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mtproto.py
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mtproto.py
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# -*- coding: utf-8 -*-
"""
Created on Tue Sep 2 19:26:15 2014
@author: Anton Grigoryev
@author: Sammy Pfeiffer
"""
from binascii import crc32 as originalcrc32
from time import time
import io
import os.path
import socket
import struct
# pycrypto module
from Crypto.Hash import SHA
from Crypto.PublicKey import RSA
from Crypto.Util.strxor import strxor
from Crypto.Util.number import long_to_bytes, bytes_to_long
# local modules
import crypt
import prime
import TL
def crc32(data):
return originalcrc32(data) & 0xffffffff
def vis(bs):
"""
Function to visualize byte streams. Split into bytes, print to console.
:param bs: BYTE STRING
"""
bs = bytearray(bs)
symbols_in_one_line = 8
n = len(bs) // symbols_in_one_line
i = 0
for i in range(n):
print(str(i*symbols_in_one_line)+" | "+" ".join(["%02X" % b for b in bs[i*symbols_in_one_line:(i+1)*symbols_in_one_line]])) # for every 8 symbols line
if not len(bs) % symbols_in_one_line == 0:
print(str((i+1)*symbols_in_one_line)+" | "+" ".join(["%02X" % b for b in bs[(i+1)*symbols_in_one_line:]])+"\n") # for last line
class Session:
""" Manages TCP Transport. encryption and message frames """
def __init__(self, ip, port, auth_key=None, server_salt=None):
# creating socket
self.sock = socket.socket()
self.sock.connect((ip, port))
self.number = 0
self.timedelta = 0
self.session_id = os.urandom(8)
self.auth_key = auth_key
self.auth_key_id = SHA.new(self.auth_key).digest()[-8:] if self.auth_key else None
self.sock.settimeout(5.0)
self.MAX_RETRY = 5;
self.AUTH_MAX_RETRY = 5;
def __del__(self):
# closing socket when session object is deleted
self.sock.close()
def send_message(self, message_data):
"""
Forming the message frame and sending message to server
:param message: byte string to send
"""
message_id = struct.pack('<Q', int((time()+self.timedelta)*2**30)*4)
if self.auth_key is None or self.server_salt is None:
# Unencrypted data send
message = (b'\x00\x00\x00\x00\x00\x00\x00\x00' +
message_id +
struct.pack('<I', len(message_data)) +
message_data)
else:
# Encrypted data send
encrypted_data = (self.server_salt +
self.session_id +
message_id +
struct.pack('<II', self.number, len(message_data)) +
message_data)
message_key = SHA.new(encrypted_data).digest()[-16:]
padding = os.urandom((-len(encrypted_data)) % 16)
print(len(encrypted_data+padding))
aes_key, aes_iv = self.aes_calculate(message_key)
message = (self.auth_key_id + message_key +
crypt.ige_encrypt(encrypted_data+padding, aes_key, aes_iv))
step1 = struct.pack('<II', len(message)+12, self.number) + message
step2 = step1 + struct.pack('<I', crc32(step1))
self.sock.send(step2)
self.number += 1
def recv_message(self):
"""
Reading socket and receiving message from server. Check the CRC32.
"""
packet_length_data = self.sock.recv(4) # reads how many bytes to read
if len(packet_length_data) < 4:
raise Exception("Nothing in the socket!")
packet_length = struct.unpack("<I", packet_length_data)[0]
packet = self.sock.recv(packet_length - 4) # read the rest of bytes from socket
# check the CRC32
if not crc32(packet_length_data + packet[0:-4]) == struct.unpack('<I', packet[-4:])[0]:
raise Exception("CRC32 was not correct!")
x = struct.unpack("<I", packet[:4])
auth_key_id = packet[4:12]
if auth_key_id == b'\x00\x00\x00\x00\x00\x00\x00\x00':
# No encryption - Plain text
(message_id, message_length) = struct.unpack("<8sI", packet[12:24])
data = packet[24:24+message_length]
elif auth_key_id == self.auth_key_id:
message_key = packet[12:28]
encrypted_data = packet[28:-4]
aes_key, aes_iv = self.aes_calculate(message_key, direction="from server")
decrypted_data = crypt.ige_decrypt(encrypted_data, aes_key, aes_iv)
assert decrypted_data[0:8] == self.server_salt
assert decrypted_data[8:16] == self.session_id
message_id = decrypted_data[16:24]
seq_no = struct.unpack("<I", decrypted_data[24:28])[0]
message_data_length = struct.unpack("<I", decrypted_data[28:32])[0]
data = decrypted_data[32:32+message_data_length]
else:
raise Exception("Got unknown auth_key id")
return data
def method_call(self, method, **kwargs):
for i in range(1, self.MAX_RETRY):
try:
self.send_message(TL.serialize_method(method, **kwargs))
server_answer = self.recv_message()
except socket.timeout:
print("Retry call method")
continue
return TL.deserialize(io.BytesIO(server_answer))
def create_auth_key(self):
nonce = os.urandom(16)
print("Requesting pq")
ResPQ = self.method_call('req_pq', nonce=nonce)
server_nonce = ResPQ['server_nonce']
