view sat/memory/encryption.py @ 3231:e756e0eb1be4

core (memory/encryption): automatic start encryption if peer send encrypted message: If peer sends encrypted message and we have no encryption activated, we automatically start encryption to avoid sending plain text message when answering. markAsEncrypted now needs the encryption algorithm namespace as mandatory argument.
author Goffi <goffi@goffi.org>
date Mon, 23 Mar 2020 17:52:18 +0100
parents cc3fea71c365
children c161ff21ca7c
line wrap: on
line source

#!/usr/bin/env python3


# SAT: a jabber client
# Copyright (C) 2009-2020 Jérôme Poisson (goffi@goffi.org)

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This program 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 Affero General Public License for more details.

# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import copy
from functools import partial
from collections import namedtuple
from twisted.words.protocols.jabber import jid
from twisted.internet import defer
from twisted.python import failure
from sat.core.i18n import D_, _
from sat.core.constants import Const as C
from sat.core import exceptions
from sat.core.log import getLogger
from sat.tools.common import data_format
from sat.tools import utils
from sat.memory import persistent


log = getLogger(__name__)

EncryptionPlugin = namedtuple("EncryptionPlugin", ("instance",
                                                   "name",
                                                   "namespace",
                                                   "priority",
                                                   "directed"))


class EncryptionHandler:
    """Class to handle encryption sessions for a client"""
    plugins = []  # plugin able to encrypt messages

    def __init__(self, client):
        self.client = client
        self._sessions = {}  # bare_jid ==> encryption_data
        self._stored_session = persistent.PersistentDict(
            "core:encryption", profile=client.profile)

    @property
    def host(self):
        return self.client.host_app

    async def loadSessions(self):
        """Load persistent sessions"""
        await self._stored_session.load()
        start_d_list = []
        for entity_jid_s, namespace in self._stored_session.items():
            entity = jid.JID(entity_jid_s)
            start_d_list.append(defer.ensureDeferred(self.start(entity, namespace)))

        if start_d_list:
            result = await defer.DeferredList(start_d_list)
            for idx, (success, err) in enumerate(result):
                if not success:
                    entity_jid_s, namespace = list(self._stored_session.items())[idx]
                    log.warning(_(
                        "Could not restart {namespace!r} encryption with {entity}: {err}"
                        ).format(namespace=namespace, entity=entity_jid_s, err=err))
            log.info(_("encryption sessions restored"))

    @classmethod
    def registerPlugin(cls, plg_instance, name, namespace, priority=0, directed=False):
        """Register a plugin handling an encryption algorithm

        @param plg_instance(object): instance of the plugin
            it must have the following methods:
                - getTrustUI(entity): return a XMLUI for trust management
                    entity(jid.JID): entity to manage
                    The returned XMLUI must be a form
            if may have the following methods:
                - startEncryption(entity): start encrypted session
                    entity(jid.JID): entity to start encrypted session with
                - stopEncryption(entity): start encrypted session
                    entity(jid.JID): entity to stop encrypted session with
            if they don't exists, those 2 methods will be ignored.

        @param name(unicode): human readable name of the encryption algorithm
        @param namespace(unicode): namespace of the encryption algorithm
        @param priority(int): priority of this plugin to encrypt an message when not
            selected manually
        @param directed(bool): True if this plugin is directed (if it works with one
                               device only at a time)
        """
        existing_ns = set()
        existing_names = set()
        for p in cls.plugins:
            existing_ns.add(p.namespace.lower())
            existing_names.add(p.name.lower())
        if namespace.lower() in existing_ns:
            raise exceptions.ConflictError("A plugin with this namespace already exists!")
        if name.lower() in existing_names:
            raise exceptions.ConflictError("A plugin with this name already exists!")
        plugin = EncryptionPlugin(
            instance=plg_instance,
            name=name,
            namespace=namespace,
            priority=priority,
            directed=directed)
        cls.plugins.append(plugin)
        cls.plugins.sort(key=lambda p: p.priority)
        log.info(_("Encryption plugin registered: {name}").format(name=name))

    @classmethod
    def getPlugins(cls):
        return cls.plugins

    @classmethod
    def getPlugin(cls, namespace):
        try:
            return next(p for p in cls.plugins if p.namespace == namespace)
        except StopIteration:
            raise exceptions.NotFound(_(
                "Can't find requested encryption plugin: {namespace}").format(
                    namespace=namespace))

    @classmethod
    def getNamespaces(cls):
        """Get available plugin namespaces"""
        return {p.namespace for p in cls.getPlugins()}

    @classmethod
    def getNSFromName(cls, name):
        """Retrieve plugin namespace from its name

        @param name(unicode): name of the plugin (case insensitive)
        @return (unicode): namespace of the plugin
        @raise exceptions.NotFound: there is not encryption plugin of this name
        """
        for p in cls.plugins:
            if p.name.lower() == name.lower():
                return p.namespace
        raise exceptions.NotFound(_(
            "Can't find a plugin with the name \"{name}\".".format(
                name=name)))

    def getBridgeData(self, session):
        """Retrieve session data serialized for bridge.

