a python script which can be used for cracking simple RSA ciphers with known public key

crackRSA.py

#!/usr/bin/env python3

import argparse
import requests
from Crypto.PublicKey import RSA
from Crypto.Util.number import long_to_bytes
from base64 import b64decode
import gmpy
import sys


def read_pubkey(filename):
    try:
        pubkey_b64 = open(filename).read()
        pubkey = b64decode(pubkey_b64)
        pub = RSA.importKey(pubkey)

        return pub

    except Exception as e:
        print('[!]' + str(e))
        sys.exit(1)


def init_parser():
    parser = argparse.ArgumentParser(description='Decrypt RSA message using public key')
    parser.add_argument('public_key', type=str, help='name of base64 encoded file containing public key')
    parser.add_argument('--message', type=str, help='enrypted message')
    parser.add_argument('--encfile', type=str, help='name of base64 encoded file containing encrypted message')
    parser.add_argument('-p', type=int, help='p factor')
    parser.add_argument('-q', type=int, help='q factor')

    return parser.parse_args()


def get_factors(n, args):
    if args.p and args.q:
        return int(args.p), int(args.q)

    res = requests.get('http://factordb.com/api', params={"query": (n)})
    factors = res.json()['factors']

    return int(factors[0][0]), int(factors[1][0])


def sanity_checks(n, e, p, q, d):
    print('[*] Checking n, p and q')
    assert  n == p * q
    print('[*] Checking d')
    assert 2 == pow(pow(2, e, n), d, n)


def get_message(args):
    message = ''

    if args.message:
        message = args.message

    if args.encfile:
        try:
            b64_msg = open(args.encfile).read()
            message = b64decode(b64_msg)
        except Exception as e:
            print('[!]' + str(e))

    data_int = int(message.hex(), 16)

    return data_int



if __name__ == '__main__':
    args = init_parser()
    print('[*] RSA decryption tool')
    print('[*] Written by h4ck1t')

    if not args.message and not args.encfile:
        print('What do you want do decrypt?')
        sys.exit(0)

    pub = read_pubkey(args.public_key)
    n = pub.n
    e = pub.e

    p, q = get_factors(n, args)

    d = gmpy.invert(e, (p-1)*(q-1))

    sanity_checks(n, e, p, q, d)

    data_int = get_message(args)
    data_decoded = pow(data_int, d, n)
    print('[*] Decoded data:')
    print(long_to_bytes(data_decoded))