HTB CTF 2024 - Vault Of Hope - Crypto - eXciting Outpost Recon Solution

Hijacking the outpost responsible for housing the messengers of the core gangs, we have managed to intercept communications between a newly-elected leader and the Tariaki, a well-established and powerful gang. In an attempt to sow conflict and prevent the creation of a singular all-powerful coalition to oppress the common people, we want YOU to use this message to our advantage. Can you use their obsequiousness to your advantage?

Difficulty: very easy

Challenge File(s) Download

File Contents

Encryption code located in source.py

from hashlib import sha256

import os

LENGTH = 32


def encrypt_data(data, k):
    data += b'\x00' * (-len(data) % LENGTH)
    encrypted = b''

    for i in range(0, len(data), LENGTH):
        chunk = data[i:i+LENGTH]

        for a, b in zip(chunk, k):
            encrypted += bytes([a ^ b])

        k = sha256(k).digest()

    return encrypted


key = os.urandom(32)

with open('plaintext.txt', 'rb') as f:
    plaintext = f.read()

assert plaintext.startswith(b'Great and Noble Leader of the Tariaki')       # have to make sure we are aptly sycophantic

with open('output.txt', 'w') as f:
    enc = encrypt_data(plaintext, key)
    f.write(enc.hex())