Question

I have error in pb, cred…

We have a simple client:

#!/usr/bin/env python

from twisted.spread import pb
from twisted.internet import reactor
from twisted.cred import credentials

def main():
    factory = pb.PBClientFactory()
    reactor.connectTCP("localhost", 8801, factory)
    def1 = factory.login(credentials.UsernamePassword("admin", "pass2"))
    def1.addCallback(connected)
    def1.addErrback(bad_connected)
    def1.addBoth(disconnect)
    reactor.run()

def bad_connected(perspective):
    print 'bad login or password', perspective
    perspective.addCallback(disconnect)

def connected(perspective):
    print "got perspective1 ref:", perspective
    print "asking it to foo(13)"

    return perspective.callRemote("foo", 13)

def disconnect(perspective):
    print 'disconnect'
    reactor.stop()

main()

If we connect -> perspective.callRemote(“foo”, 13) and Disconnect

If we no connect -> print ‘bad login or password’ and Disconnect

sever code

#!/usr/bin/env python

from zope.interface import implements
from twisted.python import failure, log
from twisted.cred import portal, checkers, credentials, error as credError
from twisted.internet import defer, reactor
from twisted.spread import pb


class PasswordDictChecker:
    implements(checkers.ICredentialsChecker)
    credentialInterfaces = (credentials.IUsernamePassword,)

    def __init__(self, passwords):
        "passwords: a dict-like object mapping usernames to passwords"
        self.passwords = passwords

    def requestAvatarId(self, credentials):
        username = credentials.username
        if self.passwords.has_key(username):
            if credentials.password == self.passwords[username]:
                return defer.succeed(username)
            else:
                return defer.fail(
                    credError.UnauthorizedLogin("Bad password"))
        else:
            return defer.fail(
                credError.UnauthorizedLogin("No such user"))

class MyRealm(object):
    implements(portal.IRealm)

    def requestAvatar(self, user, mind, *interfaces):
        assert pb.IPerspective in interfaces
        avatar = MyAvatar(user)
        avatar.attached(mind)
        return pb.IPerspective, avatar, lambda a=avatar:a.detached(mind)

class MyAvatar(pb.Avatar):
    def __init__(self, user):
        self.user = user

    def attached(self, mind):
        self.remote = mind
        print 'User %s connected' % (self.user,)

    def detached(self, mind):
        self.remote = None
        print 'User %s disconnected' % (self.user,)

passwords = {
    'admin': 'aaa',
    'user1': 'bbb',
    'user2': 'ccc'
    }

if __name__ == "__main__":
    checker = PasswordDictChecker(passwords)
    realm = MyRealm()
    p = portal.Portal(realm, [checker])

    reactor.listenTCP(8801, pb.PBServerFactory(p))
    reactor.run()

The problem is that with this writing displays an error:

Unhandled Error
Traceback (most recent call last):
Failure: twisted.cred.error.UnhandledCredentials: No checker for twisted.cred.credentials.IUsernameHashedPassword, twisted.spread.pb.IUsernameMD5Password, twisted.spread.interfaces.IJellyable

Why should he IUsernameHashedPassword?
If i change to

 credentialInterfaces = (credentials.IUsernamePassword, redentials.IUsernameHashedPassword)

Code is executed on but died on string:

if credentials.password == self.passwords[username]:

Unhandled Error
Traceback (most recent call last):
  File "C:\Python27\lib\site-packages\twisted\spread\pb.py", line 841, in _recvMessage
    netResult = object.remoteMessageReceived(self, message, netArgs, netKw)
  File "C:\Python27\lib\site-packages\twisted\spread\flavors.py", line 114, in remoteMessageReceived
    state = method(*args, **kw)
  File "C:\Python27\lib\site-packages\twisted\spread\pb.py", line 1347, in remote_respond
    d = self.portal.login(self, mind, IPerspective)
  File "C:\Python27\lib\site-packages\twisted\cred\portal.py", line 115, in login
    return maybeDeferred(self.checkers[i].requestAvatarId, credentials
--- <exception caught here> ---
  File "C:\Python27\lib\site-packages\twisted\internet\defer.py", line 133, in maybeDeferred
    result = f(*args, **kw)
  File "C:/Dropbox/my_py/network/pb-cred/pb6serverV2.py", line 21, in requestAvatarId
    if credentials.password == self.passwords[username]:
exceptions.AttributeError: _PortalAuthChallenger instance has no attribute 'password'

Please help me understand the problem.

Answer 1

You need to use a twisted.spread.pb.IUsernameMD5Password credentials object to log in, because Twisted’s PB uses a little challenge/response scheme during authentication, which requires the password to be hashed (MD5). This algorithm is currently hard-coded in the PB module. You cannot easily implement/use other credential containers with PB, unless you are planning to roll your own authentication sub-protocol.

This protocol is intended to protect client and server against man-in-the-middle attacs.

I would recommend having a look at the source code of InMemoryUsernamePasswordDatabaseDontUse for a description of how checkers are supposed to check the credentials handed to them (the name of that class is a subtle hint not to use the class in a production server…)