# -*- coding: utf-8 -*- # libolm python bindings # Copyright © 2015-2017 OpenMarket Ltd # Copyright © 2018 Damir Jelić # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. """libolm Session module. This module contains the Olm Session part of the Olm library. It is used to establish a peer-to-peer encrypted communication channel between two Olm accounts. Examples: >>> alice = Account() >>> bob = Account() >>> bob.generate_one_time_keys(1) >>> id_key = bob.identity_keys['curve25519'] >>> one_time = list(bob.one_time_keys["curve25519"].values())[0] >>> session = OutboundSession(alice, id_key, one_time) """ # pylint: disable=redefined-builtin,unused-import from builtins import bytes, super from typing import AnyStr, Optional, Type # pylint: disable=no-name-in-module from _libolm import ffi, lib # type: ignore from ._compat import URANDOM, to_bytearray, to_bytes, to_unicode_str from ._finalize import track_for_finalization # This is imported only for type checking purposes if False: from .account import Account # pragma: no cover class OlmSessionError(Exception): """libolm Session exception.""" class _OlmMessage(object): def __init__(self, ciphertext, message_type): # type: (AnyStr, ffi.cdata) -> None if not ciphertext: raise ValueError("Ciphertext can't be empty") # I don't know why mypy wants a type annotation here nor why AnyStr # doesn't work self.ciphertext = ciphertext # type: ignore self.message_type = message_type def __str__(self): # type: () -> str type_to_prefix = { lib.OLM_MESSAGE_TYPE_PRE_KEY: "PRE_KEY", lib.OLM_MESSAGE_TYPE_MESSAGE: "MESSAGE" } prefix = type_to_prefix[self.message_type] return "{} {}".format(prefix, self.ciphertext) class OlmPreKeyMessage(_OlmMessage): """Olm prekey message class Prekey messages are used to establish an Olm session. After the first message exchange the session switches to normal messages """ def __init__(self, ciphertext): # type: (AnyStr) -> None """Create a new Olm prekey message with the supplied ciphertext Args: ciphertext(str): The ciphertext of the prekey message. """ _OlmMessage.__init__(self, ciphertext, lib.OLM_MESSAGE_TYPE_PRE_KEY) def __repr__(self): # type: () -> str return "OlmPreKeyMessage({})".format(self.ciphertext) class OlmMessage(_OlmMessage): """Olm message class""" def __init__(self, ciphertext): # type: (AnyStr) -> None """Create a new Olm message with the supplied ciphertext Args: ciphertext(str): The ciphertext of the message. """ _OlmMessage.__init__(self, ciphertext, lib.OLM_MESSAGE_TYPE_MESSAGE) def __repr__(self): # type: () -> str return "OlmMessage({})".format(self.ciphertext) def _clear_session(session): # type: (ffi.cdata) -> None lib.olm_clear_session(session) class Session(object): """libolm Session class. This is an abstract class that can't be instantiated except when unpickling a previously pickled InboundSession or OutboundSession object with from_pickle. """ def __new__(cls): # type: (Type[Session]) -> Session obj = super().__new__(cls) obj._buf = ffi.new("char[]", lib.olm_session_size()) obj._session = lib.olm_session(obj._buf) track_for_finalization(obj, obj._session, _clear_session) return obj def __init__(self): # type: () -> None if type(self) is Session: raise TypeError("Session class may not be instantiated.") if False: self._session = self._session # type: ffi.cdata def _check_error(self, ret): # type: (int) -> None if ret != lib.olm_error(): return last_error = ffi.string(lib.olm_session_last_error(self._session)).decode() raise OlmSessionError(last_error) def pickle(self, passphrase=""): # type: (Optional[str]) -> bytes """Store an Olm session. Stores a session as a base64 string. Encrypts the session using the supplied passphrase. Returns a byte object containing the base64 encoded string of the pickled session. Raises OlmSessionError on failure. Args: passphrase(str, optional): The passphrase to be used to encrypt the session. """ byte_key = bytearray(passphrase, "utf-8") if passphrase else b"" pickle_length = lib.olm_pickle_session_length(self._session) pickle_buffer = ffi.new("char[]", pickle_length) try: self._check_error( lib.olm_pickle_session(self._session, ffi.from_buffer(byte_key), len(byte_key), pickle_buffer, pickle_length)) finally: # clear out copies of the passphrase for i in range(0, len(byte_key)): byte_key[i] = 0 return ffi.unpack(pickle_buffer, pickle_length) @classmethod def from_pickle(cls, pickle, passphrase=""): # type: (bytes, Optional[str]) -> Session """Load a previously stored Olm session. Loads a session from a pickled base64 string and returns a Session object. Decrypts the session using the supplied passphrase. Raises OlmSessionError on failure. If the passphrase doesn't match the one used to encrypt the session then the error message for the exception will be "BAD_ACCOUNT_KEY". If the base64 couldn't be decoded then the error message will be "INVALID_BASE64". Args: pickle(bytes): Base64 encoded byte string containing the pickled session passphrase(str, optional): The passphrase used to encrypt the session. """ if not pickle: raise ValueError("Pickle can't be empty") byte_key = bytearray(passphrase, "utf-8") if passphrase else b"" # copy because unpickle will destroy the buffer pickle_buffer = ffi.new("char[]", pickle) session = cls.