poezio/plugins/otr.py

"""

This plugin implements `Off The Record messaging`_.

This is a plugin used to encrypt one-to-one conversation using the OTR
encryption method. You can use it if you want good privacy, deniability,
authentication, and strong secrecy. Without this
encryption, your messages are encrypted **at least** from your client (poezio) to
your server. The message is decrypted by your server and you cannot control the
encryption method of your messages from your server to your contact’s server
(unless you are your own server’s administrator), nor from your contact’s
server to your contact’s client.

This plugin does end-to-end encryption. This means that **only** your contact can
decrypt your messages, and it is fully encrypted during **all** its travel
through the internet.

Note that if you are having an encrypted conversation with a contact, you can
**not** send XHTML-IM messages to him. They will be removed and be replaced by
plain text messages.

Installation
------------

To use the OTR plugin, you must first install pure-python-otr.

You have to install it from the git because a few issues were
found with the python3 compatibility while writing this plugin,
and the fixes did not make it into a stable release yet.

Install the python module:

.. code-block:: bash

    git clone https://github.com/afflux/pure-python-otr.git
    cd pure-python-otr
    python3 setup.py install --user

You can also use pip with the requirements.txt at the root of
the poezio directory.


Usage
-----

Command added to Conversation Tabs and Private Tabs:

.. glossary::

    /otr
        **Usage:** ``/otr [start|refresh|end|fpr|ourfpr]``

        This command is used to start (or refresh), or end an OTR private session.

        The ``fpr`` command gives you the fingerprint of the key of the remove entity, and
        the ``ourfpr`` command gives you the fingerprint of your own key.


To use OTR, make sure the plugin is loaded (if not, then do ``/load otr``).

Once you are in a private conversation, you have to do a:

.. code-block:: none

    /otr start

The status of the OTR encryption should appear in the bar between the chat and
the input as ``OTR: encrypted``.

Once you’re done, end the OTR session with

.. code-block:: none

    /otr end


Important details
-----------------

The OTR session is considered for a full jid.


.. _Off The Record messaging: http://wiki.xmpp.org/web/OTR

"""
import potr
import theming
import logging

log = logging.getLogger(__name__)
import os
import curses

from potr.context import NotEncryptedError, UnencryptedMessage, ErrorReceived, NotOTRMessage, STATE_ENCRYPTED, STATE_PLAINTEXT, STATE_FINISHED, Context, Account

from plugin import BasePlugin
from tabs import ConversationTab, DynamicConversationTab, PrivateTab
from common import safeJID
from config import config

OTR_DIR = os.path.join(os.getenv('XDG_DATA_HOME') or
        '~/.local/share', 'poezio', 'otr')

POLICY_FLAGS = {
        'ALLOW_V1':False,
        'ALLOW_V2':True,
        'REQUIRE_ENCRYPTION': False,
        'SEND_TAG': True,
        'WHITESPACE_START_AKE': True,
        'ERROR_START_AKE': True
}

log = logging.getLogger(__name__)


def hl(tab):
    if tab.state != 'current':
        tab.state = 'private'

    conv_jid = safeJID(tab.name)
    if 'private' in config.get('beep_on', 'highlight private').split():
        if config.get_by_tabname('disable_beep', 'false', conv_jid.bare, False).lower() != 'true':
            curses.beep()

class PoezioContext(Context):
    def __init__(self, account, peer, xmpp, core):
        super(PoezioContext, self).__init__(account, peer)
        self.xmpp = xmpp
        self.core = core
        self.flags = {}

    def getPolicy(self, key):
        if key in self.flags:
            return self.flags[key]
        else:
            return False

    def inject(self, msg, appdata=None):
        self.xmpp.send_message(mto=self.peer, mbody=msg.decode('ascii'), mtype='chat')

    def setState(self, newstate):
        tab = self.core.get_tab_by_name(self.peer)
        if not tab:
            tab = self.core.get_tab_by_name(safeJID(self.peer).bare, DynamicConversationTab)
            if not tab.locked_resource == safeJID(self.peer).resource:
                tab = None
        if self.state == STATE_ENCRYPTED:
            if newstate == STATE_ENCRYPTED:
                log.debug('OTR conversation with %s refreshed', self.peer)
                if tab:
                    tab.add_message('Refreshed OTR conversation with %s' % self.peer)
                    hl(tab)
            elif newstate == STATE_FINISHED or newstate == STATE_PLAINTEXT:
                log.debug('OTR conversation with %s finished', self.peer)
                if tab:
                    tab.add_message('Ended OTR conversation with %s' % self.peer)
                    hl(tab)
        else:
            if newstate == STATE_ENCRYPTED:
                if tab:
                    tab.add_message('Started OTR conversation with %s' % self.peer)
                    hl(tab)

