Telethon/crypto/rsa.py

# This file is based on TLSharp
# https://github.com/sochix/TLSharp/blob/master/TLSharp.Core/MTProto/Crypto/RSA.cs
import utils
from utils import BinaryWriter


class RSAServerKey:
    def __init__(self, fingerprint, m, e):
        self.fingerprint = fingerprint
        self.m = m
        self.e = e

    def encrypt(self, data, offset=None, length=None):
        """Encrypts the given data with the current key"""
        if offset is None:
            offset = 0
        if length is None:
            length = len(data)

        with BinaryWriter() as writer:
            # Write SHA
            writer.write(utils.sha1(data[offset:offset+length]))
            # Write data
            writer.write(data[offset:offset+length])
            # Add padding if required
            if length < 235:
                writer.write(utils.generate_random_bytes(235 - length))

            cipher_text = utils.get_byte_array(
                pow(int.from_bytes(writer.get_bytes(), byteorder='big'), self.e, self.m),
                signed=False)

            if len(cipher_text) == 256:
                return cipher_text

            else:
                padding = bytes(256 - len(cipher_text))
                return padding + cipher_text


class RSA:
    _server_keys = {
        '216be86c022bb4c3':
            RSAServerKey('216be86c022bb4c3', int('C150023E2F70DB7985DED064759CFECF0AF328E69A41DAF4D6F01B538135A6F9'
                                                 '1F8F8B2A0EC9BA9720CE352EFCF6C5680FFC424BD634864902DE0B4BD6D49F4E'
                                                 '580230E3AE97D95C8B19442B3C0A10D8F5633FECEDD6926A7F6DAB0DDB7D457F'
                                                 '9EA81B8465FCD6FFFEED114011DF91C059CAEDAF97625F6C96ECC74725556934'
                                                 'EF781D866B34F011FCE4D835A090196E9A5F0E4449AF7EB697DDB9076494CA5F'
                                                 '81104A305B6DD27665722C46B60E5DF680FB16B210607EF217652E60236C255F'
                                                 '6A28315F4083A96791D7214BF64C1DF4FD0DB1944FB26A2A57031B32EEE64AD1'
                                                 '5A8BA68885CDE74A5BFC920F6ABF59BA5C75506373E7130F9042DA922179251F',
                                                 16), int('010001', 16))
    }

    @staticmethod
    def encrypt(fingerprint, data, offset=None, length=None):
        """Encrypts the given data given a fingerprint"""
        if fingerprint.lower() not in RSA._server_keys:
            return None

        key = RSA._server_keys[fingerprint.lower()]
        return key.encrypt(data, offset, length)