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python: Add PK bindings.

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This patch adds bindings to the PK part of the Olm library contained in
the pk.h header file.

Encryption, decryption as well as pickling/unpickling of the decryption
object is supported.

Signed-off-by: Damir Jelić <poljar@termina.org.uk>
This commit is contained in:
Damir Jelić 2018-11-28 14:54:09 +01:00 committed by Hubert Chathi
parent 0883a922ff
commit f160d693b6
5 changed files with 415 additions and 3 deletions
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12
python/Makefile
View file

@ -1,15 +1,21 @@
all: olm-python2 olm-python3
include/olm/olm.h: ../include/olm/olm.h ../include/olm/inbound_group_session.h ../include/olm/outbound_group_session.h
OLM_HEADERS = ../include/olm/olm.h ../include/olm/inbound_group_session.h \
../include/olm/outbound_group_session.h \
include/olm/olm.h: $(OLM_HEADERS)
mkdir -p include/olm
$(CPP) -I dummy -I ../include ../include/olm/olm.h -o include/olm/olm.h
# add memset to the header so that we can use it to clear buffers
echo 'void *memset(void *s, int c, size_t n);' >> include/olm/olm.h
olm-python2: include/olm/olm.h
include/olm/pk.h: include/olm/olm.h ../include/olm/pk.h
$(CPP) -I dummy -I ../include ../include/olm/pk.h -o include/olm/pk.h
olm-python2: include/olm/olm.h include/olm/pk.h
DEVELOP=$(DEVELOP) python2 setup.py build
olm-python3: include/olm/olm.h
olm-python3: include/olm/olm.h include/olm/pk.h
DEVELOP=$(DEVELOP) python3 setup.py build
install: install-python2 install-python3

7
python/olm/__init__.py
View file

@ -36,3 +36,10 @@ from .group_session import (
OutboundGroupSession,
OlmGroupSessionError
)
from .pk import (
PkMessage,
PkEncryption,
PkDecryption,
PkEncryptionError,
PkDecryptionError
)

