HackTheBox FastJson and Furious Writeup

Explore the basics of cybersecurity in the FastJson and Furious Challenge on Hack The Box. This easy-level Challenge introduces encryption reversal and file handling concepts in a clear and accessible way, perfect for beginners.

import hashlib
import json

POSTFIX = "20240227"

def calc_hash(input_str):
    result_str = ""
    try:
        json_obj = json.loads(input_str.replace('":', POSTFIX + '":'))
        if len(json_obj.keys()) != 2:
            return "Not has exactly 2 keys"
        sorted_keys = sorted(json_obj.keys())
        for key in sorted_keys:
            result_str += key + str(json_obj[key])
        md5_hash = hashlib.md5()
        md5_hash.update(result_str.lower().encode('utf-8'))
        big_integer = md5_hash.hexdigest()
        while len(big_integer) < 32:
            big_integer = "0" + big_integer
        return f"HTB{{{big_integer}}}"
    except json.JSONDecodeError:
        return "JSONDecodeError"

input_str = '{"example_key1":"example_value1","example_key2":"example_value2"}'
input_str1 = '{"example_key1":"example_value1","example_key2":"example_value2"}'
#print(calc_hash(input_str1))
input_str2 = '{"@Type":"hhhkb.ctf.fastjson_and_furious.Flag","success":true}'
print(calc_hash(input_str2))

Summary

The FastJson and Furious Challenge on Hack The Box provides an accessible introduction to encryption reversal and file handling. This easy-level challenge is perfect for beginners, focusing on parsing JSON data and using MD5 hashing to derive a flag. The challenge walks through modifying JSON structures, understanding data handling, and applying basic encryption concepts, all while providing a fun and engaging problem-solving experience for newcomers to cybersecurity.