WeChall - Impossible n'est pas français

Challenge

题目要求将一个 170+ 位的大整数分解质因数，限时 6 秒。

Solution

直接分解这么大的数是不现实的。但题目有一个关键缺陷：提交错误答案后，服务器会在错误信息中泄露正确的答案，并且挑战数字保持不变。

所以解法分三步：

1. 请求一个新数字
2. 提交任意错误答案（如 solution=1）→ 服务器返回 Correct would have been "xxx"
3. 用泄露的正确答案重新提交

import requests, re

cookies = {'WC': 'YOUR_WECHALL_COOKIE'}
base = 'https://www.wechall.net/en/challenge/impossible/index.php'

# Step 1: request new number
r = requests.get(f'{base}?request=new_number', cookies=cookies)
csrf = re.search(r'name="gwf3_csrf" value="([^"]+)"', r.text).group(1)

# Step 2: submit wrong answer to leak the correct one
r2 = requests.post(base, data={
    'solution': '1',
    'solve': 'Submit',
    'gwf3_csrf': csrf
}, cookies=cookies)
correct = re.search(r'Correct would have been "(\d+)"', r2.text).group(1)

# Step 3: submit the correct answer
r3 = requests.post(base, data={
    'solution': correct,
    'solve': 'Submit',
    'gwf3_csrf': csrf
}, cookies=cookies)

print("Solved!" if 'correct' in r3.text.lower() else "Failed")