346
python/olm/pk.py Normal file
View file

@ -0,0 +1,346 @@
# -*- coding: utf-8 -*-
# libolm python bindings
# Copyright © 2018 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 PK module.
This module contains bindings to the PK part of the Olm library.
It contains two classes PkDecryption and PkEncryption that are used to
establish an encrypted communication channel using public key encryption.
Examples:
>>> decryption = PkDecryption()
>>> encryption = PkEncryption(decryption.public_key)
>>> plaintext = "It's a secret to everybody."
>>> message = encryption.encrypt(plaintext)
>>> decrypted_plaintext = decryption.decrypt(message)
"""
from builtins import super
from typing import AnyStr, Type
from future.utils import bytes_to_native_str
from _libolm import ffi, lib # type: ignore
from ._finalize import track_for_finalization
from ._compat import URANDOM, to_bytearray
class PkEncryptionError(Exception):
"""libolm Pk encryption exception."""
class PkDecryptionError(Exception):
"""libolm Pk decryption exception."""
def _clear_pk_encryption(pk_struct):
lib.olm_clear_pk_encryption(pk_struct)
class PkMessage(object):
"""A PK encrypted message."""
def __init__(self, ephemeral_key, mac, ciphertext):
# type: (str, str, str) -> None
"""Create a new PK encrypted message.
Args:
ephemeral_key(str): the public part of the ephemeral key
used (together with the recipient's key) to generate a symmetric
encryption key.
mac(str): Message Authentication Code of the encrypted message
ciphertext(str): The cipher text of the encrypted message
"""
self.ephemeral_key = ephemeral_key
self.mac = mac
self.ciphertext = ciphertext
class PkEncryption(object):
"""PkEncryption class.
Represents the decryption part of a PK encrypted channel.
"""
def __init__(self, recipient_key):
# type: (AnyStr) -> None
"""Create a new PK encryption object.
Args:
recipient_key(str): a public key that will be used for encryption
"""
if not recipient_key:
raise ValueError("Recipient key can't be empty")
self._buf = ffi.new("char[]", lib.olm_pk_encryption_size())
self._pk_encryption = lib.olm_pk_encryption(self._buf)
track_for_finalization(self, self._pk_encryption, _clear_pk_encryption)
byte_key = to_bytearray(recipient_key)
lib.olm_pk_encryption_set_recipient_key(
self._pk_encryption,
ffi.from_buffer(byte_key),
len(byte_key)
)
# clear out copies of the key
if byte_key is not recipient_key: # pragma: no cover
for i in range(0, len(byte_key)):
byte_key[i] = 0
def _check_error(self, ret): # pragma: no cover
# type: (int) -> None
if ret != lib.olm_error():
return
last_error = bytes_to_native_str(
ffi.string(lib.olm_pk_encryption_last_error(self._pk_encryption)))
raise PkEncryptionError(last_error)
def encrypt(self, plaintext):
# type: (AnyStr) -> PkMessage
"""Encrypt a message.
Returns the encrypted PkMessage.
Args:
plaintext(str): A string that will be encrypted using the
PkEncryption object.
"""
byte_plaintext = to_bytearray(plaintext)
r_length = lib.olm_pk_encrypt_random_length(self._pk_encryption)
random = URANDOM(r_length)
random_buffer = ffi.new("char[]", random)
ciphertext_length = lib.olm_pk_ciphertext_length(
self._pk_encryption, len(byte_plaintext)
)
ciphertext = ffi.new("char[]", ciphertext_length)
mac_length = lib.olm_pk_mac_length(self._pk_encryption)
mac = ffi.new("char[]", mac_length)
ephemeral_key_size = lib.olm_pk_key_length()
ephemeral_key = ffi.new("char[]", ephemeral_key_size)
ret = lib.olm_pk_encrypt(
self._pk_encryption,
ffi.from_buffer(byte_plaintext), len(byte_plaintext),
ciphertext, ciphertext_length,
mac, mac_length,
ephemeral_key, ephemeral_key_size,
random_buffer, r_length
)
try:
self._check_error(ret)
finally: # pragma: no cover
# clear out copies of plaintext
if byte_plaintext is not plaintext:
for i in range(0, len(byte_plaintext)):
byte_plaintext[i] = 0
message = PkMessage(
bytes_to_native_str(
ffi.unpack(ephemeral_key, ephemeral_key_size)),
bytes_to_native_str(
ffi.unpack(mac, mac_length)),
bytes_to_native_str(
ffi.unpack(ciphertext, ciphertext_length))
)
return message
def _clear_pk_decryption(pk_struct):
lib.olm_clear_pk_decryption(pk_struct)
class PkDecryption(object):
"""PkDecryption class.
Represents the decryption part of a PK encrypted channel.
Attributes:
public_key (str): The public key of the PkDecryption object, can be
shared and used to create a PkEncryption object.
"""
def __new__(cls):
# type: (Type[PkDecryption]) -> PkDecryption
obj = super().__new__(cls)
obj._buf = ffi.new("char[]", lib.olm_pk_decryption_size())
obj._pk_decryption = lib.olm_pk_decryption(obj._buf)
obj.public_key = None
track_for_finalization(obj, obj._pk_decryption, _clear_pk_decryption)
return obj
def __init__(self):
if False: # pragma: no cover
self._pk_decryption = self._pk_decryption # type: ffi.cdata
random_length = lib.olm_pk_private_key_length()
random = URANDOM(random_length)
random_buffer = ffi.new("char[]", random)
key_length = lib.olm_pk_key_length()
key_buffer = ffi.new("char[]", key_length)
ret = lib.olm_pk_key_from_private(
self._pk_decryption,
key_buffer, key_length,
random_buffer, random_length
)
self._check_error(ret)
self.public_key = bytes_to_native_str(ffi.unpack(
key_buffer,
key_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_pk_decryption_last_error(self._pk_decryption)))
raise PkDecryptionError(last_error)
def pickle(self, passphrase=""):
# type: (str) -> bytes
"""Store a PkDecryption object.
Stores a PkDecryption object as a base64 string. Encrypts the object
using the supplied passphrase. Returns a byte object containing the
base64 encoded string of the pickled session.
Args:
passphrase(str, optional): The passphrase to be used to encrypt
the object.
"""
byte_key = to_bytearray(passphrase)
pickle_length = lib.olm_pickle_pk_decryption_length(
self._pk_decryption
)
pickle_buffer = ffi.new("char[]", pickle_length)
ret = lib.olm_pickle_pk_decryption(
self._pk_decryption,
ffi.from_buffer(byte_key), len(byte_key),
pickle_buffer, pickle_length
)
try:
self._check_error(ret)
finally:
# zero 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=""):
# types: (bytes, str) -> PkDecryption
"""Restore a previously stored PkDecryption object.
Creates a PkDecryption object from a pickled base64 string. Decrypts
the pickled object using the supplied passphrase.
Raises PkDecryptionError 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
PkDecryption object
passphrase(str, optional): The passphrase used to encrypt the
object
"""
if not pickle:
raise ValueError("Pickle can't be empty")
byte_key = to_bytearray(passphrase)
pickle_buffer = ffi.new("char[]", pickle)
pubkey_length = lib.olm_pk_key_length()
pubkey_buffer = ffi.new("char[]", pubkey_length)
obj = cls.__new__(cls)
ret = lib.olm_unpickle_pk_decryption(
obj._pk_decryption,
ffi.from_buffer(byte_key), len(byte_key),
pickle_buffer, len(pickle),
pubkey_buffer, pubkey_length)
try:
obj._check_error(ret)
finally:
for i in range(0, len(byte_key)):
byte_key[i] = 0
obj.public_key = bytes_to_native_str(ffi.unpack(
pubkey_buffer,
pubkey_length
))
return obj
def decrypt(self, message):
# type (PkMessage) -> str
"""Decrypt a previously encrypted Pk message.
Returns the decrypted plaintext.
Raises PkDecryptionError on failure.
Args:
message(PkMessage): the pk message to decrypt.
"""
ephemeral_key = to_bytearray(message.ephemeral_key)
ephemeral_key_size = len(ephemeral_key)
mac = to_bytearray(message.mac)
mac_length = len(mac)
ciphertext = to_bytearray(message.ciphertext)
ciphertext_length = len(ciphertext)
max_plaintext_length = lib.olm_pk_max_plaintext_length(
self._pk_decryption,
ciphertext_length
)
plaintext_buffer = ffi.new("char[]", max_plaintext_length)
ret = lib.olm_pk_decrypt(
self._pk_decryption,
ffi.from_buffer(ephemeral_key), ephemeral_key_size,
ffi.from_buffer(mac), mac_length,
ffi.from_buffer(ciphertext), ciphertext_length,
plaintext_buffer, max_plaintext_length)
self._check_error(ret)
plaintext = (ffi.unpack(
plaintext_buffer,
ret
))
# clear out copies of the plaintext
lib.memset(plaintext_buffer, 0, max_plaintext_length)
return bytes_to_native_str(plaintext)