        log.debug('Set encryption state of %s to %s', self.peer, states[newstate])
        super(PoezioContext, self).setState(newstate)
        if tab:
            self.core.refresh_window()
            self.core.doupdate()

class PoezioAccount(Account):

    def __init__(self, jid, key_dir):
        super(PoezioAccount, self).__init__(jid, 'xmpp', 1024)
        self.key_dir = os.path.join(key_dir, jid)

    def load_privkey(self):
        try:
            with open(self.key_dir + '.key3', 'rb') as keyfile:
                return potr.crypt.PK.parsePrivateKey(keyfile.read())[0]
        except:
            log.error('Error in load_privkey', exc_info=True)

    def drop_privkey(self):
        try:
            os.remove(self.key_dir + '.key3')
        except:
            log.exception('Error in drop_privkey (removing %s)', self.key_dir + '.key3')
        self.privkey = None

    def save_privkey(self):
        try:
            with open(self.key_dir + '.key3', 'xb') as keyfile:
                keyfile.write(self.getPrivkey().serializePrivateKey())
        except:
            log.error('Error in save_privkey', exc_info=True)

    def save_trusts(self):
        """TODO"""
        pass

    saveTrusts = save_trusts
    loadPrivkey = load_privkey
    savePrivkey = save_privkey

states = {
        STATE_PLAINTEXT: 'plaintext',
        STATE_ENCRYPTED: 'encrypted',
        STATE_FINISHED: 'finished',
}

class Plugin(BasePlugin):

    def init(self):
        # set the default values from the config
        policy = self.config.get('encryption_policy', 'ondemand').lower()
        POLICY_FLAGS['REQUIRE_ENCRYPTION'] = (policy == 'always')
        allow_v2 = self.config.get('allow_v2', 'true').lower()
        POLICY_FLAGS['ALLOW_V2'] = (allow_v2 != 'false')
        allow_v1 = self.config.get('allow_v1', 'false').lower()
        POLICY_FLAGS['ALLOW_v1'] = (allow_v1 == 'true')

        global OTR_DIR
        OTR_DIR = os.path.expanduser(self.config.get('keys_dir', '') or OTR_DIR)
        try:
            os.makedirs(OTR_DIR)
        except FileExistsError:
            pass
        except:
            self.api.information('The OTR-specific folder could not be created'
                    ' poezio will be unable to save keys and trusts', 'OTR')

        self.api.add_event_handler('conversation_msg', self.on_conversation_msg)
        self.api.add_event_handler('private_msg', self.on_conversation_msg)
        self.api.add_event_handler('conversation_say_after', self.on_conversation_say)
        self.api.add_event_handler('private_say_after', self.on_conversation_say)
        ConversationTab.add_information_element('otr', self.display_encryption_status)
        PrivateTab.add_information_element('otr', self.display_encryption_status)
        self.account = PoezioAccount(self.core.xmpp.boundjid.bare, OTR_DIR)
        self.contexts = {}
        usage = '[start|refresh|end|fpr|ourfpr]'
        shortdesc = 'Manage an OTR conversation'
        desc = ('Manage an OTR conversation. Use “/otr start” to start a converation,'
                ' “/otr end” to end it, “/otr fpr” to show the fingerprint of your '
                'contact, and “/otr ourfpr” to show your fingerprint.')
        self.api.add_tab_command(ConversationTab, 'otr', self.command_otr,
                help=desc,
                usage=usage,
                short=shortdesc,
                completion=self.completion_otr)
        self.api.add_tab_command(PrivateTab, 'otr', self.command_otr,
                help=desc,
                usage=usage,
                short=shortdesc,
                completion=self.completion_otr)

    def cleanup(self):
        ConversationTab.remove_information_element('otr')
        PrivateTab.remove_information_element('otr')

    def get_context(self, jid):
        jid = safeJID(jid).full
        if not jid in self.contexts:
            flags = POLICY_FLAGS.copy()
            policy = self.config.get_by_tabname('encryption_policy', 'ondemand', jid).lower()
            flags['REQUIRE_ENCRYPTION'] = (policy == 'always')
            allow_v2 = self.config.get_by_tabname('allow_v2', 'true', jid).lower()
            flags['ALLOW_V2'] = (allow_v2 != 'false')
            allow_v1 = self.config.get_by_tabname('allow_v1', 'false', jid).lower()
            flags['ALLOW_V1'] = (allow_v1 == 'true')
            self.contexts[jid] = PoezioContext(self.account, jid, self.core.xmpp, self.core)
            self.contexts[jid].flags = flags
        return self.contexts[jid]

