解题步骤

  1. 访问目标网页

    image-20210511170428315

  2. 题目描述：Can you encrypt fast enough?

  3. 检测Cookie，发现存在一个key为PHPSESSID的Cookie，将其删除之后刷新页面，虽然该Cookie重新生成了，但是值发生了改变，对其进行编解码均无明显特征

  4. 对网页上给出的字符串进行MD5散列，提交之后显示Too slow，而且刷新了要进行MD5散列的字符串

    image-20210511170838316

  5. 猜测可能通过请求体进行的时间判断，使用Burp Suite进行抓包，发现并没有异常

    POST / HTTP/1.1
Host: 138.68.183.83:30305
Referer: http://138.68.183.83:30305/
Content-Type: application/x-www-form-urlencoded
Content-Length: 37
Cookie: PHPSESSID=nsqgk152dlh578ojnd4hh0rfb4
Upgrade-Insecure-Requests: 1
   
hash=4a6ca4570c451b080cec591d374b55a1

  6. 可能在服务器侧使用Cookie存储了上一次字符串生成时间与本次提交时间进行了时间差计算

  7. 尝试使用Python脚本进行MD5

    • 代码

       import requests
 from lxml import etree
 import hashlib
      
 if __name__ == '__main__':
     url = 'http://138.68.183.83:30305/'
     session = requests.session()
     resp = session.get(url)
     source_str = etree.HTML(resp.text).xpath("/html/body/h3")[0].text
     md5_str = hashlib.md5(source_str.encode(encoding='UTF-8')).hexdigest()
     data = {'hash': md5_str}
     print(data)
     resp = session.post(url, data=data)
     print(resp.cookies, resp.content)

    • 响应

      <html>
 <head></head>
 <body style="background-color:powderblue;">
  <title>emdee five for life</title>
  <h1 align="center">MD5 encrypt this string</h1>
  <h3 align="center">4jqN3uwchnozTU1DH51U</h3>
  <p align="center">HTB{N1c3_ScrIpt1nG_B0i!}</p>
  <center>
   <form action="" method="post">
    <input type="text" name="hash" placeholder="MD5" align="\'center\'" />
    <br />
    <input type="submit" value="Submit" />
   </form>
  </center>
 </body>
</html>

  8. 因此，结果为HTB{N1c3_ScrIpt1nG_B0i!}

独立思考

本题较简单

产生过的疑问

本题较简单