gajim-otrplugin/potr/context.py

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# Copyright 2011-2012 Kjell Braden <afflux@pentabarf.de>
#
# This file is part of the python-potr library.
#
# python-potr is free software; you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# any later version.
#
# python-potr 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 Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this library. If not, see <http://www.gnu.org/licenses/>.
# some python3 compatibilty
from __future__ import unicode_literals
try:
type(basestring)
except NameError:
# all strings are unicode in python3k
basestring = str
unicode = str
# callable is not available in python 3.0 and 3.1
try:
type(callable)
except NameError:
from collections import Callable
def callable(x):
return isinstance(x, Callable)
import base64
import logging
import struct
logger = logging.getLogger(__name__)
from potr import crypt
from potr import proto
from potr import compatcrypto
from time import time
EXC_UNREADABLE_MESSAGE = 1
EXC_FINISHED = 2
HEARTBEAT_INTERVAL = 60
STATE_PLAINTEXT = 0
STATE_ENCRYPTED = 1
STATE_FINISHED = 2
FRAGMENT_SEND_ALL = 0
FRAGMENT_SEND_ALL_BUT_FIRST = 1
FRAGMENT_SEND_ALL_BUT_LAST = 2
OFFER_NOTSENT = 0
OFFER_SENT = 1
OFFER_REJECTED = 2
OFFER_ACCEPTED = 3
class Context(object):
def __init__(self, account, peername):
self.user = account
self.peer = peername
self.policy = {}
self.crypto = crypt.CryptEngine(self)
self.tagOffer = OFFER_NOTSENT
self.mayRetransmit = 0
self.lastSend = 0
self.lastMessage = None
self.state = STATE_PLAINTEXT
self.trustName = self.peer
self.fragmentInfo = None
self.fragment = None
self.discardFragment()
def getPolicy(self, key):
raise NotImplementedError
def inject(self, msg, appdata=None):
raise NotImplementedError
def policyOtrEnabled(self):
return self.getPolicy('ALLOW_V2') or self.getPolicy('ALLOW_V1')
def discardFragment(self):
self.fragmentInfo = (0, 0)
self.fragment = []
def fragmentAccumulate(self, message):
'''Accumulate a fragmented message. Returns None if the fragment is
to be ignored, returns a string if the message is ready for further
processing'''
params = message.split(b',')
if len(params) < 5 or not params[1].isdigit() or not params[2].isdigit():
logger.warning('invalid formed fragmented message: %r', params)
self.discardFragment()
return message
K, N = self.fragmentInfo
try:
k = int(params[1])
n = int(params[2])
except ValueError:
logger.warning('invalid formed fragmented message: %r', params)
self.discardFragment()
return message
fragData = params[3]
logger.debug(params)
if n >= k == 1:
# first fragment
self.discardFragment()
self.fragmentInfo = (k, n)
self.fragment.append(fragData)
elif N == n >= k > 1 and k == K+1:
# accumulate
self.fragmentInfo = (k, n)
self.fragment.append(fragData)
else:
# bad, discard
self.discardFragment()
logger.warning('invalid fragmented message: %r', params)
return message
if n == k > 0:
assembled = b''.join(self.fragment)
self.discardFragment()
return assembled
return None
def removeFingerprint(self, fingerprint):
self.user.removeFingerprint(self.trustName, fingerprint)
def setTrust(self, fingerprint, trustLevel):
''' sets the trust level for the given fingerprint.
trust is usually:
- the empty string for known but untrusted keys
- 'verified' for manually verified keys
- 'smp' for smp-style verified keys '''
self.user.setTrust(self.trustName, fingerprint, trustLevel)
def getTrust(self, fingerprint, default=None):
return self.user.getTrust(self.trustName, fingerprint, default)
def setCurrentTrust(self, trustLevel):
self.setTrust(self.crypto.theirPubkey.cfingerprint(), trustLevel)
def getCurrentKey(self):
return self.crypto.theirPubkey
def getCurrentTrust(self):
''' returns a 2-tuple: first element is the current fingerprint,
second is:
- None if the key is unknown yet
- a non-empty string if the key is trusted
- an empty string if the key is untrusted '''
if self.crypto.theirPubkey is None:
return None
return self.getTrust(self.crypto.theirPubkey.cfingerprint(), None)
def receiveMessage(self, messageData, appdata=None):
IGN = None, []
if not self.policyOtrEnabled():
raise NotOTRMessage(messageData)
message = self.parse(messageData)
if message is None:
