changed 2 years ago  
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tags: writeup

ais3-2023

misc

welcome

打開pdf手動輸入

robot

手動計算

crypto

fernet

將ciphertext用base64 decode，即可取得經過fernet加密後的內容，再將前16個字元取出，則取得PBKDF2所需要的salt，後面字元則是加密內容，因此使用fernet.decrypt解密便可獲得明文。

import os
import base64
from cryptography.fernet import Fernet
from Crypto.Hash import SHA256
from Crypto.Protocol.KDF import PBKDF2
import re

myciphertext = b'iAkZMT9sfXIjD3yIpw0ldGdBQUFBQUJrVzAwb0pUTUdFbzJYeU0tTGQ4OUUzQXZhaU9HMmlOaC1PcnFqRUIzX0xtZXg0MTh1TXFNYjBLXzVBOVA3a0FaenZqOU1sNGhBcHR3Z21RTTdmN1dQUkcxZ1JaOGZLQ0E0WmVMSjZQTXN3Z252VWRtdXlaVW1fZ0pzV0xsaUM5VjR1ZHdj'
myciphertext=base64.b64decode(myciphertext)
salt=myciphertext[:16]
myciphertext=myciphertext[16:]

password = 'mysecretpassword'
key = PBKDF2(password.encode(), salt, 32, count=1000, hmac_hash_module=SHA256)  
f = Fernet(base64.urlsafe_b64encode(key))  

def decrypt(ciphertext):
    plaintext=f.decrypt(ciphertext).decode()
    return plaintext

plaintext = decrypt(myciphertext)
print(plaintext)

web

Login Panelb

  1. 在login page輸入
    Username: admin
    Password: ' OR 1=1 --
  2. 進入2fa頁面，然後修改網址2fa成dashboard
  3. 即可進入dashboard取得flag

結果

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