Telethon/telethon/network/connection/tcpobfuscated.py

import os
from datetime import timedelta

from .tcpfull import ConnectionTcpFull
from .tcpabridged import ConnectionTcpAbridged
from ...crypto import AESModeCTR


class ConnectionTcpObfuscated(ConnectionTcpAbridged):
    """
    Encodes the packet just like `ConnectionTcpAbridged`, but encrypts
    every message with a randomly generated key using the
    AES-CTR mode so the packets are harder to discern.
    """
    def __init__(self, *, loop, proxy=None, timeout=timedelta(seconds=5)):
        super().__init__(loop=loop, proxy=proxy, timeout=timeout)
        self._aes_encrypt, self._aes_decrypt = None, None
        self.read = lambda s: self._aes_decrypt.encrypt(self.conn.read(s))
        self.write = lambda d: self.conn.write(self._aes_encrypt.encrypt(d))

    async def connect(self, ip, port):
        result = await ConnectionTcpFull.connect(self, ip, port)
        # Obfuscated messages secrets cannot start with any of these
        keywords = (b'PVrG', b'GET ', b'POST', b'\xee' * 4)
        while True:
            random = os.urandom(64)
            if (random[0] != b'\xef' and
                    random[:4] not in keywords and
                    random[4:4] != b'\0\0\0\0'):
                break

        random = list(random)
        random[56] = random[57] = random[58] = random[59] = 0xef
        random_reversed = random[55:7:-1]  # Reversed (8, len=48)

        # encryption has "continuous buffer" enabled
        encrypt_key = bytes(random[8:40])
        encrypt_iv = bytes(random[40:56])
        decrypt_key = bytes(random_reversed[:32])
        decrypt_iv = bytes(random_reversed[32:48])

        self._aes_encrypt = AESModeCTR(encrypt_key, encrypt_iv)
        self._aes_decrypt = AESModeCTR(decrypt_key, decrypt_iv)

        random[56:64] = self._aes_encrypt.encrypt(bytes(random))[56:64]
        await self.conn.write(bytes(random))
        return result