【JS 逆向百例】网洛者反爬练习平台第七题：JSVMPZL 初体验

关注微信公众号：K哥爬虫，持续分享爬虫进阶、JS/安卓逆向等技术干货！

声明

本文章中所有内容仅供学习交流，抓包内容、敏感网址、数据接口均已做脱敏处理，严禁用于商业用途和非法用途，否则由此产生的一切后果均与作者无关，若有侵权，请在公众号联系我立即删除！

逆向目标

目标：网洛者反反爬虫练习平台第七题：JSVMPZL 初体验
链接：http://spider.wangluozhe.com/...
简介：平台注册需要邀请码，站长在群里，可后台回复交流群加群获取，或者直接加网站底部站长QQ获取。要求采集100页的全部数字，并计算所有数据加和。主要难点在于 vvv 大佬开发的 JS 混淆框架：jsvmpzl

逆向过程

直接搜索，或者跟栈，可以轻松找到加密入口，打开 F12 有两个反调试，一是无限 debugger，右键 Never pause here 即可，二是定时器，控制台输入 for (let i = 1; i < 99999; i++) window.clearInterval(i); 过掉即可。

跟进 y__()，就可以看到 jsvmpzl 混淆的代码了，如果有做过猿人学平台的题，会发现此混淆和猿人学第 18 题（https://match.yuanrenxue.com/...）是一样的，在 y__() 第一行下个断点，观察 __v_() 第一个参数 _，_[2][0] 你会发现有关 MD5 算法的一些特征，如下图所示：

那么我们直接大胆猜测一下，是不是就是某个数据经过 MD5 之后就是 _signature 了呢？再继续调试一下，注意 arguments 的变化：

很明显这个 window.byted_acrawler(window.sign()) 应该就是生成 _signature 的语句，这个方法和某字节系的 _signature 生成的方法名称是一样的，直接在控制台输出一下可以拿到值，其中 window.sign() 是取的时间戳：

我们前面猜测是 MD5，直接验证一下，发现并不是的，即便是同一个时间戳，经过 window.byted_acrawler() 后得到的值每次也都不一样：

Hook 关键方法

经过前面的分析，既然标准的 MD5 不行，那有没有可能是魔改的 MD5 呢？首先找个 JavaScript 标准的 MD5 代码看一下，比如：http://pajhome.org.uk/crypt/m...

可以注意到，源码里面有很多 md5_ff、md5_gg、md5_hh、md5_ii 的方法，最后一个值都是固定的，那么有没有可能此题就是在标准 MD5 的基础上修改了一些默认值呢？所以我们可以直接 Hook 这些关键方法，在控制台输出传入的值，来一一对比一下，看看默认值是否是一样的，为了方便观察，我们还可以为输出语句加上颜色，Hook 代码如下：

let oldFF = _[2][0]['md5_ff'];
let oldGG = _[2][0]['md5_gg'];
let oldHH = _[2][0]['md5_hh'];
let oldII = _[2][0]['md5_ii'];

let color_white_red = "color: white; background: red;"
let color_white_grey = "color: white; background: grey;"
let color_white_darkcyan = "color: white; background: darkcyan;"
let color_white_green = "color: white; background: green;"
let color_white_orange = "color: white; background: orange;"

_[2][0]['md5_ff'] = function (a, b, c, d, e, f, g) {
    debugger;
    let result = oldFF(a, b, c, d, e, f, g);
    console.log("%c Function: %c md5_ff %c Result: %c %s %c Params: %c %s, %s, %s, %s, %s, %s, %s ", color_white_red, color_white_grey, color_white_red, color_white_grey, result, color_white_red, color_white_grey, a, b, c, d, e, f, g)
    return result;
};

_[2][0]['md5_gg'] = function (a, b, c, d, e, f, g) {
    debugger;
    let result = oldGG(a, b, c, d, e, f, g);
    console.log("%c Function: %c md5_gg %c Result: %c %s %c Params: %c %s, %s, %s, %s, %s, %s, %s ", color_white_red, color_white_darkcyan, color_white_red, color_white_darkcyan, result, color_white_red, color_white_darkcyan, a, b, c, d, e, f, g)
    return result;
};

