gajim-otrplugin/otr.py

## Copyright (C) 2008-2012 Kjell Braden <afflux@pentabarf.de>
## Copyright (C) 2019 Pavel R. <pd at narayana dot im>
#

# This file is part of Gajim OTR Plugin.
#
# Gajim OTR Plugin is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published
# by the Free Software Foundation; version 3 only.
#
# This software is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You can always obtain full license text at <http://www.gnu.org/licenses/>.
import os
from inspect import signature
from gajim.common import const, app, helpers, configpaths
from gajim.session import ChatControlSession
from nbxmpp.protocol import Message, JID
from potr import context, crypt, proto
from .keystore import Keystore


# Prototype of OTR Channel (secure conversations between Gajim user (Alice) and Gajim peer (Bob)
class OTRChannel(context.Context):
    # this method may be called self.sendMessage() when we need to send some data to our <peer> via XMPP
    def inject(self,msg,appdata=None):
        stanza = Message(to=self.peer, body=msg.decode(), typ='chat')
        stanza.setThread(appdata or ChatControlSession.generate_thread_id(None))
        self.user.stream.send_stanza(stanza)

    # this method called on channel state change 
    def setState(self,state=0): 
        if state and state != self.state: 
            self.getCurrentTrust() is None and self.setCurrentTrust(0) != 0 and self.printl(OTR.TRUSTED[None].format(fprint=self.getCurrentKey())) # new fingerprint
            self.printl(OTR.STATUS[state].format(peer=self.peer,trust=OTR.TRUSTED[self.getCurrentTrust()],fprint=self.getCurrentKey())) # state is changed
        self.state = state
    
    # print  some text to chat window 
    def printl(self,line):
        println = self.user.getControl(self.peer) and self.user.getControl(self.peer).conv_textview.print_conversation_line
        println and println("OTR: "+line,kind='status',name='',tim='',**('jid' in signature(println).parameters and {'jid':None} or {}))

    @staticmethod 
    def getPolicy(policy): return OTR.DEFAULT_POLICY.get(policy)

# OTR instance for Gajim user (Alice)
class OTR(context.Account):
    PROTO = ('XMPP', 1024)
    ENCRYPTION_NAME = ('OTR')
    DEFAULT_POLICY = {
        'REQUIRE_ENCRYPTION': True,
        'ALLOW_V1': False,
        'ALLOW_V2': True,
        'SEND_TAG': True,
        'WHITESPACE_START_AKE': True,
        'ERROR_START_AKE': True,
    }
    TRUSTED = {None:"new fingerprint received: *{fprint}*", 0:"untrusted", 1:"trusted", 2:"authenticated"}
    STATUS = {
        context.STATE_PLAINTEXT:     "(re-)starting encrypted conversation with {peer}..",
        context.STATE_ENCRYPTED:     "{trust} encrypted conversation started (fingerprint: {fprint})", 
        context.STATE_FINISHED:      "encrypted conversation with {peer} closed (fingerprint: {fprint})",
        context.UnencryptedMessage:  "this message is *not encrypted*: {msg}",
        context.NotEncryptedError:   "unable to process message (channel lost)",
        context.ErrorReceived:       "received error message: {err}",
        crypt.InvalidParameterError: "unable to decrypt message (key/signature mismatch)",
    }

    def __init__(self,plugin,account):
        super(OTR,self).__init__(account,*OTR.PROTO)
        self.plugin = plugin
        self.log = plugin.log
        self.account = account 
        self.stream = app.connections[account]
        self.jid = self.stream.get_own_jid()
        self.keystore = Keystore(os.path.join(configpaths.get('MY_DATA'), 'otr_' + self.jid.getStripped() + '.db'))
        self.loadTrusts()

    # get chat control 
    def getControl(self,peer):
        ctl = app.interface.msg_win_mgr.get_control(peer.getStripped(),self.account)
        return ctl
        
    # get OTR context (encrypted dialog between Alice and Bob)
    def getContext(self,peer):
        peer in self.ctxs and self.ctxs[peer].state == context.STATE_FINISHED and self.ctxs.pop(peer).disconnect() # close dead channels
        self.ctxs[peer] = self.ctxs.get(peer) or OTRChannel(self,peer)
        return self.ctxs[peer]

    # load my private key
    def loadPrivkey(self):
        my = self.keystore.load(jid=self.jid)
        return (my and my.privatekey) and crypt.PK.parsePrivateKey(bytes.fromhex(my.privatekey))[0] or None
    
    # save my privatekey
    def savePrivkey(self):
        self.keystore.save(jid=self.jid,privatekey=self.getPrivkey().serializePrivateKey().hex())

    # load known fingerprints
    def loadTrusts(self):
        for peer in self.keystore.load(): self.setTrust(peer.jid,peer.fingerprint,peer.trust)
    
    # save known fingerprints
    def saveTrusts(self):
        for peer,fingerprints in self.trusts.items(): 
            for fingerprint,trust in fingerprints.items(): self.keystore.save(jid=peer,fingerprint=fingerprint,trust=trust)

    # decrypt message
    def decrypt(self,event,callback):
        peer = event.stanza.getFrom()
        channel, ctl = self.getContext(peer), self.getControl(peer)
        try:
            text, tlvs = channel.receiveMessage(event.msgtxt.encode(),appdata=event.stanza.getThread()) or b''
        except (context.UnencryptedMessage,context.NotEncryptedError,context.ErrorReceived,crypt.InvalidParameterError) as e:
            self.log.error("** got exception while decrypting message: %s" % e)
            channel.printl(OTR.STATUS[e].format(msg=event.msgtxt,err=e.args[0].error))
        else:
            event.msgtxt = text and text.decode() or ""
            event.encrypted = OTR.ENCRYPTION_NAME
            event.additional_data["encrypted"] = {"name":OTR.ENCRYPTION_NAME}
            callback(event)
        finally:
            if channel.mayRetransmit and channel.state and ctl: channel.mayRetransmit = ctl.send_message(channel.lastMessage.decode())

    # encrypt message
    def encrypt(self,event,callback):
        peer = event.msg_iq.getTo()
        channel, ctl = self.getContext(peer), event.control
        if event.xhtml: return ctl.send_message(event.message) # skip xhtml messages 
        try:
            encrypted = channel.sendMessage(context.FRAGMENT_SEND_ALL_BUT_LAST,event.message.encode(),appdata=event.msg_iq.getThread()) or b''
            message = (encrypted != self.getDefaultQueryMessage(OTR.DEFAULT_POLICY.get)) and event.message or "" 
        except context.NotEncryptedError as e:
            self.log.error("** got exception while encrypting message: %s" % e)
            channel.printl(peer,OTR.STATUS[e])
        else:
            event.msg_iq.setBody(encrypted.decode()) # encrypted data goes here 
            event.message = message  # message that will be displayed in our chat goes here
            event.encrypted, event.additional_data["encrypted"] = OTR.ENCRYPTION_NAME, {"name":OTR.ENCRYPTION_NAME} # some mandatory encryption flags
            callback(event)