Telethon/network/authenticator.py

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import os
import time
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import utils
from utils import BinaryWriter, BinaryReader
from crypto import AES, AuthKey, Factorizator, RSA
from network import MtProtoPlainSender
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def do_authentication(transport):
"""Executes the authentication process with the Telegram servers.
If no error is rose, returns both the authorization key and the time offset"""
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sender = MtProtoPlainSender(transport)
# Step 1 sending: PQ Request
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nonce = os.urandom(16)
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with BinaryWriter() as writer:
writer.write_int(0x60469778, signed=False) # Constructor number
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writer.write(nonce)
sender.send(writer.get_bytes())
# Step 1 response: PQ Request
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pq, pq_bytes, server_nonce, fingerprints = None, None, None, []
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with BinaryReader(sender.receive()) as reader:
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response_code = reader.read_int(signed=False)
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if response_code != 0x05162463:
raise AssertionError('Invalid response code: {}'.format(hex(response_code)))
nonce_from_server = reader.read(16)
if nonce_from_server != nonce:
raise AssertionError('Invalid nonce from server')
server_nonce = reader.read(16)
pq_bytes = reader.tgread_bytes()
pq = get_int(pq_bytes)
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vector_id = reader.read_int()
if vector_id != 0x1cb5c415:
raise AssertionError('Invalid vector constructor ID: {}'.format(hex(response_code)))
fingerprints = []
fingerprint_count = reader.read_int()
for _ in range(fingerprint_count):
fingerprints.append(reader.read(8))
# Step 2 sending: DH Exchange
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new_nonce = os.urandom(32)
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p, q = Factorizator.factorize(pq)
with BinaryWriter() as pq_inner_data_writer:
pq_inner_data_writer.write_int(0x83c95aec, signed=False) # PQ Inner Data
pq_inner_data_writer.tgwrite_bytes(get_byte_array(pq, signed=False))
pq_inner_data_writer.tgwrite_bytes(get_byte_array(min(p, q), signed=False))
pq_inner_data_writer.tgwrite_bytes(get_byte_array(max(p, q), signed=False))
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pq_inner_data_writer.write(nonce)
pq_inner_data_writer.write(server_nonce)
pq_inner_data_writer.write(new_nonce)
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cipher_text, target_fingerprint = None, None
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for fingerprint in fingerprints:
cipher_text = RSA.encrypt(get_fingerprint_text(fingerprint), pq_inner_data_writer.get_bytes())
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if cipher_text is not None:
target_fingerprint = fingerprint
break
if cipher_text is None:
raise AssertionError('Could not find a valid key for fingerprints: {}'
.format(', '.join([get_fingerprint_text(f) for f in fingerprints])))
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with BinaryWriter() as req_dh_params_writer:
req_dh_params_writer.write_int(0xd712e4be, signed=False) # Req DH Params
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req_dh_params_writer.write(nonce)
req_dh_params_writer.write(server_nonce)
req_dh_params_writer.tgwrite_bytes(get_byte_array(min(p, q), signed=False))
req_dh_params_writer.tgwrite_bytes(get_byte_array(max(p, q), signed=False))
req_dh_params_writer.write(target_fingerprint)
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req_dh_params_writer.tgwrite_bytes(cipher_text)
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req_dh_params_bytes = req_dh_params_writer.get_bytes()
sender.send(req_dh_params_bytes)
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# Step 2 response: DH Exchange
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encrypted_answer = None
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with BinaryReader(sender.receive()) as reader:
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response_code = reader.read_int(signed=False)
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if response_code == 0x79cb045d:
raise AssertionError('Server DH params fail: TODO')
if response_code != 0xd0e8075c:
raise AssertionError('Invalid response code: {}'.format(hex(response_code)))
nonce_from_server = reader.read(16)
if nonce_from_server != nonce:
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raise NotImplementedError('Invalid nonce from server')
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server_nonce_from_server = reader.read(16)
if server_nonce_from_server != server_nonce:
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raise NotImplementedError('Invalid server nonce from server')
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encrypted_answer = reader.tgread_bytes()
# Step 3 sending: Complete DH Exchange
key, iv = utils.generate_key_data_from_nonces(server_nonce, new_nonce)
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plain_text_answer = AES.decrypt_ige(encrypted_answer, key, iv)