__new__(cls) try: ret = lib.olm_unpickle_session(session._session, ffi.from_buffer(byte_key), len(byte_key), pickle_buffer, len(pickle)) session._check_error(ret) finally: # clear out copies of the passphrase for i in range(0, len(byte_key)): byte_key[i] = 0 return session def encrypt(self, plaintext): # type: (AnyStr) -> _OlmMessage """Encrypts a message using the session. Returns the ciphertext as a base64 encoded string on success. Raises OlmSessionError on failure. Args: plaintext(str): The plaintext message that will be encrypted. """ byte_plaintext = to_bytearray(plaintext) r_length = lib.olm_encrypt_random_length(self._session) random = URANDOM(r_length) try: message_type = lib.olm_encrypt_message_type(self._session) self._check_error(message_type) ciphertext_length = lib.olm_encrypt_message_length( self._session, len(byte_plaintext) ) ciphertext_buffer = ffi.new("char[]", ciphertext_length) self._check_error(lib.olm_encrypt( self._session, ffi.from_buffer(byte_plaintext), len(byte_plaintext), ffi.from_buffer(random), r_length, ciphertext_buffer, ciphertext_length, )) finally: # clear out copies of plaintext if byte_plaintext is not plaintext: for i in range(0, len(byte_plaintext)): byte_plaintext[i] = 0 if message_type == lib.OLM_MESSAGE_TYPE_PRE_KEY: return OlmPreKeyMessage( ffi.unpack( ciphertext_buffer, ciphertext_length ).decode()) elif message_type == lib.OLM_MESSAGE_TYPE_MESSAGE: return OlmMessage( ffi.unpack( ciphertext_buffer, ciphertext_length ).decode()) else: # pragma: no cover raise ValueError("Unknown message type") def decrypt(self, message, unicode_errors="replace"): # type: (_OlmMessage, str) -> str """Decrypts a message using the session. Returns the plaintext string on success. Raises OlmSessionError on failure. If the base64 couldn't be decoded then the error message will be "INVALID_BASE64". If the message is for an unsupported version of the protocol the error message will be "BAD_MESSAGE_VERSION". If the message couldn't be decoded then the error message will be "BAD_MESSAGE_FORMAT". If the MAC on the message was invalid then the error message will be "BAD_MESSAGE_MAC". Args: message(OlmMessage): The Olm message that will be decrypted. It can be either an OlmPreKeyMessage or an OlmMessage. unicode_errors(str, optional): The error handling scheme to use for unicode decoding errors. The default is "replace" meaning that the character that was unable to decode will be replaced with the unicode replacement character (U+FFFD). Other possible values are "strict", "ignore" and "xmlcharrefreplace" as well as any other name registered with codecs.register_error that can handle UnicodeEncodeErrors. """ if not message.ciphertext: raise ValueError("Ciphertext can't be empty") byte_ciphertext = to_bytes(message.ciphertext) # make a copy the ciphertext buffer, because # olm_decrypt_max_plaintext_length wants to destroy something ciphertext_buffer = ffi.new("char[]", byte_ciphertext) max_plaintext_length = lib.olm_decrypt_max_plaintext_length( self._session, message.message_type, ciphertext_buffer, len(byte_ciphertext) ) self._check_error(max_plaintext_length) plaintext_buffer = ffi.new("char[]", max_plaintext_length) # make a copy the ciphertext buffer, because # olm_decrypt_max_plaintext_length wants to destroy something ciphertext_buffer = ffi.new("char[]", byte_ciphertext) plaintext_length = lib.olm_decrypt( self._session, message.message_type, ciphertext_buffer, len(byte_ciphertext), plaintext_buffer, max_plaintext_length ) self._check_error(plaintext_length) plaintext = to_unicode_str( ffi.unpack(plaintext_buffer, plaintext_length), errors=unicode_errors ) # clear out copies of the plaintext lib.memset(plaintext_buffer, 0, max_plaintext_length) return plaintext @property def id(self): # type: () -> str """str: An identifier for this session. Will be the same for both ends of the conversation. """ id_length = lib.olm_session_id_length(self._session) id_buffer = ffi.new("char[]", id_length) self._check_error( lib.olm_session_id(self._session, id_buffer, id_length) ) return ffi.unpack(id_buffer, id_length).decode() def matches(self, message, identity_key=None): # type: (OlmPreKeyMessage, Optional[AnyStr]) -> bool """Checks if the PRE_KEY message is for this in-bound session. This can happen if multiple messages are sent to this session before this session sends a message in reply. Returns True if the session matches. Returns False if the session does not match. Raises OlmSessionError on failure. If the base64 couldn't be decoded then the error message will be "INVALID_BASE64". If the message was for an unsupported