MTPyroger/pyrogram/session/auth.py

# Pyrogram - Telegram MTProto API Client Library for Python
# Copyright (C) 2017 Dan Tès <https://github.com/delivrance>
#
# This file is part of Pyrogram.
#
# Pyrogram is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Pyrogram is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with Pyrogram.  If not, see <http://www.gnu.org/licenses/>.

import logging
import time
from hashlib import sha1
from io import BytesIO
from os import urandom

from pyrogram.api import functions, types
from pyrogram.api.core import Object, Long, Int
from pyrogram.connection import Connection
from pyrogram.crypto import IGE, RSA, Prime
from .internals import MsgId, DataCenter

log = logging.getLogger(__name__)


# TODO: When using TCP connection mode, the server may close it at any time, causing the Auth key creation to fail
# The above is true when dealing with temporary keys, although for perm keys it didn't happened, yet.

class Auth:
    CURRENT_DH_PRIME = int(
        "C71CAEB9C6B1C9048E6C522F70F13F73980D40238E3E21C14934D037563D930F"
        "48198A0AA7C14058229493D22530F4DBFA336F6E0AC925139543AED44CCE7C37"
        "20FD51F69458705AC68CD4FE6B6B13ABDC9746512969328454F18FAF8C595F64"
        "2477FE96BB2A941D5BCD1D4AC8CC49880708FA9B378E3C4F3A9060BEE67CF9A4"
        "A4A695811051907E162753B56B0F6B410DBA74D8A84B2A14B3144E0EF1284754"
        "FD17ED950D5965B4B9DD46582DB1178D169C6BC465B0D6FF9CA3928FEF5B9AE4"
        "E418FC15E83EBEA0F87FA9FF5EED70050DED2849F47BF959D956850CE929851F"
        "0D8115F635B105EE2E4E15D04B2454BF6F4FADF034B10403119CD8E3B92FCC5B",
        16
    )

    def __init__(self, dc_id: int, test_mode: bool):
        self.dc_id = dc_id
        self.test_mode = test_mode

        self.connection = Connection(DataCenter(dc_id, test_mode))
        self.msg_id = MsgId()

    def pack(self, data: Object) -> bytes:
        return (
            bytes(8)
            + Long(self.msg_id())
            + Int(len(data.write()))
            + data.write()
        )

    @staticmethod
    def unpack(b: BytesIO):
        b.seek(20)  # Skip auth_key_id (8), message_id (8) and message_length (4)
        return Object.read(b)

    def send(self, data: Object):
        data = self.pack(data)
        self.connection.send(data)
        response = BytesIO(self.connection.recv())

        return self.unpack(response)

    def create(self):
        """
        https://core.telegram.org/mtproto/auth_key
        https://core.telegram.org/mtproto/samples-auth_key
        """
        log.info("Start creating a new auth key on DC{}".format(self.dc_id))

        self.connection.connect()

        # Step 1; Step 2
        nonce = int.from_bytes(urandom(16), "little", signed=True)
        log.debug("Send req_pq: {}".format(nonce))
        res_pq = self.send(functions.ReqPq(nonce))
        log.debug("Got ResPq: {}".format(res_pq.server_nonce))

        # Step 3
        pq = int.from_bytes(res_pq.pq, "big")
        log.debug("Start PQ factorization: {}".format(pq))
        start = time.time()
        g = Prime.decompose(pq)
        p, q = sorted((g, pq // g))  # p < q
        log.debug("Done PQ factorization ({}s): {} {}".format(round(time.time() - start, 3), p, q))

        # Step 4
        server_nonce = res_pq.server_nonce
        new_nonce = int.from_bytes(urandom(32), "little", signed=True)

        data = types.PQInnerData(
            res_pq.pq,
            int.to_bytes(p, 4, "big"),
            int.to_bytes(q, 4, "big"),
            nonce,
            server_nonce,
            new_nonce,
        ).write()

        sha = sha1(data).digest()
        padding = urandom(- (len(data) + len(sha)) % 255)
        data_with_hash = sha + data + padding
        encrypted_data = RSA.encrypt(data_with_hash, res_pq.server_public_key_fingerprints[0])

        log.debug("Done encrypt data with RSA")