_[2][0]['md5_hh'] = function (a, b, c, d, e, f, g) {
    debugger;
    let result = oldHH(a, b, c, d, e, f, g);
    console.log("%c Function: %c md5_hh %c Result: %c %s %c Params: %c %s, %s, %s, %s, %s, %s, %s ", color_white_red, color_white_green, color_white_red, color_white_green, result, color_white_red, color_white_green, a, b, c, d, e, f, g)
    return result;
};

_[2][0]['md5_ii'] = function (a, b, c, d, e, f, g) {
    debugger;
    let result = oldII(a, b, c, d, e, f, g);
    console.log("%c Function: %c md5_ii %c Result: %c %s %c Params: %c %s, %s, %s, %s, %s, %s, %s ", color_white_red, color_white_orange, color_white_red, color_white_orange, result, color_white_red, color_white_orange, a, b, c, d, e, f, g)
    return result;
};

Hook 代码写得比较死板，熟悉 JS 的大佬可自己优化一下，注意注入代码的时机，清除定时器后，断点运行到 y__() 方法后再注入，然后取消断点，一直下一步，就可以在控制台看到输出的参数了，如下图所示：

与默认参数进行对比，可以发现 md5_hh() 里有两个默认参数被修改了：

默认的 -722521979 改成了 -722521939、76029189 改成了 76029185，本地代码修改一下即可：

/* ==================================
# @Time    : 2021-12-23
# @Author  : 微信公众号：K哥爬虫
# @FileName: challenge_7.js
# @Software: PyCharm
# ================================== */


/*
 * A JavaScript implementation of the RSA Data Security, Inc. MD5 Message
 * Digest Algorithm, as defined in RFC 1321.
 * Version 2.2 Copyright (C) Paul Johnston 1999 - 2009
 * Other contributors: Greg Holt, Andrew Kepert, Ydnar, Lostinet
 * Distributed under the BSD License
 * See http://pajhome.org.uk/crypt/md5 for more info.
 */

/*
 * Configurable variables. You may need to tweak these to be compatible with
 * the server-side, but the defaults work in most cases.
 */
var hexcase = 0;   /* hex output format. 0 - lowercase; 1 - uppercase        */
var b64pad  = "";  /* base-64 pad character. "=" for strict RFC compliance   */

/*
 * These are the functions you'll usually want to call
 * They take string arguments and return either hex or base-64 encoded strings
 */
function hex_md5(s)    { return rstr2hex(rstr_md5(str2rstr_utf8(s))); }
function b64_md5(s)    { return rstr2b64(rstr_md5(str2rstr_utf8(s))); }
function any_md5(s, e) { return rstr2any(rstr_md5(str2rstr_utf8(s)), e); }
function hex_hmac_md5(k, d)
  { return rstr2hex(rstr_hmac_md5(str2rstr_utf8(k), str2rstr_utf8(d))); }
function b64_hmac_md5(k, d)
  { return rstr2b64(rstr_hmac_md5(str2rstr_utf8(k), str2rstr_utf8(d))); }
function any_hmac_md5(k, d, e)
  { return rstr2any(rstr_hmac_md5(str2rstr_utf8(k), str2rstr_utf8(d)), e); }

/*
 * Perform a simple self-test to see if the VM is working
 */
function md5_vm_test()
{
  return hex_md5("abc").toLowerCase() == "900150983cd24fb0d6963f7d28e17f72";
}

/*
 * Calculate the MD5 of a raw string
 */
function rstr_md5(s)
{
  return binl2rstr(binl_md5(rstr2binl(s), s.length * 8));
}

