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# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
A Factory for SSH servers.
See also L{twisted.conch.openssh_compat.factory} for OpenSSH compatibility.
Maintainer: Paul Swartz
"""
from __future__ import division, absolute_import
from twisted.internet import protocol
from twisted.python import log
from twisted.conch import error
from twisted.conch.ssh import (_kex, transport, userauth, connection)
import random
class SSHFactory(protocol.Factory):
"""
A Factory for SSH servers.
"""
protocol = transport.SSHServerTransport
services = {
b'ssh-userauth':userauth.SSHUserAuthServer,
b'ssh-connection':connection.SSHConnection
}
def startFactory(self):
"""
Check for public and private keys.
"""
if not hasattr(self,'publicKeys'):
self.publicKeys = self.getPublicKeys()
if not hasattr(self,'privateKeys'):
self.privateKeys = self.getPrivateKeys()
if not self.publicKeys or not self.privateKeys:
raise error.ConchError('no host keys, failing')
if not hasattr(self,'primes'):
self.primes = self.getPrimes()
def buildProtocol(self, addr):
"""
Create an instance of the server side of the SSH protocol.
@type addr: L{twisted.internet.interfaces.IAddress} provider
@param addr: The address at which the server will listen.
@rtype: L{twisted.conch.ssh.transport.SSHServerTransport}
@return: The built transport.
"""
t = protocol.Factory.buildProtocol(self, addr)
t.supportedPublicKeys = self.privateKeys.keys()
if not self.primes:
log.msg('disabling non-fixed-group key exchange algorithms '
'because we cannot find moduli file')
t.supportedKeyExchanges = [
kexAlgorithm for kexAlgorithm in t.supportedKeyExchanges
if _kex.isFixedGroup(kexAlgorithm) or
_kex.isEllipticCurve(kexAlgorithm)]
return t
def getPublicKeys(self):
"""
Called when the factory is started to get the public portions of the
servers host keys. Returns a dictionary mapping SSH key types to
public key strings.
@rtype: L{dict}
"""
raise NotImplementedError('getPublicKeys unimplemented')
def getPrivateKeys(self):
"""
Called when the factory is started to get the private portions of the
servers host keys. Returns a dictionary mapping SSH key types to
L{twisted.conch.ssh.keys.Key} objects.
@rtype: L{dict}
"""
raise NotImplementedError('getPrivateKeys unimplemented')
def getPrimes(self):
"""
Called when the factory is started to get Diffie-Hellman generators and
primes to use. Returns a dictionary mapping number of bits to lists
of tuple of (generator, prime).
@rtype: L{dict}
"""
def getDHPrime(self, bits):
"""
Return a tuple of (g, p) for a Diffe-Hellman process, with p being as
close to bits bits as possible.
@type bits: L{int}
@rtype: L{tuple}
"""
primesKeys = sorted(self.primes.keys(), key=lambda i: abs(i - bits))
realBits = primesKeys[0]
return random.choice(self.primes[realBits])
def getService(self, transport, service):
"""
Return a class to use as a service for the given transport.
@type transport: L{transport.SSHServerTransport}
@type service: L{bytes}
@rtype: subclass of L{service.SSHService}
"""
if service == b'ssh-userauth' or hasattr(transport, 'avatar'):
return self.services[service]
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