Techras

Twin Oracle

Category	Difficulty	Score	Solves	First 🩸
Crypto	Baby 👶	29	301	G3

Code / Description

I'm having trouble determining when to discard a number versus when to reuse it in Techras. Any advice would be helpful!

#!/usr/bin/env python3

from Crypto.Util.number import *
from string import *
from flag import flag

def pad(flag):
    r = len(flag) % 8
    if r != 0:
        flag = flag[:-1] + (8 - r) * printable[:63][getRandomRange(0, 62)].encode() + flag[-1:]
    return flag

def genkey(nbit):
    p, q = [getPrime(nbit) for _ in ':)']
    n = p * q
    return n, (p, q)

def encrypt(msg, pubkey):
    msg = pad(msg)
    e = getPrime(32)
    m = bytes_to_long(msg)
    c = pow(m, e, pubkey)
    return str(c) + str(e)

nbit = 1024
pubkey, _ = genkey(nbit)

print(f'n = {pubkey}')
for _ in range(110):
    print(f'c = {encrypt(flag, pubkey)}')

Overview

Challenge Analysis

Solution

Final Code

Flag

ASIS{d0nT___rEuS3___peXp!}

Authors

Kourosh Rajabzadeh