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+# -*- coding: utf-8 -*-
+# libolm python bindings
+# Copyright © 2015-2017 OpenMarket Ltd
+# Copyright © 2019 Damir Jelić <poljar@termina.org.uk>
+#
+# 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 SAS module.
+
+This module contains functions to perform key verification using the Short
+Authentication String (SAS) method.
+
+Examples:
+ >>> sas = Sas()
+ >>> bob_key = "3p7bfXt9wbTTW2HC7OQ1Nz+DQ8hbeGdNrfx+FG+IK08"
+ >>> message = "Hello world!"
+ >>> extra_info = "MAC"
+ >>> sas_alice.set_their_pubkey(bob_key)
+ >>> sas_alice.calculate_mac(message, extra_info)
+ >>> sas_alice.generate_bytes(extra_info, 5)
+
+"""
+
+from functools import wraps
+from builtins import bytes
+from typing import Optional
+
+from future.utils import bytes_to_native_str
+
+from _libolm import ffi, lib
+
+from ._compat import URANDOM, to_bytes, to_bytearray
+from ._finalize import track_for_finalization
+
+
+def other_pubkey_set(func):
+ """Ensure that the other pubkey is added to the Sas object."""
+ @wraps(func)
+ def wrapper(self, *args, **kwargs):
+ if not self.other_key_set:
+ raise OlmSasError("The other public key isn't set.")
+ return func(self, *args, **kwargs)
+ return wrapper
+
+
+def _clear_sas(sas):
+ # type: (ffi.cdata) -> None
+ lib.olm_clear_sas(sas)
+
+
+class OlmSasError(Exception):
+ """libolm Sas error exception."""
+
+
+class Sas(object):
+ """libolm Short Authenticaton String (SAS) class."""
+
+ def __init__(self, other_users_pubkey=None):
+ # type: (Optional[str]) -> None
+ """Create a new SAS object.
+
+ Args:
+ other_users_pubkey(str, optional): The other users public key, this
+ key is necesary to generate bytes for the authentication string
+ as well as to calculate the MAC.
+
+ Attributes:
+ other_key_set (bool): A boolean flag that tracks if we set the
+ other users public key for this SAS object.
+
+ Raises OlmSasError on failure.
+
+ """
+ self._buf = ffi.new("char[]", lib.olm_sas_size())
+ self._sas = lib.olm_sas(self._buf)
+ self.other_key_set = False
+ track_for_finalization(self, self._sas, _clear_sas)
+
+ random_length = lib.olm_create_sas_random_length(self._sas)
+ random = URANDOM(random_length)
+
+ self._create_sas(random, random_length)
+
+ if other_users_pubkey:
+ self.set_their_pubkey(other_users_pubkey)
+
+ def _create_sas(self, buffer, buffer_length):
+ self._check_error(
+ lib.olm_create_sas(
+ self._sas,
+ ffi.from_buffer(buffer),
+ buffer_length
+ )
+ )
+
+ def _check_error(self, ret):
+ # type: (int) -> None
+ if ret != lib.olm_error():
+ return
+
+ last_error = bytes_to_native_str(
+ ffi.string((lib.olm_sas_last_error(self._sas))))
+
+ raise OlmSasError(last_error)
+
+ @property
+ def pubkey(self):
+ # type: () -> str
+ """Get the public key for the SAS object.
+
+ This returns the public key of the SAS object that can then be shared
+ with another user to perform the authentication process.
+
+ Raises OlmSasError on failure.
+
+ """
+ pubkey_length = lib.olm_sas_pubkey_length(self._sas)
+ pubkey_buffer = ffi.new("char[]", pubkey_length)
+
+ self._check_error(
+ lib.olm_sas_get_pubkey(self._sas, pubkey_buffer, pubkey_length)
+ )
+
+ return bytes_to_native_str(ffi.unpack(pubkey_buffer, pubkey_length))
+
+ def set_their_pubkey(self, key):
+ # type: (str) -> None
+ """Set the public key of the other user.
+
+ This sets the public key of the other user, it needs to be set before
+ bytes can be generated for the authentication string and a MAC can be
+ calculated.
+
+ Args:
+ key (str): The other users public key.
+
+ Raises OlmSasError on failure.
+
+ """
+ byte_key = to_bytearray(key)
+
+ self._check_error(
+ lib.olm_sas_set_their_key(
+ self._sas,
+ ffi.from_buffer(byte_key),
+ len(byte_key)
+ )
+ )
+ self.other_key_set = True
+
+ @other_pubkey_set
+ def generate_bytes(self, extra_info, length):
+ # type: (str, int) -> bytes
+ """Generate bytes to use for the short authentication string.
+
+ Args:
+ extra_info (str): Extra information to mix in when generating the
+ bytes.
+ length (int): The number of bytes to generate.
+
+ Raises OlmSasError if the other users persons public key isn't set or
+ an internal Olm error happens.
+
+ """
+ if length < 1:
+ raise ValueError("The length needs to be a positive integer value")
+
+ byte_info = to_bytearray(extra_info)
+ out_buffer = ffi.new("char[]", length)
+
+ self._check_error(
+ lib.olm_sas_generate_bytes(
+ self._sas,
+ ffi.from_buffer(byte_info),
+ len(byte_info),
+ out_buffer,
+ length
+ )
+ )
+
+ return ffi.unpack(out_buffer, length)
+
+ @other_pubkey_set
+ def calculate_mac(self, message, extra_info):
+ # type: (str, str) -> str
+ """Generate a message authentication code based on the shared secret.
+
+ Args:
+ message (str): The message to produce the authentication code for.
+ extra_info (str): Extra information to mix in when generating the
+ MAC
+
+ Raises OlmSasError on failure.
+
+ """
+ byte_message = to_bytes(message)
+ byte_info = to_bytes(extra_info)
+
+ mac_length = lib.olm_sas_mac_length(self._sas)
+ mac_buffer = ffi.new("char[]", mac_length)
+
+ self._check_error(
+ lib.olm_sas_calculate_mac(
+ self._sas,
+ ffi.from_buffer(byte_message),
+ len(byte_message),
+ ffi.from_buffer(byte_info),
+ len(byte_info),
+ mac_buffer,
+ mac_length
+ )
+ )
+ return bytes_to_native_str(ffi.unpack(mac_buffer, mac_length))