path: root/python/olm/pk.py

# -*- 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,
as well as a class PkSigning that is used to sign a message.

Examples:
    >>> decryption = PkDecryption()
    >>> encryption = PkEncryption(decryption.public_key)
    >>> plaintext = "It's a secret to everybody."
    >>> message = encryption.encrypt(plaintext)
    >>> decrypted_plaintext = decryption.decrypt(message)
    >>> seed = PkSigning.generate_seed()
    >>> signing = PkSigning(seed)
    >>> signature = signing.sign(plaintext)
    >>> ed25519_verify(signing.public_key, plaintext, signature)

"""

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 ._compat import URANDOM, to_bytearray, to_unicode_str
from ._finalize import track_for_finalization


class PkEncryptionError(Exception):
    """libolm Pk encryption exception."""


class PkDecryptionError(Exception):
    """libolm Pk decryption exception."""


class PkSigningError(Exception):
    """libolm Pk signing 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, unicode_errors="replace"):
        # type (PkMessage, str) -> str
        """Decrypt a previously encrypted Pk message.

        Returns the decrypted plaintext.
        Raises PkDecryptionError on failure.

        Args:
            message(PkMessage): the pk message to decrypt.
            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.
        """
        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 to_unicode_str(plaintext, errors=unicode_errors)


def _clear_pk_signing(pk_struct):
    lib.olm_clear_pk_signing(pk_struct)


class PkSigning(object):
    """PkSigning class.

    Signs messages using public key cryptography.

    Attributes:
        public_key (str): The public key of the PkSigning object, can be
            shared and used to verify using Utility.ed25519_verify.

    """

    def __init__(self, seed):
        # type: (bytes) -> None
        """Create a new signing object.

        Args:
            seed(bytes): the seed to use as the private key for signing.  The
                seed must have the same length as the seeds generated by
                PkSigning.generate_seed().
        """
        if not seed:
            raise ValueError("seed can't be empty")

        self._buf = ffi.new("char[]", lib.olm_pk_signing_size())
        self._pk_signing = lib.olm_pk_signing(self._buf)
        track_for_finalization(self, self._pk_signing, _clear_pk_signing)

        seed_buffer = ffi.new("char[]", seed)

        pubkey_length = lib.olm_pk_signing_public_key_length()
        pubkey_buffer = ffi.new("char[]", pubkey_length)

        ret = lib.olm_pk_signing_key_from_seed(
            self._pk_signing,
            pubkey_buffer, pubkey_length,
            seed_buffer, len(seed)
        )

        # zero out copies of the seed
        lib.memset(seed_buffer, 0, len(seed))

        self._check_error(ret)

        self.public_key = bytes_to_native_str(
            ffi.unpack(pubkey_buffer, pubkey_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_signing_last_error(self._pk_signing)))

        raise PkSigningError(last_error)

    @classmethod
    def generate_seed(cls):
        # type: () -> bytes
        """Generate a random seed.
        """
        random_length = lib.olm_pk_signing_seed_length()
        random = URANDOM(random_length)

        return random

    def sign(self, message):
        # type: (AnyStr) -> str
        """Sign a message

        Returns the signature.
        Raises PkSigningError on failure.

        Args:
            message(str): the message to sign.
        """
        bytes_message = to_bytearray(message)

        signature_length = lib.olm_pk_signature_length()
        signature_buffer = ffi.new("char[]", signature_length)

        ret = lib.olm_pk_sign(
            self._pk_signing,
            ffi.from_buffer(bytes_message), len(bytes_message),
            signature_buffer, signature_length)
        self._check_error(ret)

        return bytes_to_native_str(
            ffi.unpack(signature_buffer, signature_length)
        )