# nothing to see. move along.
return IGN
logger.debug(repr(message))
if self.getPolicy('SEND_TAG'):
if isinstance(message, basestring):
# received a plaintext message without tag
# we should not tag anymore
self.tagOffer = OFFER_REJECTED
else:
# got something OTR-ish, cool!
self.tagOffer = OFFER_ACCEPTED
if isinstance(message, proto.Query):
self.handleQuery(message, appdata=appdata)
if isinstance(message, proto.TaggedPlaintext):
# it's actually a plaintext message
if self.state != STATE_PLAINTEXT or \
self.getPolicy('REQUIRE_ENCRYPTION'):
# but we don't want plaintexts
raise UnencryptedMessage(message.msg)
raise NotOTRMessage(message.msg)
return IGN
if isinstance(message, proto.AKEMessage):
self.crypto.handleAKE(message, appdata=appdata)
return IGN
if isinstance(message, proto.DataMessage):
ignore = message.flags & proto.MSGFLAGS_IGNORE_UNREADABLE
if self.state != STATE_ENCRYPTED:
self.sendInternal(proto.Error(
'You sent encrypted data, but I wasn\'t expecting it.'
.encode('utf-8')), appdata=appdata)
if ignore:
return IGN
raise NotEncryptedError(EXC_UNREADABLE_MESSAGE)
try:
plaintext, tlvs = self.crypto.handleDataMessage(message)
self.processTLVs(tlvs, appdata=appdata)
if plaintext and self.lastSend < time() - HEARTBEAT_INTERVAL:
self.sendInternal(b'', appdata=appdata)
return plaintext or None, tlvs
except crypt.InvalidParameterError:
if ignore:
return IGN
logger.exception('decryption failed')
raise
if isinstance(message, basestring):
if self.state != STATE_PLAINTEXT or \
self.getPolicy('REQUIRE_ENCRYPTION'):
raise UnencryptedMessage(message)
if isinstance(message, proto.Error):
raise ErrorReceived(message)
raise NotOTRMessage(messageData)
def sendInternal(self, msg, tlvs=[], appdata=None):
self.sendMessage(FRAGMENT_SEND_ALL, msg, tlvs=tlvs, appdata=appdata,
flags=proto.MSGFLAGS_IGNORE_UNREADABLE)
def sendMessage(self, sendPolicy, msg, flags=0, tlvs=[], appdata=None):
if self.policyOtrEnabled():
self.lastSend = time()
if isinstance(msg, proto.OTRMessage):
# we want to send a protocol message (probably internal)
# so we don't need further protocol encryption
# also we can't add TLVs to arbitrary protocol messages
if tlvs:
raise TypeError('can\'t add tlvs to protocol message')
else:
# we got plaintext to send. encrypt it
msg = self.processOutgoingMessage(msg, flags, tlvs)
if isinstance(msg, proto.OTRMessage) \
and not isinstance(msg, proto.Query):
# if it's a query message, it must not get fragmented
return self.sendFragmented(bytes(msg), policy=sendPolicy, appdata=appdata)
else:
msg = bytes(msg)
return msg
def processOutgoingMessage(self, msg, flags, tlvs=[]):
isQuery = self.parseExplicitQuery(msg) is not None
if isQuery:
return self.user.getDefaultQueryMessage(self.getPolicy)
if self.state == STATE_PLAINTEXT:
if self.getPolicy('REQUIRE_ENCRYPTION'):
if not isQuery:
self.lastMessage = msg
self.lastSend = time()
self.mayRetransmit = 2
# TODO notify
msg = self.user.getDefaultQueryMessage(self.getPolicy)
return msg
if self.getPolicy('SEND_TAG') and \
self.tagOffer != OFFER_REJECTED and \
self.shouldTagMessage(msg):
self.tagOffer = OFFER_SENT
versions = set()
if self.getPolicy('ALLOW_V1'):
versions.add(1)
if self.getPolicy('ALLOW_V2'):
versions.add(2)
return proto.TaggedPlaintext(msg, versions)
return msg
if self.state == STATE_ENCRYPTED:
msg = self.crypto.createDataMessage(msg, flags, tlvs)
self.lastSend = time()
return msg
if self.state == STATE_FINISHED:
raise NotEncryptedError(EXC_FINISHED)
def disconnect(self, appdata=None):
if self.state != STATE_FINISHED:
