min_bits)
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hm.add_int(self.preferred_bits)
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if not self.old_style:
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hm.add_int(self.max_bits)
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hm.add_mpint(self.p)
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hm.add_mpint(self.g)
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hm.add_mpint(self.e)
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hm.add_mpint(self.f)
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hm.add_mpint(K)
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H = self.hash_algo(hm.asbytes()).digest()
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self.transport._set_K_H(K, H)
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# sign it
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sig = self.transport.get_server_key().sign_ssh_data(H)
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# send reply
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m = Message()
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m.add_byte(c_MSG_KEXDH_GEX_REPLY)
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m.add_string(key)
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m.add_mpint(self.f)
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m.add_string(sig)
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self.transport._send_message(m)
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self.transport._activate_outbound()
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def _parse_kexdh_gex_reply(self, m):
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host_key = m.get_string()
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self.f = m.get_mpint()
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sig = m.get_string()
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if (self.f < 1) or (self.f > self.p - 1):
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raise SSHException('Server kex "f" is out of range')
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K = pow(self.f, self.x, self.p)
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# okay, build up the hash H of
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# (V_C || V_S || I_C || I_S || K_S || min || n || max || p || g || e || f || K) # noqa
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hm = Message()
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hm.add(
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self.transport.local_version,
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self.transport.remote_version,
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self.transport.local_kex_init,
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self.transport.remote_kex_init,
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host_key,
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)
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if not self.old_style:
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hm.add_int(self.min_bits)
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hm.add_int(self.preferred_bits)
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if not self.old_style:
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hm.add_int(self.max_bits)
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hm.add_mpint(self.p)
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hm.add_mpint(self.g)
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hm.add_mpint(self.e)
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hm.add_mpint(self.f)
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hm.add_mpint(K)
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self.transport._set_K_H(K, self.hash_algo(hm.asbytes()).digest())
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self.transport._verify_key(host_key, sig)
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self.transport._activate_outbound()
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class KexGexSHA256(KexGex):
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name = "diffie-hellman-group-exchange-sha256"
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hash_algo = sha256
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