Initialization

CHALLENGE DESCRIPTION

VERY EASY

During a cyber security audit of your government's infrastructure, you discover log entries showing traffic directed towards an IP address within the enemy territory of "Oumara". This alarming revelation triggers suspicion of a mole within Lusons' government. Determined to unveil the truth, you analyze the encryption scheme with the goal of breaking it and decrypting the suspicious communication. Your objective is to extract vital information and gather intelligence, ultimately protecting your nation from potential threats.

source.py

#!/usr/bin/env python3

import os
from Crypto.Util import Counter
from Crypto.Util.Padding import pad
from Crypto.Cipher import AES

class AdvancedEncryption:
    def __init__(self, block_size):
        self.KEYS = self.generate_encryption_keys()
        self.CTRs = [Counter.new(block_size) for i in range(len(MSG))] # nonce reuse : avoided!

    def generate_encryption_keys(self):
        keys = [[b'\x00']*16] * len(MSG)
        for i in range(len(keys)):
            for j in range(len(keys[i])):
                keys[i][j] = os.urandom(1)
        return keys

    def encrypt(self, i, msg):
        key = b''.join(self.KEYS[i])
        ctr = self.CTRs[i]
        cipher = AES.new(key, AES.MODE_CTR, counter=ctr)
        return cipher.encrypt(pad(msg.encode(), 16))

def main():
    AE = AdvancedEncryption(128)
    with open('output.txt', 'w') as f:
        for i in range(len(MSG)):
            ct = AE.encrypt(i, MSG[i])
            f.write(ct.hex()+'\n')

if __name__ == '__main__':
    with open('messages.txt') as f:
        MSG = eval(f.read())
    main()

messages.txt

[
    'This is some public information that can be read out loud.',
    'No one can crack our encryption algorithm.',
    'HTB{?????????????????????????????????????????????}',
    'Secret information is encrypted with Advanced Encryption Standards.',
]

看起来就是实现了一个 AES 加密逻辑，尝试编写解密脚本

from pwn import unhex, xor

P = [i.strip() for i in open("messages.txt", "r").read()[1:-2].replace(",", "").strip().split("'") if i.strip() != ""]

C = open("output.txt", "r").read().splitlines()

res = xor(unhex(C[2]), unhex(C[3]), P[3].encode())

res = "".join([chr(i) for i in res if i in range(0, 127)])

res = res[0 : res.find("}") + 1]

print(res)

Flag

HTB{d4mn_th3s3_ins3cur3_bl0ckch41n_p4r4m3t3rs!!!!}