self.sendInternal(b'', tlvs=[proto.DisconnectTLV()], appdata=appdata)
self.setState(STATE_PLAINTEXT)
self.crypto.finished()
else:
self.setState(STATE_PLAINTEXT)
def setState(self, newstate):
self.state = newstate
def _wentEncrypted(self):
self.setState(STATE_ENCRYPTED)
def sendFragmented(self, msg, policy=FRAGMENT_SEND_ALL, appdata=None):
mms = self.maxMessageSize(appdata)
msgLen = len(msg)
if mms != 0 and msgLen > mms:
fms = mms - 19
fragments = [ msg[i:i+fms] for i in range(0, msgLen, fms) ]
fc = len(fragments)
if fc > 65535:
raise OverflowError('too many fragments')
for fi in range(len(fragments)):
ctr = unicode(fi+1) + ',' + unicode(fc) + ','
fragments[fi] = b'?OTR,' + ctr.encode('ascii') \
+ fragments[fi] + b','
if policy == FRAGMENT_SEND_ALL:
for f in fragments:
self.inject(f, appdata=appdata)
return None
elif policy == FRAGMENT_SEND_ALL_BUT_FIRST:
for f in fragments[1:]:
self.inject(f, appdata=appdata)
return fragments[0]
elif policy == FRAGMENT_SEND_ALL_BUT_LAST:
for f in fragments[:-1]:
self.inject(f, appdata=appdata)
return fragments[-1]
else:
if policy == FRAGMENT_SEND_ALL:
self.inject(msg, appdata=appdata)
return None
else:
return msg
def processTLVs(self, tlvs, appdata=None):
for tlv in tlvs:
if isinstance(tlv, proto.DisconnectTLV):
logger.info('got disconnect tlv, forcing finished state')
self.setState(STATE_FINISHED)
self.crypto.finished()
# TODO cleanup
continue
if isinstance(tlv, proto.SMPTLV):
self.crypto.smpHandle(tlv, appdata=appdata)
continue
logger.info('got unhandled tlv: {0!r}'.format(tlv))
def smpAbort(self, appdata=None):
if self.state != STATE_ENCRYPTED:
raise NotEncryptedError
self.crypto.smpAbort(appdata=appdata)
def smpIsValid(self):
return self.crypto.smp and self.crypto.smp.prog != crypt.SMPPROG_CHEATED
def smpIsSuccess(self):
return self.crypto.smp.prog == crypt.SMPPROG_SUCCEEDED \
if self.crypto.smp else None
def smpGotSecret(self, secret, question=None, appdata=None):
if self.state != STATE_ENCRYPTED:
raise NotEncryptedError
self.crypto.smpSecret(secret, question=question, appdata=appdata)
def smpInit(self, secret, question=None, appdata=None):
if self.state != STATE_ENCRYPTED:
raise NotEncryptedError
self.crypto.smp = None
self.crypto.smpSecret(secret, question=question, appdata=appdata)
def handleQuery(self, message, appdata=None):
if 2 in message.versions and self.getPolicy('ALLOW_V2'):
self.authStartV2(appdata=appdata)
elif 1 in message.versions and self.getPolicy('ALLOW_V1'):
self.authStartV1(appdata=appdata)
def authStartV1(self, appdata=None):
raise NotImplementedError()
def authStartV2(self, appdata=None):
self.crypto.startAKE(appdata=appdata)
def parseExplicitQuery(self, message):
otrTagPos = message.find(proto.OTRTAG)
if otrTagPos == -1:
return None
indexBase = otrTagPos + len(proto.OTRTAG)
if len(message) <= indexBase:
return None
compare = message[indexBase]
hasq = compare == b'?'[0]
hasv = compare == b'v'[0]
if not hasq and not hasv:
return None
hasv |= len(message) > indexBase+1 and message[indexBase+1] == b'v'[0]
if hasv:
end = message.find(b'?', indexBase+1)
else:
end = indexBase+1
return message[indexBase:end]
def parse(self, message, nofragment=False):
otrTagPos = message.find(proto.OTRTAG)
if otrTagPos == -1:
if proto.MESSAGE_TAG_BASE in message:
return proto.TaggedPlaintext.parse(message)
else:
return message
indexBase = otrTagPos + len(proto.OTRTAG)
if len(message) <= indexBase:
return message
compare = message[indexBase]
if nofragment is False and compare == b','[0]:
message = self.fragmentAccumulate(message[indexBase:])
