plugin_e2ee.py 7.7 KB
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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# vim:fenc=utf-8 et ts=4 sts=4 sw=4
#
# Copyright © 2019 Maxime “pep” Buquet <pep@bouah.net>
#
# Distributed under terms of the zlib license. See COPYING file.

"""
    Interface for E2EE (End-to-end Encryption) plugins.
"""

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from typing import Callable, Dict, Optional, Union
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from slixmpp import InvalidJID, JID, Message
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from slixmpp.xmlstream import StanzaBase
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from poezio.tabs import ConversationTab, DynamicConversationTab, PrivateTab, MucTab
from poezio.plugin import BasePlugin

import logging
log = logging.getLogger(__name__)


ChatTabs = Union[
    MucTab,
    DynamicConversationTab,
    PrivateTab,
]

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EME_NS = 'urn:xmpp:eme:0'
EME_TAG = 'encryption'

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JCLIENT_NS = 'jabber:client'
HINTS_NS = 'urn:xmpp:hints'

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class E2EEPlugin(BasePlugin):
    """Interface for E2EE plugins"""

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    # Specifies that the encryption mechanism does more than encrypting
    # <body/>.
    stanza_encryption = False

    # Whitelist applied to messages when `stanza_encryption` is False.
    tag_whitelist = list(map(lambda x: '{%s}%s' % (x[0], x[1]), [
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        (JCLIENT_NS, 'body'),
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        (EME_NS, EME_TAG),
        (HINTS_NS, 'store'),
        (HINTS_NS, 'no-copy'),
        (HINTS_NS, 'no-store'),
        (HINTS_NS, 'no-permanent-store'),
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        # TODO: Add other encryption mechanisms tags here
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    ]))

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    replace_body_with_eme = True

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    # At least one of encryption_name and encryption_short_name must be set
    encryption_name = None  # type: Optional[str]
    encryption_short_name = None  # type: Optional[str]

    # Required.
    eme_ns = None  # type: Optional[str]

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    # Static map, to be able to limit to one encryption mechanism per tab at a
    # time
    _enabled_tabs = {}  # type: Dict[JID, Callable]

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    def init(self):
        if self.encryption_name is None and self.encryption_short_name is None:
            raise NotImplementedError

        if self.eme_ns is None:
            raise NotImplementedError

        if self.encryption_name is None:
            self.encryption_name = self.encryption_short_name
        if self.encryption_short_name is None:
            self.encryption_short_name = self.encryption_name

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        # Ensure decryption is done before everything, so that other handlers
        # don't have to know about the encryption mechanism.
        self.api.add_event_handler('muc_msg', self._decrypt, priority=0)
        self.api.add_event_handler('conversation_msg', self._decrypt, priority=0)
        self.api.add_event_handler('private_msg', self._decrypt, priority=0)

        # Ensure encryption is done after everything, so that whatever can be
        # encrypted is encrypted, and no plain element slips in.
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        # Using a stream filter might be a bit too much, but at least we're
        # sure poezio is not sneaking anything past us.
        self.core.xmpp.add_filter('out', self._encrypt)
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        for tab_t in (DynamicConversationTab, PrivateTab, MucTab):
            self.api.add_tab_command(
                tab_t,
                self.encryption_short_name,
                self._toggle_tab,
                usage='',
                short='Toggle {} encryption for tab.'.format(self.encryption_name),
                help='Toggle automatic {} encryption for tab.'.format(self.encryption_name),
            )

        ConversationTab.add_information_element(
            self.encryption_short_name,
            self._display_encryption_status,
        )
        MucTab.add_information_element(
            self.encryption_short_name,
            self._display_encryption_status,
        )
        PrivateTab.add_information_element(
            self.encryption_short_name,
            self._display_encryption_status,
        )

    def cleanup(self):
        ConversationTab.remove_information_element(self.encryption_short_name)
        MucTab.remove_information_element(self.encryption_short_name)
        PrivateTab.remove_information_element(self.encryption_short_name)

    def _display_encryption_status(self, jid_s: str) -> str:
        """
            Return information to display in the infobar if encryption is
            enabled for the JID.
        """

        try:
            jid = JID(jid_s)
        except InvalidJID:
            return ""

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        if self._encryption_enabled(jid):
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            return " " + self.encryption_short_name
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        return ""

    def _toggle_tab(self, _input: str) -> None:
        jid = self.api.current_tab().jid  # type: JID

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        if self._encryption_enabled(jid):
            del self._enabled_tabs[jid]
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            self.api.information(
                '{} encryption disabled for {}'.format(self.encryption_name, jid),
                'Info',
            )
        else:
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            self._enabled_tabs[jid] = self.encrypt
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            self.api.information(
                '{} encryption enabled for {}'.format(self.encryption_name, jid),
                'Info',
            )

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    def _encryption_enabled(self, jid: JID) -> bool:
        return jid in self._enabled_tabs and self._enabled_tabs[jid] == self.encrypt

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    def _decrypt(self, message: Message, tab: ChatTabs) -> None:
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        if message.xml.find('{%s}%s' % (EME_NS, EME_TAG)) is None:
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            return None

        if message['eme']['namespace'] != self.eme_ns:
            return None

        log.debug('Received %s message: %r', self.encryption_name, message['body'])

        self.decrypt(message, tab)

        log.debug('Decrypted %s message: %r', self.encryption_name, message['body'])
        return None

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    def _encrypt(self, stanza: StanzaBase) -> Optional[StanzaBase]:
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        if not isinstance(stanza, Message) or stanza['type'] not in ('chat', 'groupchat'):
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            return stanza
        message = stanza

        tab = self.api.current_tab()
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        jid = tab.jid
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        if not self._encryption_enabled(jid):
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            return message
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        log.debug('Sending %s message: %r', self.encryption_name, message['body'])

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        has_body = message.xml.find('{%s}%s' % (JCLIENT_NS, 'body')) is not None
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        # Drop all messages that don't contain a body if the plugin doesn't do
        # Stanza Encryption
        if not self.stanza_encryption and not has_body:
            log.debug(
                '%s plugin: Dropping message as it contains no body, and is '
                'not doesn\'t do stanza encryption: %r',
                self.encryption_name,
                message,
            )
            return None

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        # Call the enabled encrypt method
        self._enabled_tabs[jid](message, tab)
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        if has_body:
            # Only add EME tag if the message has a body.
            # Per discussion in jdev@:
            # The receiving client needs to know the message contains
            # meaningful information or not to display notifications to the
            # user, and not display anything when it's e.g., a chatstate.
            # This does leak the fact that the encrypted payload contains a
            # message.
            message['eme']['namespace'] = self.eme_ns
            message['eme']['name'] = self.encryption_name

            if self.replace_body_with_eme:
                self.core.xmpp['xep_0380'].replace_body_with_eme(message)

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        # Filter stanza with the whitelist. Plugins doing stanza encryption
        # will have to include these in their encrypted container beforehand.
        for elem in message.xml[:]:
            if elem.tag not in self.tag_whitelist:
                message.xml.remove(elem)
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        log.debug('Encrypted %s message: %r', self.encryption_name, message['body'])
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        return message
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    def decrypt(self, _message: Message, tab: ChatTabs):
        """Decryption method"""
        raise NotImplementedError

    def encrypt(self, _message: Message, tab: ChatTabs):
        """Encryption method"""
        raise NotImplementedError