        @param session(dict): encryption session
        @return (unicode): serialized data for bridge
        """
        if session is None:
            return ''
        plugin = session['plugin']
        bridge_data = {'name': plugin.name,
                       'namespace': plugin.namespace}
        if 'directed_devices' in session:
            bridge_data['directed_devices'] = session['directed_devices']

        return data_format.serialise(bridge_data)

    async def _startEncryption(self, plugin, entity):
        """Start encryption with a plugin

        This method must be called just before adding a plugin session.
        StartEncryptionn method of plugin will be called if it exists.
        """
        if not plugin.directed:
            await self._stored_session.aset(entity.userhost(), plugin.namespace)
        try:
            start_encryption = plugin.instance.startEncryption
        except AttributeError:
            log.debug(f"No startEncryption method found for {plugin.namespace}")
        else:
            # we copy entity to avoid having the resource changed by stop_encryption
            await utils.asDeferred(start_encryption, self.client, copy.copy(entity))

    async def _stopEncryption(self, plugin, entity):
        """Stop encryption with a plugin

        This method must be called just before removing a plugin session.
        StopEncryptionn method of plugin will be called if it exists.
        """
        try:
            await self._stored_session.adel(entity.userhost())
        except KeyError:
            pass
        try:
            stop_encryption = plugin.instance.stopEncryption
        except AttributeError:
            log.debug(f"No stopEncryption method found for {plugin.namespace}")
        else:
            # we copy entity to avoid having the resource changed by stop_encryption
            return utils.asDeferred(stop_encryption, self.client, copy.copy(entity))

    async def start(self, entity, namespace=None, replace=False):
        """Start an encryption session with an entity

        @param entity(jid.JID): entity to start an encryption session with
            must be bare jid is the algorithm encrypt for all devices
        @param namespace(unicode, None): namespace of the encryption algorithm
            to use.
            None to select automatically an algorithm
        @param replace(bool): if True and an encrypted session already exists,
            it will be replaced by the new one
        """
        if not self.plugins:
            raise exceptions.NotFound(_("No encryption plugin is registered, "
                                        "an encryption session can't be started"))

        if namespace is None:
            plugin = self.plugins[0]
        else:
            plugin = self.getPlugin(namespace)

        bare_jid = entity.userhostJID()
        if bare_jid in self._sessions:
            # we have already an encryption session with this contact
            former_plugin = self._sessions[bare_jid]["plugin"]
            if former_plugin.namespace == namespace:
                log.info(_("Session with {bare_jid} is already encrypted with {name}. "
                           "Nothing to do.").format(
                               bare_jid=bare_jid, name=former_plugin.name))
                return

            if replace:
                # there is a conflict, but replacement is requested
                # so we stop previous encryption to use new one
                del self._sessions[bare_jid]
                await self._stopEncryption(former_plugin, entity)
            else:
                msg = (_("Session with {bare_jid} is already encrypted with {name}. "
                         "Please stop encryption session before changing algorithm.")
                       .format(bare_jid=bare_jid, name=plugin.name))
                log.warning(msg)
                raise exceptions.ConflictError(msg)

        data = {"plugin": plugin}
        if plugin.directed:
            if not entity.resource:
                entity.resource = self.host.memory.getMainResource(self.client, entity)
                if not entity.resource:
                    raise exceptions.NotFound(
                        _("No resource found for {destinee}, can't encrypt with {name}")
                        .format(destinee=entity.full(), name=plugin.name))
                log.info(_("No resource specified to encrypt with {name}, using "
                           "{destinee}.").format(destinee=entity.full(),
                                                  name=plugin.name))
            # indicate that we encrypt only for some devices
            directed_devices = data['directed_devices'] = [entity.resource]
        elif entity.resource:
            raise ValueError(_("{name} encryption must be used with bare jids."))

