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Create a self-contained MTProtoState

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This frees us from using entire Session objects in something
that's supposed to just send and receive items from the net.
This commit is contained in:
Lonami Exo
2018-06-09 11:34:01 +02:00
parent cc5753137c
commit adfe861e9f
5 changed files with 226 additions and 146 deletions
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76
telethon/helpers.py
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@@ -1,12 +1,7 @@
"""Various helpers not related to the Telegram API itself"""
import os
import struct
from hashlib import sha1, sha256
from .crypto import AES
from .errors import SecurityError, BrokenAuthKeyError
from .extensions import BinaryReader
# region Multiple utilities
@@ -27,77 +22,6 @@ def ensure_parent_dir_exists(file_path):
# region Cryptographic related utils
def pack_message(session, message):
"""Packs a message following MtProto 2.0 guidelines"""
# See https://core.telegram.org/mtproto/description
data = struct.pack('<qq', session.salt, session.id) + bytes(message)
padding = os.urandom(-(len(data) + 12) % 16 + 12)
# Being substr(what, offset, length); x = 0 for client
# "msg_key_large = SHA256(substr(auth_key, 88+x, 32) + pt + padding)"
msg_key_large = sha256(
session.auth_key.key[88:88 + 32] + data + padding).digest()
# "msg_key = substr (msg_key_large, 8, 16)"
msg_key = msg_key_large[8:24]
aes_key, aes_iv = calc_key(session.auth_key.key, msg_key, True)
key_id = struct.pack('<Q', session.auth_key.key_id)
return key_id + msg_key + AES.encrypt_ige(data + padding, aes_key, aes_iv)
def unpack_message(session, body):
"""Unpacks a message following MtProto 2.0 guidelines"""
# See https://core.telegram.org/mtproto/description
if len(body) < 8:
if body == b'l\xfe\xff\xff':
raise BrokenAuthKeyError()
else:
raise BufferError("Can't decode packet ({})".format(body))
key_id = struct.unpack('<Q', body[:8])[0]
if key_id != session.auth_key.key_id:
raise SecurityError('Server replied with an invalid auth key')
msg_key = body[8:24]
aes_key, aes_iv = calc_key(session.auth_key.key, msg_key, False)
data = BinaryReader(AES.decrypt_ige(body[24:], aes_key, aes_iv))
data.read_long() # remote_salt
if data.read_long() != session.id:
raise SecurityError('Server replied with a wrong session ID')
remote_msg_id = data.read_long()
remote_sequence = data.read_int()
msg_len = data.read_int()
message = data.read(msg_len)
# https://core.telegram.org/mtproto/security_guidelines
# Sections "checking sha256 hash" and "message length"
if msg_key != sha256(
session.auth_key.key[96:96 + 32] + data.get_bytes()).digest()[8:24]:
raise SecurityError("Received msg_key doesn't match with expected one")
return message, remote_msg_id, remote_sequence
def calc_key(auth_key, msg_key, client):
"""
Calculate the key based on Telegram guidelines
for MtProto 2, specifying whether it's the client or not.
"""
# https://core.telegram.org/mtproto/description#defining-aes-key-and-initialization-vector
x = 0 if client else 8
sha256a = sha256(msg_key + auth_key[x: x + 36]).digest()
sha256b = sha256(auth_key[x + 40:x + 76] + msg_key).digest()
aes_key = sha256a[:8] + sha256b[8:24] + sha256a[24:32]
aes_iv = sha256b[:8] + sha256a[8:24] + sha256b[24:32]
return aes_key, aes_iv
def generate_key_data_from_nonce(server_nonce, new_nonce):
"""Generates the key data corresponding to the given nonce"""
server_nonce = server_nonce.to_bytes(16, 'little', signed=True)