    def on_conversation_msg(self, msg, tab):
        try:
            ctx = self.get_context(msg['from'])
            txt, tlvs = ctx.receiveMessage(msg["body"].encode('utf-8'))
        except UnencryptedMessage as err:
            # received an unencrypted message inside an OTR session
            tab.add_message('The following message from %s was not encrypted:\n%s' % (msg['from'], err.args[0].decode('utf-8')),
                    jid=msg['from'], nick_color=theming.get_theme().COLOR_REMOTE_USER,
                    typ=0)
            del msg['body']
            hl(tab)
            self.core.refresh_window()
            return
        except ErrorReceived as err:
            # Received an OTR error
            tab.add_message('Received the following error from %s: %s' % (msg['from'], err.args[0]))
            del msg['body']
            hl(tab)
            self.core.refresh_window()
            return
        except NotOTRMessage as err:
            # ignore non-otr messages
            # if we expected an OTR message, we would have
            # got an UnencryptedMesssage
            return
        except NotEncryptedError as err:
            tab.add_message('An encrypted message from %s was received but is unreadable, as you are not'
                    ' currently communicating privately.' % msg['from'],
                    jid=msg['from'], nick_color=theming.get_theme().COLOR_REMOTE_USER,
                    typ=0)
            hl(tab)
            del msg['body']
            self.core.refresh_window()
            return
        except:
            return

        # remove xhtml
        del msg['html']
        del msg['body']

        if not txt:
            return
        if isinstance(tab, PrivateTab):
            user = tab.parent_muc.get_user_by_name(msg['from'].resource)
        else:
            user = None

        body = txt.decode()
        tab.add_message(body, nickname=tab.nick, jid=msg['from'],
                forced_user=user, typ=0)
        hl(tab)
        self.core.refresh_window()
        del msg['body']

    def on_conversation_say(self, msg, tab):
        """
        On message sent
        """
        if isinstance(tab, DynamicConversationTab) and tab.locked_resource:
            name = safeJID(tab.name)
            name.resource = tab.locked_resource
            name = name.full
        else:
            name = tab.name
        ctx = self.contexts.get(name)
        if ctx and ctx.state == STATE_ENCRYPTED:
            ctx.sendMessage(0, msg['body'].encode('utf-8'))
            # remove everything from the message so that it doesn’t get sent
            del msg['body']
            del msg['replace']
            del msg['html']

    def display_encryption_status(self, jid):
        context = self.get_context(jid)
        state = states[context.state]
        return ' OTR: %s' % state

    def command_otr(self, arg):
        """
        /otr [start|refresh|end|fpr|ourfpr]
        """
        arg = arg.strip()
        tab = self.api.current_tab()
        name = tab.name
        if isinstance(tab, DynamicConversationTab) and tab.locked_resource:
            name = safeJID(tab.name)
            name.resource = tab.locked_resource
            name = name.full
        if arg == 'end': # close the session
            context = self.get_context(name)
            context.disconnect()
        elif arg == 'start' or arg == 'refresh':
            otr = self.get_context(name)
            self.core.xmpp.send_message(mto=name, mtype='chat',
                mbody=self.contexts[name].sendMessage(0, b'?OTRv?').decode())
        elif arg == 'ourfpr':
            fpr = self.account.getPrivkey()
            self.api.information('Your OTR key fingerprint is %s' % fpr, 'OTR')
        elif arg == 'fpr':
            tab = self.api.current_tab()
            if tab.get_name() in self.contexts:
                ctx = self.contexts[tab.get_name()]
                self.api.information('The key fingerprint for %s is %s' % (name, ctx.getCurrentKey()) , 'OTR')
        elif arg == 'drop':
            # drop the privkey (and obviously, end the current conversations before that)
            for context in self.contexts.values():
                if context.state not in (STATE_FINISHED, STATE_PLAINTEXT):
                    context.disconnect()
            self.account.drop_privkey()

    def completion_otr(self, the_input):
        return the_input.new_completion(['start', 'fpr', 'ourfpr', 'refresh', 'end', 'drop'], 1, quotify=True)