4
python/olm_build.py
View file

@ -39,6 +39,7 @@ ffibuilder.set_source(
#include <olm/olm.h>
#include <olm/inbound_group_session.h>
#include <olm/outbound_group_session.h>
#include <olm/pk.h>
""",
libraries=["olm"],
extra_compile_args=compile_args,
@ -47,5 +48,8 @@ ffibuilder.set_source(
with open(os.path.join(PATH, "include/olm/olm.h")) as f:
ffibuilder.cdef(f.read(), override=True)
with open(os.path.join(PATH, "include/olm/pk.h")) as f:
ffibuilder.cdef(f.read(), override=True)
if __name__ == "__main__":
ffibuilder.compile(verbose=True)

49
python/tests/pk_test.py Normal file
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@ -0,0 +1,49 @@
import pytest
from olm import PkDecryption, PkDecryptionError, PkEncryption
class TestClass(object):
def test_invalid_encryption(self):
with pytest.raises(ValueError):
PkEncryption("")
def test_decrytion(self):
decryption = PkDecryption()
encryption = PkEncryption(decryption.public_key)
plaintext = "It's a secret to everybody."
message = encryption.encrypt(plaintext)
decrypted_plaintext = decryption.decrypt(message)
isinstance(decrypted_plaintext, str)
assert plaintext == decrypted_plaintext
def test_invalid_decrytion(self):
decryption = PkDecryption()
encryption = PkEncryption(decryption.public_key)
plaintext = "It's a secret to everybody."
message = encryption.encrypt(plaintext)
message.ephemeral_key = "?"
with pytest.raises(PkDecryptionError):
decryption.decrypt(message)
def test_pickling(self):
decryption = PkDecryption()
encryption = PkEncryption(decryption.public_key)
plaintext = "It's a secret to everybody."
message = encryption.encrypt(plaintext)
pickle = decryption.pickle()
unpickled = PkDecryption.from_pickle(pickle)
decrypted_plaintext = unpickled.decrypt(message)
assert plaintext == decrypted_plaintext
def test_invalid_unpickling(self):
with pytest.raises(ValueError):
PkDecryption.from_pickle("")
def test_invalid_pass_pickling(self):
decryption = PkDecryption()
pickle = decryption.pickle("Secret")
with pytest.raises(PkDecryptionError):
PkDecryption.from_pickle(pickle, "Not secret")