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# Pyrogram - Telegram MTProto API Client Library for Python

# 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

try:

message = Message.read(data)

except KeyError as e:

left = data.read().hex()

left = [left[i:i + 64] for i in range(0, len(left), 64)]

left = [[left[i:i + 8] for i in range(0, len(left), 8)] for left in left]

left = "\n".join(" ".join(x for x in left) for left in left)

raise ValueError(f"Unknown constructor found: {hex(e.args[0])}\n{left}")

# 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

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