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# Pyrogram - Telegram MTProto API Client Library for Python
# Copyright (C) 2017-2018 Dan Tès <https://github.com/delivrance>
#
# This file is part of Pyrogram.
#
# Pyrogram 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
# (at your option) any later version.
#
# Pyrogram 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 Pyrogram. If not, see <http://www.gnu.org/licenses/>.
from hashlib import sha256
from io import BytesIO
from os import urandom
from pyrogram.raw.core import Message, Long
from . import aes
def kdf(auth_key: bytes, msg_key: bytes, outgoing: bool) -> tuple:
# https://core.telegram.org/mtproto/description#defining-aes-key-and-initialization-vector
x = 0 if outgoing else 8
sha256_a = sha256(msg_key + auth_key[x: x + 36]).digest()
sha256_b = sha256(auth_key[x + 40:x + 76] + msg_key).digest() # 76 = 40 + 36
aes_key = sha256_a[:8] + sha256_b[8:24] + sha256_a[24:32]
aes_iv = sha256_b[:8] + sha256_a[8:24] + sha256_b[24:32]
return aes_key, aes_iv
def pack(message: Message, salt: int, session_id: bytes, auth_key: bytes, auth_key_id: bytes) -> bytes:
data = Long(salt) + session_id + message.write()
padding = urandom(-(len(data) + 12) % 16 + 12)
# 88 = 88 + 0 (outgoing message)
msg_key_large = sha256(auth_key[88: 88 + 32] + data + padding).digest()
msg_key = msg_key_large[8:24]
aes_key, aes_iv = kdf(auth_key, msg_key, True)
return auth_key_id + msg_key + aes.ige256_encrypt(data + padding, aes_key, aes_iv)
def unpack(b: BytesIO, session_id: bytes, auth_key: bytes, auth_key_id: bytes) -> Message:
assert b.read(8) == auth_key_id, b.getvalue()
msg_key = b.read(16)
aes_key, aes_iv = kdf(auth_key, msg_key, False)
data = BytesIO(aes.ige256_decrypt(b.read(), aes_key, aes_iv))
data.read(8)
# https://core.telegram.org/mtproto/security_guidelines#checking-session-id
assert data.read(8) == session_id
message = Message.read(data)
# https://core.telegram.org/mtproto/security_guidelines#checking-sha256-hash-value-of-msg-key
# https://core.telegram.org/mtproto/security_guidelines#checking-message-length
# 96 = 88 + 8 (incoming message)
assert msg_key == sha256(auth_key[96:96 + 32] + data.getvalue()).digest()[8:24]
# https://core.telegram.org/mtproto/security_guidelines#checking-msg-id
assert message.msg_id % 2 != 0
return message