        await self._startEncryption(plugin, entity)
        self._sessions[entity.userhostJID()] = data
        log.info(_("Encryption session has been set for {entity_jid} with "
                   "{encryption_name}").format(
                   entity_jid=entity.full(), encryption_name=plugin.name))
        self.host.bridge.messageEncryptionStarted(
            entity.full(),
            self.getBridgeData(data),
            self.client.profile)
        msg = D_("Encryption session started: your messages with {destinee} are "
                 "now end to end encrypted using {name} algorithm.").format(
                 destinee=entity.full(), name=plugin.name)
        directed_devices = data.get('directed_devices')
        if directed_devices:
            msg += "\n" + D_("Message are encrypted only for {nb_devices} device(s): "
                              "{devices_list}.").format(
                              nb_devices=len(directed_devices),
                              devices_list = ', '.join(directed_devices))

        self.client.feedback(bare_jid, msg)

    async def stop(self, entity, namespace=None):
        """Stop an encryption session with an entity

        @param entity(jid.JID): entity with who the encryption session must be stopped
            must be bare jid if the algorithm encrypt for all devices
        @param namespace(unicode): namespace of the session to stop
            when specified, used to check that we stop the right encryption session
        """
        session = self.getSession(entity.userhostJID())
        if not session:
            raise failure.Failure(
                exceptions.NotFound(_("There is no encryption session with this "
                                      "entity.")))
        plugin = session['plugin']
        if namespace is not None and plugin.namespace != namespace:
            raise exceptions.InternalError(_(
                "The encryption session is not run with the expected plugin: encrypted "
                "with {current_name} and was expecting {expected_name}").format(
                current_name=session['plugin'].namespace,
                expected_name=namespace))
        if entity.resource:
            try:
                directed_devices = session['directed_devices']
            except KeyError:
                raise exceptions.NotFound(_(
                    "There is a session for the whole entity (i.e. all devices of the "
                    "entity), not a directed one. Please use bare jid if you want to "
                    "stop the whole encryption with this entity."))

            try:
                directed_devices.remove(entity.resource)
            except ValueError:
                raise exceptions.NotFound(_("There is no directed session with this "
                                            "entity."))
            else:
                if not directed_devices:
                    # if we have no more directed device sessions,
                    # we stop the whole session
                    # see comment below for deleting session before stopping encryption
                    del self._sessions[entity.userhostJID()]
                    await self._stopEncryption(plugin, entity)
        else:
            # plugin's stopEncryption may call stop again (that's the case with OTR)
            # so we need to remove plugin from session before calling self._stopEncryption
            del self._sessions[entity.userhostJID()]
            await self._stopEncryption(plugin, entity)

        log.info(_("encryption session stopped with entity {entity}").format(
            entity=entity.full()))
        self.host.bridge.messageEncryptionStopped(
            entity.full(),
            {'name': plugin.name,
             'namespace': plugin.namespace,
            },
            self.client.profile)
        msg = D_("Encryption session finished: your messages with {destinee} are "
                 "NOT end to end encrypted anymore.\nYour server administrators or "
                 "{destinee} server administrators will be able to read them.").format(
                 destinee=entity.full())

        self.client.feedback(entity, msg)

    def getSession(self, entity):
        """Get encryption session for this contact

        @param entity(jid.JID): get the session for this entity
            must be a bare jid
        @return (dict, None): encryption session data
            None if there is not encryption for this session with this jid
        """
        if entity.resource:
            raise ValueError("Full jid given when expecting bare jid")
        return self._sessions.get(entity)

    def getTrustUI(self, entity_jid, namespace=None):
        """Retrieve encryption UI

        @param entity_jid(jid.JID): get the UI for this entity
            must be a bare jid
        @param namespace(unicode): namespace of the algorithm to manage
            if None use current algorithm
        @return D(xmlui): XMLUI for trust management
            the xmlui is a form
            None if there is not encryption for this session with this jid
        @raise exceptions.NotFound: no algorithm/plugin found
        @raise NotImplementedError: plugin doesn't handle UI management
        """
        if namespace is None:
            session = self.getSession(entity_jid)
            if not session:
                raise exceptions.NotFound(
                    "No encryption session currently active for {entity_jid}"
                    .format(entity_jid=entity_jid.full()))
            plugin = session['plugin']
        else:
            plugin = self.getPlugin(namespace)
        try:
            get_trust_ui = plugin.instance.getTrustUI
        except AttributeError:
            raise NotImplementedError(
                "Encryption plugin doesn't handle trust management UI")
        else:
            return defer.maybeDeferred(get_trust_ui, self.client, entity_jid)

    ## Menus ##

    @classmethod
    def _importMenus(cls, host):
        host.importMenu(
             (D_("Encryption"), D_("unencrypted (plain text)")),
             partial(cls._onMenuUnencrypted, host=host),
             security_limit=0,
             help_string=D_("End encrypted session"),
             type_=C.MENU_SINGLE,
        )
        for plg in cls.getPlugins():
            host.importMenu(
                 (D_("Encryption"), plg.name),
                 partial(cls._onMenuName, host=host, plg=plg),
                 security_limit=0,
                 help_string=D_("Start {name} session").format(name=plg.name),
                 type_=C.MENU_SINGLE,
            )
            host.importMenu(
                 (D_("Encryption"), D_("⛨ {name} trust").format(name=plg.name)),
                 partial(cls._onMenuTrust, host=host, plg=plg),
                 security_limit=0,
                 help_string=D_("Manage {name} trust").format(name=plg.name),
                 type_=C.MENU_SINGLE,
            )

