[project @ Arch-1:robey@lag.net--2003-public%secsh--dev--1.0--base-0]

initial import

(automatically generated log message)

1 files changed, 180 insertions, 0 deletions

diff --git a/kex_gex.py b/kex_gex.py
new file mode 100644
index 00000000..01e74f2b
--- /dev/null
+++ b/kex_gex.py
@@ -0,0 +1,180 @@
+#!/usr/bin/python
+
+# variant on group1 (see kex_group1.py) where the prime "p" and generator "g"
+# are provided by the server.  a bit more work is required on our side (and a
+# LOT more on the server side).
+
+from message import Message, inflate_long, deflate_long
+from secsh import SSHException
+from transport import MSG_NEWKEYS
+from Crypto.Hash import SHA
+from Crypto.Util import number
+from logging import DEBUG
+
+MSG_KEXDH_GEX_GROUP, MSG_KEXDH_GEX_INIT, MSG_KEXDH_GEX_REPLY, MSG_KEXDH_GEX_REQUEST = range(31, 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
+
+    def start_kex(self):
+        if self.transport.server_mode:
+            self.transport.expected_packet = MSG_KEXDH_GEX_REQUEST
+            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()
+        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.expected_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)
+        raise SSHException('KexGex asked to handle packet type %d' % ptype)
+
+    def bit_length(n):
+        norm = deflate_long(n, 0)
+        hbyte = ord(norm[0])
+        bitlen = len(norm) * 8
+        while not (hbyte & 0x80):
+            hbyte <<= 1
+            bitlen -= 1
+        return bitlen
+    bit_length = staticmethod(bit_length)
+
+    def generate_x(self):
+        # generate an "x" (1 < x < (p-1)/2).
+        q = (self.p - 1) // 2
+        qnorm = deflate_long(q, 0)
+        qhbyte = ord(qnorm[0])
+        bytes = len(qnorm)
+        qmask = 0xff
+        while not (qhbyte & 0x80):
+            qhbyte <<= 1
+            qmask >>= 1
+        while 1:
+            self.transport.randpool.stir()
+            x_bytes = self.transport.randpool.get_bytes(bytes)
+            x_bytes = chr(ord(x_bytes[0]) & qmask) + x_bytes[1:]
+            x = inflate_long(x_bytes, 1)
+            if (x > 1) and (x < q):
+                break
+        self.x = x
+
+    def parse_kexdh_gex_request(self, m):
+        min = m.get_int()
+        preferred = m.get_int()
+        max = m.get_int()
+        # smoosh the user's preferred size into our own limits
+        if preferred > self.max_bits:
+            preferred = self.max_bits
+        if preferred < self.min_bits:
+            preferred = self.min_bits
+        # now save a copy
+        self.min_bits = min
+        self.preferred_bits = preferred
+        self.max_bits = max
+        # generate prime
+        while 1:
+            self.transport.log(DEBUG, 'stir...')
+            self.transport.randpool.stir()
+            self.transport.log(DEBUG, 'get-prime %d...' % preferred)
+            self.p = number.getRandomNumber(preferred, self.transport.randpool.get_bytes)
+            self.transport.log(DEBUG, 'got ' + repr(self.p))
+            if number.isPrime((self.p - 1) // 2):
+                break
+        self.g = 2
+        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.expected_packet = MSG_KEXDH_GEX_INIT
+
+    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 = self.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.expected_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()
+        K = pow(self.e, self.x, 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().add(self.transport.remote_version).add(self.transport.local_version)
+        hm.add(self.transport.remote_kex_init).add(self.transport.local_kex_init).add(key)
+        hm.add_int(self.min_bits)
+        hm.add_int(self.preferred_bits)
+        hm.add_int(self.max_bits)
+        hm.add_mpint(self.p)
+        hm.add_mpint(self.g)
+        hm.add(self.e).add(self.f).add(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(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(sig)
+        self.transport.send_message(m)
+        self.transport.activate_outbound()
+        self.transport.expected_packet = MSG_NEWKEYS
+        
+    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().add(self.transport.local_version).add(self.transport.remote_version)
+        hm.add(self.transport.local_kex_init).add(self.transport.remote_kex_init).add(host_key)
+        hm.add_int(self.min_bits)
+        hm.add_int(self.preferred_bits)
+        hm.add_int(self.max_bits)
+        hm.add_mpint(self.p)
+        hm.add_mpint(self.g)
+        hm.add(self.e).add(self.f).add(K)
+        self.transport.set_K_H(K, SHA.new(str(hm)).digest())
+        self.transport.verify_key(host_key, sig)
+        self.transport.activate_outbound()
+        self.transport.expected_packet = MSG_NEWKEYS
+
+