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kexdhgroup14sha1.py
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kexdhgroup14sha1.py
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# Copyright (c) 2014-2015 Sam Maloney.
# License: LGPL
import llog
import asyncio
import logging
from hashlib import sha1
import dhgroup14
from sshexception import SshException
import sshtype
import packet as mnp
log = logging.getLogger(__name__)
class KexDhGroup14Sha1(object):
name = "diffie-hellman-group14-sha1"
def __init__(self, protocol):
self.dh = dhgroup14.DhGroup14()
self.protocol = protocol
@asyncio.coroutine
def run(self):
dh = self.dh
p = self.protocol
server_mode = p.server_mode
dh.generate_x()
if log.isEnabledFor(logging.DEBUG):
log.debug("x=[{}]".format(dh.x))
dh.generate_e()
if log.isEnabledFor(logging.DEBUG):
log.debug("e=[{}]".format(dh.e))
if server_mode:
pkt = yield from p.read_packet()
if not pkt:
return False
m = mnp.SshKexdhInitMessage(pkt)
if log.isEnabledFor(logging.DEBUG):
log.debug("Client sent e=[{}].".format(m.e))
self._parse_kexdh_init(m)
m = mnp.SshNewKeysMessage()
m.encode()
p.write_packet(m)
return True
# Client mode:
m = mnp.SshKexdhInitMessage()
m.e = dh.e
m.encode()
p.write_packet(m)
pkt = yield from p.read_packet()
if not pkt:
return False
m = mnp.SshKexdhReplyMessage(pkt)
r = yield from self._parse_kexdh_reply(m)
if not r:
# Client signature failed OR the client sig was valid but the id
# now verified is not wanted/allowed for connection.
return False
m = mnp.SshNewKeysMessage()
m.encode()
p.write_packet(m)
# Signal successful authentication.
return True
@asyncio.coroutine
def _parse_kexdh_reply(self, m):
# The client runs this function.
host_key = m.host_key
server_f = self.dh.f = m.f
if (server_f < 1) or (server_f > self.dh.P - 1):
raise SshException('Server kex "f" is out of range')
K = self.dh.calculate_k()
if log.isEnabledFor(logging.DEBUG):
log.debug("K=[{}].".format(K))
# H = (V_C || V_S || I_C || I_S || K_S || e || f || K).
hm = bytearray()
hm += sshtype.encodeString(self.protocol.local_banner)
hm += sshtype.encodeString(self.protocol.remote_banner)
hm += sshtype.encodeBinary(self.protocol.local_kex_init_message)
hm += sshtype.encodeBinary(self.protocol.remote_kex_init_message)
hm += sshtype.encodeBinary(host_key)
hm += sshtype.encodeMpint(self.dh.e)
hm += sshtype.encodeMpint(server_f)
hm += sshtype.encodeMpint(K)
H = sha1(hm).digest()
self.protocol.set_K_H(K, H)
log.info("Verifying signature...")
r = yield from self.protocol.verify_server_key(host_key, m.signature)
return r
def _parse_kexdh_init(self, m):
# The server runs this function.
client_e = self.dh.f = m.e
if (client_e < 1) or (client_e > self.dh.P - 1):
raise SshException("Client kex 'e' is out of range")
K = self.dh.calculate_k()
if log.isEnabledFor(logging.DEBUG):
log.debug("K=[{}].".format(K))
key = self.protocol.server_key.asbytes()
# H = (V_C || V_S || I_C || I_S || K_S || e || f || K).
hm = bytearray()
hm += sshtype.encodeString(self.protocol.remote_banner)
hm += sshtype.encodeString(self.protocol.local_banner)
hm += sshtype.encodeBinary(self.protocol.remote_kex_init_message)
hm += sshtype.encodeBinary(self.protocol.local_kex_init_message)
hm += sshtype.encodeBinary(key)
hm += sshtype.encodeMpint(client_e)
hm += sshtype.encodeMpint(self.dh.e)
hm += sshtype.encodeMpint(K)
H = sha1(hm).digest()
self.protocol.set_K_H(K, H)
# Sign it.
sig = self.protocol.server_key.sign_ssh_data(H)
# Send reply.
m = mnp.SshKexdhReplyMessage()
m.host_key = key
m.f = self.dh.e
m.signature = sig
m.encode()
self.protocol.write_packet(m)