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from hashlib import sha256
import random
from Crypto.Util.number import *
import os
from Crypto.Cipher import AES
from Crypto.Util.Padding import pad, unpad
with open("/home/ctf/flag", "r") as f:
flag = f.read().strip().encode()
class prng:
def __init__(self, seed, a, b, c, d, e, p):
self.state = seed
self.a = a
self.b = b
self.c = c
self.d = d
self.e = e
self.p = p
def next(self, i):
if i % 2 == 0:
self.state = (self.a * self.state**2 + self.b * self.state + self.c) % self.p
else:
self.state = (self.d * self.state + self.e) % self.p
return self.state
def show(self):
return (self.a, self.b, self.c, self.d, self.e, self.p)
p = getPrime(256)
[a, b, c, d, e] = [random.randint(1, p) for _ in range(5)]
logo = '''
█ █ █████ █ █ █████ ███████ ███████
█ █ ░ █ ░░░░░ █░ █░ █ ░░░░░ ░░█░░░░ █░░░░░░░
█ █ ░ ░█░ ░░░░░ █░░█ █░░█░ ░░░░░ ░█░░░░░█░░░░░░░░
█ ░ ░ ░█████░░░█░░█░ █░░█░░ ░░░░░ █░░░░░█████░░░░░
█ █ ░ ░ ░░░░█ █░█░█░█░░█░░░ █░░░ █░░░░░█ ░ █ ░ ░░░█░ ██░░ ██░░█░░░ █░░░ █░░░░░░ █ ░ ░ █ █████░░░█░░░░ █░░░█████ █░░░ █░░░░░░░
░ ░ ░ ░ ░░░░░ ░░░░░ ░ ░░░ ░░░░░ ░░░ ░░░
░ ░ ░ ░░░░░ ░ ░░░ ░░ ░░░░░ ░░ ░░
░ ░ ░░░░░ ░ ░ ░░░░░ ░ ░ '''
menu = '''
[1] Show PRNG parameters
[2] Give me your seed
[3] Generate Challenge
[4] Exit
'''
if __name__ == "__main__":
print(logo)
while True:
print(menu)
choice = input("Your choice: ")
if choice == '1':
print(f"PRNG parameters:\na = {a}\nb = {b}\nc = {c}\nd = {d}\ne = {e}\np = {p}\n")
elif choice == '2':
seed_input = input("Enter your seed (integer): ")
try:
user_seed = int(seed_input)
user_prng = prng(user_seed, a, b, c, d, e, p)
print("Seed accepted!\n")
except ValueError:
print("Invalid seed. Please enter an integer.\n")
elif choice == '3':
if 'user_prng' not in locals():
print("Please provide your seed first (option 2).\n")
continue
tmp = user_seed
rng = random.Random()
rng.seed(os.urandom(16))
gift = []
for i in range(320):
random_number = rng.getrandbits(256)
usr_number = user_prng.next(i)
if usr_number == tmp:
gift.append(random_number)
key = long_to_bytes(rng.getrandbits(128))
cipher = AES.new(key, AES.MODE_ECB)
c = cipher.encrypt(pad(flag, 16))
print(f"Encrypted flag (hex): {c.hex()}")
print(f"gift = {gift}\n")
break
elif choice == '4':
print("Exiting. Goodbye!")
break
else:
print("Invalid choice. Please try again.\n")
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