/*
 * Calculate the HMAC-MD5, of a key and some data (raw strings)
 */
function rstr_hmac_md5(key, data)
{
  var bkey = rstr2binl(key);
  if(bkey.length > 16) bkey = binl_md5(bkey, key.length * 8);

  var ipad = Array(16), opad = Array(16);
  for(var i = 0; i < 16; i++)
  {
    ipad[i] = bkey[i] ^ 0x36363636;
    opad[i] = bkey[i] ^ 0x5C5C5C5C;
  }

  var hash = binl_md5(ipad.concat(rstr2binl(data)), 512 + data.length * 8);
  return binl2rstr(binl_md5(opad.concat(hash), 512 + 128));
}

/*
 * Convert a raw string to a hex string
 */
function rstr2hex(input)
{
  try { hexcase } catch(e) { hexcase=0; }
  var hex_tab = hexcase ? "0123456789ABCDEF" : "0123456789abcdef";
  var output = "";
  var x;
  for(var i = 0; i < input.length; i++)
  {
    x = input.charCodeAt(i);
    output += hex_tab.charAt((x >>> 4) & 0x0F)
           +  hex_tab.charAt( x        & 0x0F);
  }
  return output;
}

/*
 * Convert a raw string to a base-64 string
 */
function rstr2b64(input)
{
  try { b64pad } catch(e) { b64pad=''; }
  var tab = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
  var output = "";
  var len = input.length;
  for(var i = 0; i < len; i += 3)
  {
    var triplet = (input.charCodeAt(i) << 16)
                | (i + 1 < len ? input.charCodeAt(i+1) << 8 : 0)
                | (i + 2 < len ? input.charCodeAt(i+2)      : 0);
    for(var j = 0; j < 4; j++)
    {
      if(i * 8 + j * 6 > input.length * 8) output += b64pad;
      else output += tab.charAt((triplet >>> 6*(3-j)) & 0x3F);
    }
  }
  return output;
}

/*
 * Convert a raw string to an arbitrary string encoding
 */
function rstr2any(input, encoding)
{
  var divisor = encoding.length;
  var i, j, q, x, quotient;

  /* Convert to an array of 16-bit big-endian values, forming the dividend */
  var dividend = Array(Math.ceil(input.length / 2));
  for(i = 0; i < dividend.length; i++)
  {
    dividend[i] = (input.charCodeAt(i * 2) << 8) | input.charCodeAt(i * 2 + 1);
  }

  /*
   * Repeatedly perform a long division. The binary array forms the dividend,
   * the length of the encoding is the divisor. Once computed, the quotient
   * forms the dividend for the next step. All remainders are stored for later
   * use.
   */
  var full_length = Math.ceil(input.length * 8 /
                                    (Math.log(encoding.length) / Math.log(2)));
  var remainders = Array(full_length);
  for(j = 0; j < full_length; j++)
  {
    quotient = Array();
    x = 0;
    for(i = 0; i < dividend.length; i++)
    {
      x = (x << 16) + dividend[i];
      q = Math.floor(x / divisor);
      x -= q * divisor;
      if(quotient.length > 0 || q > 0)
        quotient[quotient.length] = q;
    }
    remainders[j] = x;
    dividend = quotient;
  }

  /* Convert the remainders to the output string */
  var output = "";
  for(i = remainders.length - 1; i >= 0; i--)
    output += encoding.charAt(remainders[i]);

  return output;
}

/*
 * Encode a string as utf-8.
 * For efficiency, this assumes the input is valid utf-16.
 */
function str2rstr_utf8(input)
{
  var output = "";
  var i = -1;
  var x, y;

  while(++i < input.length)
  {
    /* Decode utf-16 surrogate pairs */
    x = input.charCodeAt(i);
    y = i + 1 < input.length ? input.charCodeAt(i + 1) : 0;
    if(0xD800 <= x && x <= 0xDBFF && 0xDC00 <= y && y <= 0xDFFF)
    {
      x = 0x10000 + ((x & 0x03FF) << 10) + (y & 0x03FF);
      i++;
    }

