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 (or correct messages, or anything more than
raw text). They will be removed and be replaced by plain text messages.

This is a limitation of the OTR protocol, and it will never be fixed. Some clients
like Pidgin-OTR try do do magic stuff with html unescaping inside the OTR body, and
it is not pretty.

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|trust|untrust]``

        This command is used to manage an OTR private session.

        - The ``start`` (or ``refresh``) command starts or refreshs a private OTR session
        - The ``end`` command ends a private OTR session
        - The ``fpr`` command gives you the fingerprint of the key of the remote entity
        - The ``ourfpr`` command gives you the fingerprint of your own key
        - The ``trust`` command marks the current remote key as trusted for the current remote JID
        - The ``untrust`` command removes that trust
        - Finally, the ``drop`` command is used if you want to delete your private key (not recoverable).

        .. warning::

            With ``drop``, the private key is only removed from the filesystem, *NOT* with multiple rewrites in a secure
            manner, you should do that yourself if you want to be sure.


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

A simple workflow looks like this:

.. 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``.

Then you use ``fpr``/``ourfpr`` to check the fingerprints, and confirm your respective
identities out-of-band.

You can then use

.. code-block:: none

    /otr trust

To set the key as trusted, which will be shown when you start or refresh a conversation
(the trust status will be in a bold font and if the key is untrusted, the remote fingerprint
will be shown).

Once you’re done, end the OTR session with

.. code-block:: none

    /otr end

Files
-----

This plugin creates trust files complatible with libotr and the files produced by gajim.


The files are located in :file:`$XDG_DATA_HOME/poezio/otr/` by default (so
:file:`~/.local/share/poezio/otr` in most cases).

Two files are created:

- An account_jid.key3 (:file:`example@example.com.key3`) file, which contains the private key
- An account_jid.fpr (:file:`example@example.com.fpr`) file, which contains the list of trusted
  (or untrusted) JIDs and keys.

Configuration
-------------

.. glossary::
    :sorted:

    keys_dir
        **Default:** ``$XDG_DATA_HOME/poezio/otr``

        The directory in which you want keys and fpr to be stored.

    allow_v2
        **Default:** ``true``

        Allow OTRv2

    allow_v1
        **Default:** ``false``

        Allow OTRv1

    log
        **Default:** false

        Log conversations (OTR start/end marker, and messages).

The :term:`allow_v1`, :term:`allow_v2` and :term:`log` configuration
parameters are tab-specific.

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

The OTR session is considered for a full jid, but the trust is considered
with a bare JID. This is important to know in the case of Private Chats, since
you cannot always get the real the JID of your contact (or check if the same
nick is used by different people).

.. _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, crypt

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 = {}
        self.trustName = safeJID(peer).bare

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

    def inject(self, msg, appdata=None):
        message = self.xmpp.make_message(mto=self.peer, mbody=msg.decode('ascii'), mtype='chat')
        message.enable('carbon_private')
        message.send()

    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:
                    if self.getCurrentTrust():
                        tab.add_message('Refreshed \x19btrusted\x19o OTR conversation with %s' % self.peer, typ=self.log)
                    else:
                        tab.add_message('Refreshed \x19buntrusted\x19o OTR conversation with %s (key: %s)' %
                                (self.peer, self.getCurrentKey()), typ=self.log)
                    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, typ=self.log)
                    hl(tab)
        else:
            if newstate == STATE_ENCRYPTED:
                if tab:
                    if self.getCurrentTrust():
                        tab.add_message('Started \x19btrusted\x19o OTR conversation with %s' % self.peer, typ=self.log)
                    else:
                        tab.add_message('Started \x19buntrusted\x19o OTR conversation with %s (key: %s)' %
                                (self.peer, self.getCurrentKey()), typ=self.log)
                    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 load_trusts(self):
        try:
            with open(self.key_dir + '.fpr', 'r') as fpr_fd:
                for line in fpr_fd:
                    ctx, acc, proto, fpr, trust = line[:-1].split('\t')

