184 lines
6.8 KiB
Python
184 lines
6.8 KiB
Python
#!/usr/bin/python
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# variant on group1 (see kex_group1.py) where the prime "p" and generator "g"
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# are provided by the server. a bit more work is required on our side (and a
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# LOT more on the server side).
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from message import Message
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from util import inflate_long, deflate_long, generate_prime
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from secsh import SSHException
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from transport import MSG_NEWKEYS
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from Crypto.Hash import SHA
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from Crypto.Util import number
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from logging import DEBUG
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MSG_KEXDH_GEX_GROUP, MSG_KEXDH_GEX_INIT, MSG_KEXDH_GEX_REPLY, MSG_KEXDH_GEX_REQUEST = range(31, 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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def __init__(self, transport):
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self.transport = transport
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def start_kex(self):
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if self.transport.server_mode:
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self.transport.expected_packet = MSG_KEXDH_GEX_REQUEST
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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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m.add_byte(chr(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.expected_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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raise SSHException('KexGex asked to handle packet type %d' % ptype)
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def bit_length(n):
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norm = deflate_long(n, 0)
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hbyte = ord(norm[0])
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bitlen = len(norm) * 8
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while not (hbyte & 0x80):
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hbyte <<= 1
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bitlen -= 1
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return bitlen
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bit_length = staticmethod(bit_length)
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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 = deflate_long(q, 0)
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qhbyte = ord(qnorm[0])
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bytes = 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 1:
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self.transport.randpool.stir()
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x_bytes = self.transport.randpool.get_bytes(bytes)
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x_bytes = chr(ord(x_bytes[0]) & qmask) + x_bytes[1:]
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x = 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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min = m.get_int()
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preferred = m.get_int()
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max = m.get_int()
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# smoosh the user's preferred size into our own limits
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if preferred > self.max_bits:
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preferred = self.max_bits
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if preferred < self.min_bits:
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preferred = self.min_bits
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# now save a copy
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self.min_bits = min
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self.preferred_bits = preferred
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self.max_bits = max
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# generate prime
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while 1:
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# does not work FIXME
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# the problem is that it's too fscking SLOW
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self.transport.log(DEBUG, 'stir...')
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self.transport.randpool.stir()
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self.transport.log(DEBUG, 'get-prime %d...' % preferred)
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self.p = generate_prime(preferred, self.transport.randpool)
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self.transport.log(DEBUG, 'got ' + repr(self.p))
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if number.isPrime((self.p - 1) // 2):
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break
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self.g = 2
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m = Message()
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m.add_byte(chr(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.expected_packet = MSG_KEXDH_GEX_INIT
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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 = self.bit_length(self.p)
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if (bitlen < 1024) or (bitlen > 8192):
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raise SSHException('Server-generated gex p (don\'t ask) is out of range (%d bits)' % bitlen)
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self.transport.log(DEBUG, 'Got server p (%d bits)' % 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(chr(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.expected_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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K = pow(self.e, self.x, P)
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key = str(self.transport.get_server_key())
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# 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)
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hm = Message().add(self.transport.remote_version).add(self.transport.local_version)
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hm.add(self.transport.remote_kex_init).add(self.transport.local_kex_init).add(key)
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hm.add_int(self.min_bits)
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hm.add_int(self.preferred_bits)
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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(self.e).add(self.f).add(K)
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H = SHA.new(str(hm)).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(chr(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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self.transport.expected_packet = MSG_NEWKEYS
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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 (V_C || V_S || I_C || I_S || K_S || min || n || max || p || g || e || f || K)
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hm = Message().add(self.transport.local_version).add(self.transport.remote_version)
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hm.add(self.transport.local_kex_init).add(self.transport.remote_kex_init).add(host_key)
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hm.add_int(self.min_bits)
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hm.add_int(self.preferred_bits)
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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(self.e).add(self.f).add(K)
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self.transport.set_K_H(K, SHA.new(str(hm)).digest())
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self.transport.verify_key(host_key, sig)
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self.transport.activate_outbound()
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self.transport.expected_packet = MSG_NEWKEYS
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