if message is None:
return None
else:
return self.parse(message, nofragment=True)
else:
self.discardFragment()
queryPayload = self.parseExplicitQuery(message)
if queryPayload is not None:
return proto.Query.parse(queryPayload)
if compare == b':'[0] and len(message) > indexBase + 4:
try:
infoTag = base64.b64decode(message[indexBase+1:indexBase+5])
classInfo = struct.unpack(b'!HB', infoTag)
cls = proto.messageClasses.get(classInfo, None)
if cls is None:
return message
logger.debug('{user} got msg {typ!r}' \
.format(user=self.user.name, typ=cls))
return cls.parsePayload(message[indexBase+5:])
except (TypeError, struct.error):
logger.exception('could not parse OTR message %s', message)
return message
if message[indexBase:indexBase+7] == b' Error:':
return proto.Error(message[indexBase+7:])
return message
def maxMessageSize(self, appdata=None):
"""Return the max message size for this context."""
return self.user.maxMessageSize
def getExtraKey(self, extraKeyAppId=None, extraKeyAppData=None, appdata=None):
""" retrieves the generated extra symmetric key.
if extraKeyAppId is set, notifies the chat partner about intended
usage (additional application specific information can be supplied in
extraKeyAppData).
returns the 256 bit symmetric key """
if self.state != STATE_ENCRYPTED:
raise NotEncryptedError
if extraKeyAppId is not None:
tlvs = [proto.ExtraKeyTLV(extraKeyAppId, extraKeyAppData)]
self.sendInternal(b'', tlvs=tlvs, appdata=appdata)
return self.crypto.extraKey
def shouldTagMessage(self, msg):
"""Hook to decide whether to tag a message based on its contents."""
return True
class Account(object):
contextclass = Context
def __init__(self, name, protocol, maxMessageSize, privkey=None):
self.name = name
self.privkey = privkey
self.policy = {}
self.protocol = protocol
self.ctxs = {}
self.trusts = {}
self.maxMessageSize = maxMessageSize
self.defaultQuery = '?OTRv{versions}?\nI would like to start ' \
'an Off-the-Record private conversation. However, you ' \
'do not have a plugin to support that.\nSee '\
'https://otr.cypherpunks.ca/ for more information.'
def __repr__(self):
return '<{cls}(name={name!r})>'.format(cls=self.__class__.__name__,
name=self.name)
def getPrivkey(self, autogen=True):
if self.privkey is None:
self.privkey = self.loadPrivkey()
if self.privkey is None:
if autogen is True:
self.privkey = compatcrypto.generateDefaultKey()
self.savePrivkey()
else:
raise LookupError
return self.privkey
def loadPrivkey(self):
raise NotImplementedError
def savePrivkey(self):
raise NotImplementedError
def saveTrusts(self):
raise NotImplementedError
def getContext(self, uid, newCtxCb=None):
if uid not in self.ctxs:
self.ctxs[uid] = self.contextclass(self, uid)
if callable(newCtxCb):
newCtxCb(self.ctxs[uid])
return self.ctxs[uid]
def getDefaultQueryMessage(self, policy):
v = '2' if policy('ALLOW_V2') else ''
msg = self.defaultQuery.format(versions=v)
return msg.encode('ascii')
def setTrust(self, key, fingerprint, trustLevel):
if key not in self.trusts:
self.trusts[key] = {}
self.trusts[key][fingerprint] = trustLevel
self.saveTrusts()
def getTrust(self, key, fingerprint, default=None):
if key not in self.trusts:
return default
return self.trusts[key].get(fingerprint, default)
def removeFingerprint(self, key, fingerprint):
if key in self.trusts and fingerprint in self.trusts[key]:
del self.trusts[key][fingerprint]
class NotEncryptedError(RuntimeError):
pass
class UnencryptedMessage(RuntimeError):
pass
class ErrorReceived(RuntimeError):
pass
class NotOTRMessage(RuntimeError):
pass