                    if acc != self.name or proto != 'xmpp':
                        continue
                    jid = safeJID(ctx).bare
                    if not jid:
                        continue
                    self.setTrust(jid, fpr, trust)
        except:
            log.error('Error in load_trusts', exc_info=True)

    def save_trusts(self):
        try:
            with open(self.key_dir + '.fpr', 'w') as fpr_fd:
                for uid, trusts in self.trusts.items():
                    for fpr, trustVal in trusts.items():
                        fpr_fd.write('\t'.join(
                                (uid, self.name, 'xmpp', fpr, trustVal)))
                        fpr_fd.write('\n')
        except:
            log.exception('Error in save_trusts', exc_info=True)

    saveTrusts = save_trusts
    loadTrusts = load_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
        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 OSError as e:
            if e.errno != 17:
                self.api.information('The OTR-specific folder could not be created'
                        ' poezio will be unable to save keys and trusts', 'OTR')

        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.account.load_trusts()
        self.contexts = {}
        usage = '[start|refresh|end|fpr|ourfpr|drop|trust|untrust]'
        shortdesc = 'Manage an OTR conversation'
        desc = ('Manage an OTR conversation.\n'
                'start/refresh: Start or refresh a conversation\n'
                'end: End a conversation\n'
                'fpr: Show the fingerprint of the key of the remote user\n'
                'ourfpr: Show the fingerprint of your own key\n'
                'drop: Remove the current key (FOREVER)\n'
                'trust: Set this key for this contact as trusted\n'
                'untrust: Remove the trust for the key of this contact\n')
        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()
            logging_policy = self.config.get_by_tabname('log', 'false', jid).lower()
            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].log = 1 if logging_policy != 'false' else 0
            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']
            del msg['html']
            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]), typ=0)
            del msg['body']
            del msg['html']
            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
            # but do an additional check because of a bug with py3k
            if ctx.state != STATE_PLAINTEXT or ctx.getPolicy('REQUIRE_ENCRYPTION'):

                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=ctx.log)
                del msg['body']
                del msg['html']
                hl(tab)
                self.core.refresh_window()
                return
            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']
            del msg['html']
            self.core.refresh_window()
            return
        except crypt.InvalidParameterError:
            tab.add_message('The message from %s could not be decrypted' %
                    msg['from'], jid=msg['from'], typ=0,
                    nick_color=theming.get_theme().COLOR_REMOTE_USER)
            hl(tab)
            del msg['body']
            del msg['html']
            self.core.refresh_window()
            return
        except:
            tab.add_message('An unspecified error in the OTR plugin occured', typ=0)
            log.error('Unspecified error in the OTR plugin', exc_info=True)
            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=ctx.log, nick_color=theming.get_theme().COLOR_REMOTE_USER)
        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'))
            tab.add_message(msg['body'],
                    nickname=self.core.own_nick or tab.own_nick,
                    nick_color=theming.get_theme().COLOR_OWN_NICK,
                    identifier=msg['id'],
                    jid=self.core.xmpp.boundjid,
                    typ=ctx.log)
            # 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':
            if name in self.contexts:
                ctx = self.contexts[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()
            tab.add_message('Private key dropped.', typ=0)
        elif arg == 'trust':
            ctx = self.get_context(name)
            key = ctx.getCurrentKey()
            if key:
                fpr = key.cfingerprint()
            else:
                return
            if not ctx.getCurrentTrust():
                ctx.setTrust(fpr, 'verified')
                self.account.saveTrusts()
                tab.add_message('You added \x19b%s\x19o with key %s to your trusted list.' % (ctx.trustName, key), typ=0)
        elif arg == 'untrust':
            ctx = self.get_context(name)
            key = ctx.getCurrentKey()
            if key:
                fpr = key.cfingerprint()
            else:
                return
            if ctx.getCurrentTrust():
                ctx.setTrust(fpr, '')
                self.account.saveTrusts()
                tab.add_message('You removed \x19b%s\x19o with key %s from your trusted list.' % (ctx.trustName, key), typ=0)
        self.core.refresh_window()

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