MeePwn CTF Final 2018 - Fake Prince

fake_prince.py

#!/usr/bin/env python2

from gmpy2 import powmod, is_prime
from flag import FLAG
import sys
from hashlib import sha256
from os import urandom
import sys

def write_to_file(num):
    f = open('number.log', 'a+')
    f.write('{}\n'.format(num))


pow = powmod

# -------------------------------------------------------------

strong_primes = [2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293]


def rabmil(n):
    if n & 1 == 0:
        return False
    else:
        s, d = 0, n - 1
        while d & 1 == 0:
            s, d = s + 1, d >> 1
        for a in strong_primes:
            x = pow(a, d, n)
            if x != 1 and x + 1 != n:
                for r in range(1, s):
                    x = pow(x, 2, n)
                    if x == 1:
                        return False
                    elif x == n - 1:
                        a = 0
                        break
                if a:
                    return False
        return True
# -------------------------------------------------------------

def proof_of_shit():
    """
    This function has very special purpose 
    :)) Simply to screw you up
    """
    raw = urandom(6)
    print 'prefix = {}'.format(raw.encode('hex'))
    print('Challenge: ')
    sys.stdout.flush()
    challenge = sys.stdin.readline().strip()
    temp = sha256(raw + challenge).hexdigest()
    if temp.startswith('25455'):
        return True
    else:
        return False



if __name__ == '__main__':
    if proof_of_shit():

        introduction = """
        This time, the challenge is my redemption. 
        Have fun.! It just a warm up challenge.

        """
        print introduction

        try:
            print ' p: ',
            sys.stdout.flush()

            num = int(sys.stdin.readline().strip())
            write_to_file(num)
            if rabmil(num) == True and is_prime(num) == False:
                print '\n Congratz! I give you my thumb up if you solve this. \n'
                print FLAG
            else:
                print "\n Try harder."

        except:
            print "Take your time to think of the inputs."
            pass

        sys.exit(0)
    
    else:
        print "Nah."
        sys.exit(1)