        # Step 5. TODO: Handle "server_DH_params_fail". Code assumes response is ok
        log.debug("Send req_DH_params")
        server_dh_params = self.send(
            functions.ReqDhParams(
                nonce,
                server_nonce,
                int.to_bytes(p, 4, "big"),
                int.to_bytes(q, 4, "big"),
                res_pq.server_public_key_fingerprints[0],
                encrypted_data
            )
        )

        encrypted_answer = server_dh_params.encrypted_answer

        server_nonce = int.to_bytes(server_nonce, 16, "little", signed=True)
        new_nonce = int.to_bytes(new_nonce, 32, "little", signed=True)

        tmp_aes_key = (
            sha1(new_nonce + server_nonce).digest()
            + sha1(server_nonce + new_nonce).digest()[:12]
        )

        tmp_aes_iv = (
            sha1(server_nonce + new_nonce).digest()[12:]
            + sha1(new_nonce + new_nonce).digest() + new_nonce[:4]
        )

        server_nonce = int.from_bytes(server_nonce, "little", signed=True)

        answer_with_hash = IGE.decrypt(encrypted_answer, tmp_aes_key, tmp_aes_iv)
        answer = answer_with_hash[20:]

        server_dh_inner_data = Object.read(BytesIO(answer))

        log.debug("Done decrypting answer")

        dh_prime = int.from_bytes(server_dh_inner_data.dh_prime, "big")
        delta_time = server_dh_inner_data.server_time - time.time()

        log.debug("Delta time: {}".format(round(delta_time, 3)))

        # Step 6
        g = server_dh_inner_data.g
        b = int.from_bytes(urandom(256), "big")
        g_b = int.to_bytes(pow(g, b, dh_prime), 256, "big")

        retry_id = 0

        data = types.ClientDhInnerData(
            nonce,
            server_nonce,
            retry_id,
            g_b
        ).write()

        sha = sha1(data).digest()
        padding = urandom(- (len(data) + len(sha)) % 16)
        data_with_hash = sha + data + padding
        encrypted_data = IGE.encrypt(data_with_hash, tmp_aes_key, tmp_aes_iv)

        log.debug("Send set_client_DH_params")
        set_client_dh_params_answer = self.send(
            functions.SetClientDhParams(
                nonce,
                server_nonce,
                encrypted_data
            )
        )

        # TODO: Handle "auth_key_aux_hash" if the previous step fails

        # Step 7; Step 8
        g_a = int.from_bytes(server_dh_inner_data.g_a, "big")
        auth_key = int.to_bytes(pow(g_a, b, dh_prime), 256, "big")
        server_nonce = int.to_bytes(server_nonce, 16, "little", signed=True)

        # TODO: Handle errors

        #######################
        # Security checks
        #######################

        assert dh_prime == self.CURRENT_DH_PRIME
        log.debug("DH parameters check: OK")

        # https://core.telegram.org/mtproto/security_guidelines#g-a-and-g-b-validation
        g_b = int.from_bytes(g_b, "big")
        assert 1 < g < dh_prime - 1
        assert 1 < g_a < dh_prime - 1
        assert 1 < g_b < dh_prime - 1
        assert 2 ** (2048 - 64) < g_a < dh_prime - 2 ** (2048 - 64)
        assert 2 ** (2048 - 64) < g_b < dh_prime - 2 ** (2048 - 64)
        log.debug("g_a and g_b validation: OK")

        # https://core.telegram.org/mtproto/security_guidelines#checking-sha1-hash-values
        answer = server_dh_inner_data.write()  # Call .write() to remove padding
        assert answer_with_hash[:20] == sha1(answer).digest()
        log.debug("SHA1 hash values check: OK")

        # https://core.telegram.org/mtproto/security_guidelines#checking-nonce-server-nonce-and-new-nonce-fields
        # 1st message
        assert nonce == res_pq.nonce
        # 2nd message
        server_nonce = int.from_bytes(server_nonce, "little", signed=True)
        assert nonce == server_dh_params.nonce
        assert server_nonce == server_dh_params.server_nonce
        # 3rd message
        assert nonce == set_client_dh_params_answer.nonce
        assert server_nonce == set_client_dh_params_answer.server_nonce
        server_nonce = int.to_bytes(server_nonce, 16, "little", signed=True)
        log.debug("Nonce fields check: OK")

        # Step 9
        server_salt = IGE.xor(new_nonce[:8], server_nonce[:8])

        log.debug("Server salt: {}".format(int.from_bytes(server_salt, "little")))

        log.info(
            "Done auth key exchange: {}".format(
                set_client_dh_params_answer.__class__.__name__
            )
        )

        self.connection.close()

        return auth_key