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Implement MtProto 2.0 (closes #484, thanks @delivrance!)
Huge shoutout to @delivrance's pyrogram, specially this commit: pyrogram/pyrogram/commit/42f9a2d6994baaf9ecad590d1ff4d175a8c56454
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@ -56,8 +56,11 @@ class BinaryReader:
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return int.from_bytes(
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self.read(bits // 8), byteorder='little', signed=signed)
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def read(self, length):
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def read(self, length=None):
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"""Read the given amount of bytes."""
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if length is None:
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return self.reader.read()
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result = self.reader.read(length)
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if len(result) != length:
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raise BufferError(
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@ -1,6 +1,11 @@
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"""Various helpers not related to the Telegram API itself"""
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from hashlib import sha1, sha256
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import os
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import struct
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from hashlib import sha1, sha256
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from telethon.crypto import AES
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from telethon.extensions import BinaryReader
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# region Multiple utilities
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@ -21,9 +26,48 @@ def ensure_parent_dir_exists(file_path):
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# region Cryptographic related utils
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def pack_message(session, message):
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"""Packs a message following MtProto 2.0 guidelines"""
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# See https://core.telegram.org/mtproto/description
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data = struct.pack('<qq', session.salt, session.id) + bytes(message)
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padding = os.urandom(-(len(data) + 12) % 16 + 12)
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# Being substr(what, offset, length); x = 0 for client
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# "msg_key_large = SHA256(substr(auth_key, 88+x, 32) + pt + padding)"
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msg_key_large = sha256(
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session.auth_key.key[88:88 + 32] + data + padding).digest()
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# "msg_key = substr (msg_key_large, 8, 16)"
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msg_key = msg_key_large[8:24]
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aes_key, aes_iv = calc_key_2(session.auth_key.key, msg_key, True)
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key_id = struct.pack('<Q', session.auth_key.key_id)
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return key_id + msg_key + AES.encrypt_ige(data + padding, aes_key, aes_iv)
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def unpack_message(session, reader):
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"""Unpacks a message following MtProto 2.0 guidelines"""
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# See https://core.telegram.org/mtproto/description
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reader.read_long(signed=False) # remote_auth_key_id
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msg_key = reader.read(16)
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aes_key, aes_iv = calc_key_2(session.auth_key.key, msg_key, False)
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data = BinaryReader(AES.decrypt_ige(reader.read(), aes_key, aes_iv))
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data.read_long() # remote_salt
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data.read_long() # remote_session_id
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remote_msg_id = data.read_long()
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remote_sequence = data.read_int()
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msg_len = data.read_int()
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message = data.read(msg_len)
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return message, remote_msg_id, remote_sequence
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def calc_key(shared_key, msg_key, client):
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"""Calculate the key based on Telegram guidelines,
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specifying whether it's the client or not
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"""
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Calculate the key based on Telegram guidelines,
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specifying whether it's the client or not.
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"""
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x = 0 if client else 8
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@ -40,6 +84,23 @@ def calc_key(shared_key, msg_key, client):
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return key, iv
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def calc_key_2(auth_key, msg_key, client):
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"""
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Calculate the key based on Telegram guidelines
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for MtProto 2, specifying whether it's the client or not.
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"""
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# https://core.telegram.org/mtproto/description#defining-aes-key-and-initialization-vector
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x = 0 if client else 8
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sha256a = sha256(msg_key + auth_key[x: x + 36]).digest()
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sha256b = sha256(auth_key[x + 40:x + 76] + msg_key).digest()
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aes_key = sha256a[:8] + sha256b[8:24] + sha256a[24:32]
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aes_iv = sha256b[:8] + sha256a[8:24] + sha256b[24:32]
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return aes_key, aes_iv
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def calc_msg_key(data):
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"""Calculates the message key from the given data"""
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return sha1(data).digest()[4:20]
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@ -156,17 +156,7 @@ class MtProtoSender:
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:param message: the TLMessage to be sent.
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"""
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plain_text = \
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struct.pack('<qq', self.session.salt, self.session.id) \
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+ bytes(message)
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msg_key = utils.calc_msg_key(plain_text)
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key_id = struct.pack('<Q', self.session.auth_key.key_id)
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key, iv = utils.calc_key(self.session.auth_key.key, msg_key, True)
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cipher_text = AES.encrypt_ige(plain_text, key, iv)
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result = key_id + msg_key + cipher_text
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self.connection.send(result)
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self.connection.send(utils.pack_message(self.session, message))
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def _decode_msg(self, body):
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"""
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@ -175,34 +165,14 @@ class MtProtoSender:
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:param body: the body to be decoded.
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:return: a tuple of (decoded message, remote message id, remote seq).
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"""
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message = None
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remote_msg_id = None
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remote_sequence = None
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if len(body) < 8:
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if body == b'l\xfe\xff\xff':
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raise BrokenAuthKeyError()
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else:
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raise BufferError("Can't decode packet ({})".format(body))
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with BinaryReader(body) as reader:
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if len(body) < 8:
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if body == b'l\xfe\xff\xff':
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raise BrokenAuthKeyError()
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else:
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raise BufferError("Can't decode packet ({})".format(body))
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# TODO Check for both auth key ID and msg_key correctness
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reader.read_long() # remote_auth_key_id
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msg_key = reader.read(16)
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key, iv = utils.calc_key(self.session.auth_key.key, msg_key, False)
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plain_text = AES.decrypt_ige(
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reader.read(len(body) - reader.tell_position()), key, iv)
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with BinaryReader(plain_text) as plain_text_reader:
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plain_text_reader.read_long() # remote_salt
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plain_text_reader.read_long() # remote_session_id
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remote_msg_id = plain_text_reader.read_long()
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remote_sequence = plain_text_reader.read_int()
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msg_len = plain_text_reader.read_int()
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message = plain_text_reader.read(msg_len)
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return message, remote_msg_id, remote_sequence
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return utils.unpack_message(self.session, reader)
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def _process_msg(self, msg_id, sequence, reader, state):
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"""
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