# TODO: selecting RSA public key based on this fingerprint
public_key_fingerprint = ResPQ['server_public_key_fingerprints'][0]
pq_bytes = ResPQ['pq']
pq = bytes_to_long(pq_bytes)
[p, q] = prime.primefactors(pq)
if p > q: (p, q) = (q, p)
assert p*q == pq and p < q
print("Factorization %d = %d * %d" % (pq, p, q))
p_bytes = long_to_bytes(p)
q_bytes = long_to_bytes(q)
f = open(os.path.join(os.path.dirname(__file__), "rsa.pub"))
key = RSA.importKey(f.read())
new_nonce = os.urandom(32)
data = TL.serialize_obj('p_q_inner_data',
pq=pq_bytes,
p=p_bytes,
q=q_bytes,
nonce=nonce,
server_nonce=server_nonce,
new_nonce=new_nonce)
sha_digest = SHA.new(data).digest()
random_bytes = os.urandom(255-len(data)-len(sha_digest))
to_encrypt = sha_digest + data + random_bytes
encrypted_data = key.encrypt(to_encrypt, 0)[0]
print("Starting Diffie Hellman key exchange")
server_dh_params = self.method_call('req_DH_params',
nonce=nonce,
server_nonce=server_nonce,
p=p_bytes,
q=q_bytes,
public_key_fingerprint=public_key_fingerprint,
encrypted_data=encrypted_data)
assert nonce == server_dh_params['nonce']
assert server_nonce == server_dh_params['server_nonce']
encrypted_answer = server_dh_params['encrypted_answer']
tmp_aes_key = SHA.new(new_nonce + server_nonce).digest() + SHA.new(server_nonce + new_nonce).digest()[0:12]
tmp_aes_iv = SHA.new(server_nonce + new_nonce).digest()[12:20] + SHA.new(new_nonce + new_nonce).digest() + new_nonce[0:4]
answer_with_hash = crypt.ige_decrypt(encrypted_answer, tmp_aes_key, tmp_aes_iv)
answer_hash = answer_with_hash[:20]
answer = answer_with_hash[20:]
# TODO: SHA hash assertion here
server_DH_inner_data = TL.deserialize(io.BytesIO(answer))
assert nonce == server_DH_inner_data['nonce']
assert server_nonce == server_DH_inner_data['server_nonce']
dh_prime_str = server_DH_inner_data['dh_prime']
g = server_DH_inner_data['g']
g_a_str = server_DH_inner_data['g_a']
server_time = server_DH_inner_data['server_time']
self.timedelta = server_time - time()
print("Server-client time delta = %.1f s" % self.timedelta)
dh_prime = bytes_to_long(dh_prime_str)
g_a = bytes_to_long(g_a_str)
assert prime.isprime(dh_prime)
retry_id = 0
b_str = os.urandom(256)
b = bytes_to_long(b_str)
g_b = pow(g, b, dh_prime)
g_b_str = long_to_bytes(g_b)
data = TL.serialize_obj('client_DH_inner_data',
nonce=nonce,
server_nonce=server_nonce,
retry_id=retry_id,
g_b=g_b_str)
data_with_sha = SHA.new(data).digest()+data
data_with_sha_padded = data_with_sha + os.urandom(-len(data_with_sha) % 16)
encrypted_data = crypt.ige_encrypt(data_with_sha_padded, tmp_aes_key, tmp_aes_iv)
for i in range(1, self.AUTH_MAX_RETRY): # retry when dh_gen_retry or dh_gen_fail
Set_client_DH_params_answer = self.method_call('set_client_DH_params',
nonce=nonce,
server_nonce=server_nonce,
encrypted_data=encrypted_data)
# print Set_client_DH_params_answer
auth_key = pow(g_a, b, dh_prime)
auth_key_str = long_to_bytes(auth_key)
auth_key_sha = SHA.new(auth_key_str).digest()
auth_key_aux_hash = auth_key_sha[:8]
new_nonce_hash1 = SHA.new(new_nonce+b'\x01'+auth_key_aux_hash).digest()[-16:]
new_nonce_hash2 = SHA.new(new_nonce+b'\x02'+auth_key_aux_hash).digest()[-16:]
new_nonce_hash3 = SHA.new(new_nonce+b'\x03'+auth_key_aux_hash).digest()[-16:]
assert Set_client_DH_params_answer['nonce'] == nonce
assert Set_client_DH_params_answer['server_nonce'] == server_nonce
if Set_client_DH_params_answer.name == 'dh_gen_ok':
assert Set_client_DH_params_answer['new_nonce_hash1'] == new_nonce_hash1
print("Diffie Hellman key exchange processed successfully")
self.server_salt = strxor(new_nonce[0:8], server_nonce[0:8])
self.auth_key = auth_key_str
self.auth_key_id = auth_key_sha[-8:]
print("Auth key generated")
return "Auth Ok"
elif Set_client_DH_params_answer.name == 'dh_gen_retry':
assert Set_client_DH_params_answer['new_nonce_hash2'] == new_nonce_hash2
print ("Retry Auth")
elif Set_client_DH_params_answer.name == 'dh_gen_fail':
assert Set_client_DH_params_answer['new_nonce_hash3'] == new_nonce_hash3
print("Auth Failed")
raise Exception("Auth Failed")
else: raise Exception("Response Error")
def aes_calculate(self, msg_key, direction="to server"):
x = 0 if direction == "to server" else 8
sha1_a = SHA.new(msg_key + self.auth_key[x:x+32]).digest()
sha1_b = SHA.new(self.auth_key[x+32:x+48] + msg_key + self.auth_key[48+x:64+x]).digest()
sha1_c = SHA.new(self.auth_key[x+64:x+96] + msg_key).digest()
sha1_d = SHA.new(msg_key + self.auth_key[x+96:x+128]).digest()
aes_key = sha1_a[0:8] + sha1_b[8:20] + sha1_c[4:16]
aes_iv = sha1_a[8:20] + sha1_b[0:8] + sha1_c[16:20] + sha1_d[0:8]
return aes_key, aes_iv