2016/asis-ctf/rsa/rsa.py

#!/usr/bin/python

import gmpy
from Crypto.Util.number import *
from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_v1_5

flag = open('flag', 'r').read() * 30

def ext_rsa_encrypt(p, q, e, msg):
    m = bytes_to_long(msg)
    while True:
        n = p * q
        try:
            phi = (p - 1)*(q - 1)
            d = gmpy.invert(e, phi)
            pubkey = RSA.construct((long(n), long(e)))
            key = PKCS1_v1_5.new(pubkey)
            enc = key.encrypt(msg).encode('base64')
            return enc
        except:
            p = gmpy.next_prime(p**2 + q**2)
            q = gmpy.next_prime(2*p*q)
            e = gmpy.next_prime(e**2)

p = getPrime(128)
q = getPrime(128)
n = p*q
e = getPrime(64)
pubkey = RSA.construct((long(n), long(e)))
f = open('pubkey.pem', 'w')
f.write(pubkey.exportKey())
g = open('flag.enc', 'w')
g.write(ext_rsa_encrypt(p, q, e, flag))