    @classmethod
    def _onMenuUnencrypted(cls, data, host, profile):
        client = host.getClient(profile)
        peer_jid = jid.JID(data['jid']).userhostJID()
        d = defer.ensureDeferred(client.encryption.stop(peer_jid))
        d.addCallback(lambda __: {})
        return d

    @classmethod
    def _onMenuName(cls, data, host, plg, profile):
        client = host.getClient(profile)
        peer_jid = jid.JID(data['jid'])
        if not plg.directed:
            peer_jid = peer_jid.userhostJID()
        d = defer.ensureDeferred(
            client.encryption.start(peer_jid, plg.namespace, replace=True))
        d.addCallback(lambda __: {})
        return d

    @classmethod
    @defer.inlineCallbacks
    def _onMenuTrust(cls, data, host, plg, profile):
        client = host.getClient(profile)
        peer_jid = jid.JID(data['jid']).userhostJID()
        ui = yield client.encryption.getTrustUI(peer_jid, plg.namespace)
        defer.returnValue({'xmlui': ui.toXml()})

    ## Triggers ##

    def setEncryptionFlag(self, mess_data):
        """Set "encryption" key in mess_data if session with destinee is encrypted"""
        to_jid = mess_data['to']
        encryption = self._sessions.get(to_jid.userhostJID())
        if encryption is not None:
            plugin = encryption['plugin']
            if mess_data["type"] == "groupchat" and plugin.directed:
                raise exceptions.InternalError(
                f"encryption flag must not be set for groupchat if encryption algorithm "
                f"({encryption['plugin'].name}) is directed!")
            mess_data[C.MESS_KEY_ENCRYPTION] = encryption
            self.markAsEncrypted(mess_data, plugin.namespace)

    ## Misc ##

    def markAsEncrypted(self, mess_data, namespace):
        """Helper method to mark a message as having been e2e encrypted.

        This should be used in the post_treat workflow of messageReceived trigger of
        the plugin
        @param mess_data(dict): message data as used in post treat workflow
        @param namespace(str): namespace of the algorithm used for encrypting the message
        """
        mess_data['extra'][C.MESS_KEY_ENCRYPTED] = True
        from_bare_jid = mess_data['from'].userhostJID()
        if from_bare_jid != self.client.jid.userhostJID():
            session = self.getSession(from_bare_jid)
            if session is None:
                # if we are currently unencrypted, we start a session automatically
                # to avoid sending unencrypted messages in an encrypted context
                log.info(_(
                    "Starting e2e session with {peer_jid} as we receive encrypted "
                    "messages")
                    .format(peer_jid=from_bare_jid)
                )
                defer.ensureDeferred(self.start(from_bare_jid, namespace))

        return mess_data

    def isEncryptionRequested(self, mess_data, namespace=None):
        """Helper method to check if encryption is requested in an outgoind message

        @param mess_data(dict): message data for outgoing message
        @param namespace(str, None): if set, check if encryption is requested for the
            algorithm specified
        @return (bool): True if the encryption flag is present
        """
        encryption = mess_data.get(C.MESS_KEY_ENCRYPTION)
        if encryption is None:
            return False
        # we get plugin even if namespace is None to be sure that the key exists
        plugin = encryption['plugin']
        if namespace is None:
            return True
        return plugin.namespace == namespace

    def isEncrypted(self, mess_data):
        """Helper method to check if a message has the e2e encrypted flag

        @param mess_data(dict): message data
        @return (bool): True if the encrypted flag is present
        """
        return mess_data['extra'].get(C.MESS_KEY_ENCRYPTED, False)


    def markAsTrusted(self, mess_data):
        """Helper methor to mark a message as sent from a trusted entity.

        This should be used in the post_treat workflow of messageReceived trigger of
        the plugin
        @param mess_data(dict): message data as used in post treat workflow
        """
        mess_data[C.MESS_KEY_TRUSTED] = True
        return mess_data

    def markAsUntrusted(self, mess_data):
        """Helper methor to mark a message as sent from an untrusted entity.

        This should be used in the post_treat workflow of messageReceived trigger of
        the plugin
        @param mess_data(dict): message data as used in post treat workflow
        """
        mess_data['trusted'] = False
        return mess_data