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g, dh_prime, ga, time_offset = None, None, None, None
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with BinaryReader(plain_text_answer) as dh_inner_data_reader:
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hashsum = dh_inner_data_reader.read(20)
code = dh_inner_data_reader.read_int(signed=False)
if code != 0xb5890dba:
raise AssertionError('Invalid DH Inner Data code: {}'.format(code))
nonce_from_server1 = dh_inner_data_reader.read(16)
if nonce_from_server1 != nonce:
raise AssertionError('Invalid nonce in encrypted answer')
server_nonce_from_server1 = dh_inner_data_reader.read(16)
if server_nonce_from_server1 != server_nonce:
raise AssertionError('Invalid server nonce in encrypted answer')
g = dh_inner_data_reader.read_int()
dh_prime = get_int(dh_inner_data_reader.tgread_bytes(), signed=False)
ga = get_int(dh_inner_data_reader.tgread_bytes(), signed=False)
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server_time = dh_inner_data_reader.read_int()
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time_offset = server_time - int(time.time())
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b = get_int(os.urandom(2048), signed=False)
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gb = pow(g, b, dh_prime)
gab = pow(ga, b, dh_prime)
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# Prepare client DH Inner Data
with BinaryWriter() as client_dh_inner_data_writer:
client_dh_inner_data_writer.write_int(0x6643b654, signed=False) # Client DH Inner Data
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client_dh_inner_data_writer.write(nonce)
client_dh_inner_data_writer.write(server_nonce)
client_dh_inner_data_writer.write_long(0) # TODO retry_id
client_dh_inner_data_writer.tgwrite_bytes(get_byte_array(gb, signed=False))
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with BinaryWriter() as client_dh_inner_data_with_hash_writer:
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client_dh_inner_data_with_hash_writer.write(utils.sha1(client_dh_inner_data_writer.get_bytes()))
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client_dh_inner_data_with_hash_writer.write(client_dh_inner_data_writer.get_bytes())
client_dh_inner_data_bytes = client_dh_inner_data_with_hash_writer.get_bytes()
# Encryption
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client_dh_inner_data_encrypted_bytes = AES.encrypt_ige(client_dh_inner_data_bytes, key, iv)
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# Prepare Set client DH params
with BinaryWriter() as set_client_dh_params_writer:
set_client_dh_params_writer.write_int(0xf5045f1f, signed=False)
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set_client_dh_params_writer.write(nonce)
set_client_dh_params_writer.write(server_nonce)
set_client_dh_params_writer.tgwrite_bytes(client_dh_inner_data_encrypted_bytes)
set_client_dh_params_bytes = set_client_dh_params_writer.get_bytes()
sender.send(set_client_dh_params_bytes)
# Step 3 response: Complete DH Exchange
with BinaryReader(sender.receive()) as reader:
code = reader.read_int(signed=False)
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if code == 0x3bcbf734: # DH Gen OK
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nonce_from_server = reader.read(16)
if nonce_from_server != nonce:
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raise NotImplementedError('Invalid nonce from server')
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server_nonce_from_server = reader.read(16)
if server_nonce_from_server != server_nonce:
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raise NotImplementedError('Invalid server nonce from server')
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new_nonce_hash1 = reader.read(16)
auth_key = AuthKey(get_byte_array(gab, signed=False))
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new_nonce_hash_calculated = auth_key.calc_new_nonce_hash(new_nonce, 1)
if new_nonce_hash1 != new_nonce_hash_calculated:
raise AssertionError('Invalid new nonce hash')
return auth_key, time_offset
elif code == 0x46dc1fb9: # DH Gen Retry
raise NotImplementedError('dh_gen_retry')
elif code == 0xa69dae02: # DH Gen Fail
raise NotImplementedError('dh_gen_fail')
else:
raise AssertionError('DH Gen unknown: {}'.format(hex(code)))
def get_fingerprint_text(fingerprint):
"""Gets a fingerprint text in 01-23-45-67-89-AB-CD-EF format (no hyphens)"""
return ''.join(hex(b)[2:].rjust(2, '0').upper() for b in fingerprint)
# The following methods operate in big endian (unlike most of Telegram API) because:
# > "...pq is a representation of a natural number (in binary *big endian* format)..."
# > "...current value of dh_prime equals (in *big-endian* byte order)..."
# Reference: https://core.telegram.org/mtproto/auth_key
def get_byte_array(integer, signed):
"""Gets the arbitrary-length byte array corresponding to the given integer"""
bits = integer.bit_length()
byte_length = (bits + 8 - 1) // 8 # 8 bits per byte
return int.to_bytes(integer, length=byte_length, byteorder='big', signed=signed)
def get_int(byte_array, signed=True):
"""Gets the specified integer from its byte array. This should be used by the authenticator,
who requires the data to be in big endian"""
return int.from_bytes(byte_array, byteorder='big', signed=signed)