protocol version then the error message will be "BAD_MESSAGE_VERSION". If the message couldn't be decoded then then the error message will be * "BAD_MESSAGE_FORMAT". Args: message(OlmPreKeyMessage): The Olm prekey message that will checked if it is intended for this session. identity_key(str, optional): The identity key of the sender. To check if the message was also sent using this identity key. """ if not isinstance(message, OlmPreKeyMessage): raise TypeError("Matches can only be called with prekey messages.") if not message.ciphertext: raise ValueError("Ciphertext can't be empty") ret = None byte_ciphertext = to_bytes(message.ciphertext) # make a copy, because olm_matches_inbound_session(_from) will distroy # it message_buffer = ffi.new("char[]", byte_ciphertext) if identity_key: byte_id_key = to_bytes(identity_key) ret = lib.olm_matches_inbound_session_from( self._session, ffi.from_buffer(byte_id_key), len(byte_id_key), message_buffer, len(byte_ciphertext) ) else: ret = lib.olm_matches_inbound_session( self._session, message_buffer, len(byte_ciphertext)) self._check_error(ret) return bool(ret) def describe(self, buffer_length=600): # type: (int) -> str """ Generate a string describing the internal state of an olm session for debugging and logging purposes. Args: buffer_length(int): The size of buffer for the string. If the buffer is not large enough to hold the entire string, it will be truncated and will end with "...". A buffer length of 600 will be enough to hold any output. """ describe_buffer = ffi.new("char[]", buffer_length) lib.olm_session_describe( self._session, describe_buffer, buffer_length ) return ffi.string(describe_buffer).decode() class InboundSession(Session): """Inbound Olm session for p2p encrypted communication. """ def __new__(cls, account, message, identity_key=None): # type: (Account, OlmPreKeyMessage, Optional[AnyStr]) -> Session return super().__new__(cls) def __init__(self, account, message, identity_key=None): # type: (Account, OlmPreKeyMessage, Optional[AnyStr]) -> None """Create a new inbound Olm session. Create a new in-bound session for sending/receiving messages from an incoming prekey message. Raises OlmSessionError on failure. If the base64 couldn't be decoded then error message will be "INVALID_BASE64". If the message was for an unsupported protocol version then the errror message will be "BAD_MESSAGE_VERSION". If the message couldn't be decoded then then the error message will be "BAD_MESSAGE_FORMAT". If the message refers to an unknown one-time key then the error message will be "BAD_MESSAGE_KEY_ID". Args: account(Account): The Olm Account that will be used to create this session. message(OlmPreKeyMessage): The Olm prekey message that will checked that will be used to create this session. identity_key(str, optional): The identity key of the sender. To check if the message was also sent using this identity key. """ if not message.ciphertext: raise ValueError("Ciphertext can't be empty") super().__init__() byte_ciphertext = to_bytes(message.ciphertext) message_buffer = ffi.new("char[]", byte_ciphertext) if identity_key: byte_id_key = to_bytes(identity_key) identity_key_buffer = ffi.new("char[]", byte_id_key) self._check_error(lib.olm_create_inbound_session_from( self._session, account._account, identity_key_buffer, len(byte_id_key), message_buffer, len(byte_ciphertext) )) else: self._check_error(lib.olm_create_inbound_session( self._session, account._account, message_buffer, len(byte_ciphertext) )) class OutboundSession(Session): """Outbound Olm session for p2p encrypted communication.""" def __new__(cls, account, identity_key, one_time_key): # type: (Account, AnyStr, AnyStr) -> Session return super().__new__(cls) def __init__(self, account, identity_key, one_time_key): # type: (Account, AnyStr, AnyStr) -> None """Create a new outbound Olm session. Creates a new outbound session for sending messages to a given identity key and one-time key. Raises OlmSessionError on failure. If the keys couldn't be decoded as base64 then the error message will be "INVALID_BASE64". Args: account(Account): The Olm Account that will be used to create this session. identity_key(str): The identity key of the person with whom we want to start the session. one_time_key(str): A one-time key from the person with whom we want to start the session. """ if not identity_key: raise ValueError("Identity key can't be empty") if not one_time_key: raise ValueError("One-time key can't be empty") super().__init__() byte_id_key = to_bytes(identity_key) byte_one_time = to_bytes(one_time_key) session_random_length = lib.olm_create_outbound_session_random_length( self._session) random = URANDOM(session_random_length) self._check_error(lib.olm_create_outbound_session( self._session, account._account, ffi.from_buffer(byte_id_key), len(byte_id_key), ffi.from_buffer(byte_one_time), len(byte_one_time), ffi.from_buffer(random), session_random_length ))