    /* Encode output as utf-8 */
    if(x <= 0x7F)
      output += String.fromCharCode(x);
    else if(x <= 0x7FF)
      output += String.fromCharCode(0xC0 | ((x >>> 6 ) & 0x1F),
                                    0x80 | ( x         & 0x3F));
    else if(x <= 0xFFFF)
      output += String.fromCharCode(0xE0 | ((x >>> 12) & 0x0F),
                                    0x80 | ((x >>> 6 ) & 0x3F),
                                    0x80 | ( x         & 0x3F));
    else if(x <= 0x1FFFFF)
      output += String.fromCharCode(0xF0 | ((x >>> 18) & 0x07),
                                    0x80 | ((x >>> 12) & 0x3F),
                                    0x80 | ((x >>> 6 ) & 0x3F),
                                    0x80 | ( x         & 0x3F));
  }
  return output;
}

/*
 * Encode a string as utf-16
 */
function str2rstr_utf16le(input)
{
  var output = "";
  for(var i = 0; i < input.length; i++)
    output += String.fromCharCode( input.charCodeAt(i)        & 0xFF,
                                  (input.charCodeAt(i) >>> 8) & 0xFF);
  return output;
}

function str2rstr_utf16be(input)
{
  var output = "";
  for(var i = 0; i < input.length; i++)
    output += String.fromCharCode((input.charCodeAt(i) >>> 8) & 0xFF,
                                   input.charCodeAt(i)        & 0xFF);
  return output;
}

/*
 * Convert a raw string to an array of little-endian words
 * Characters >255 have their high-byte silently ignored.
 */
function rstr2binl(input)
{
  var output = Array(input.length >> 2);
  for(var i = 0; i < output.length; i++)
    output[i] = 0;
  for(var i = 0; i < input.length * 8; i += 8)
    output[i>>5] |= (input.charCodeAt(i / 8) & 0xFF) << (i%32);
  return output;
}

/*
 * Convert an array of little-endian words to a string
 */
function binl2rstr(input)
{
  var output = "";
  for(var i = 0; i < input.length * 32; i += 8)
    output += String.fromCharCode((input[i>>5] >>> (i % 32)) & 0xFF);
  return output;
}

/*
 * Calculate the MD5 of an array of little-endian words, and a bit length.
 */
function binl_md5(x, len)
{
  /* append padding */
  x[len >> 5] |= 0x80 << ((len) % 32);
  x[(((len + 64) >>> 9) << 4) + 14] = len;

  var a =  1732584193;
  var b = -271733879;
  var c = -1732584194;
  var d =  271733878;

  for(var i = 0; i < x.length; i += 16)
  {
    var olda = a;
    var oldb = b;
    var oldc = c;
    var oldd = d;

    a = md5_ff(a, b, c, d, x[i+ 0], 7 , -680876936);
    d = md5_ff(d, a, b, c, x[i+ 1], 12, -389564586);
    c = md5_ff(c, d, a, b, x[i+ 2], 17,  606105819);
    b = md5_ff(b, c, d, a, x[i+ 3], 22, -1044525330);
    a = md5_ff(a, b, c, d, x[i+ 4], 7 , -176418897);
    d = md5_ff(d, a, b, c, x[i+ 5], 12,  1200080426);
    c = md5_ff(c, d, a, b, x[i+ 6], 17, -1473231341);
    b = md5_ff(b, c, d, a, x[i+ 7], 22, -45705983);
    a = md5_ff(a, b, c, d, x[i+ 8], 7 ,  1770035416);
    d = md5_ff(d, a, b, c, x[i+ 9], 12, -1958414417);
    c = md5_ff(c, d, a, b, x[i+10], 17, -42063);
    b = md5_ff(b, c, d, a, x[i+11], 22, -1990404162);
    a = md5_ff(a, b, c, d, x[i+12], 7 ,  1804603682);
    d = md5_ff(d, a, b, c, x[i+13], 12, -40341101);
    c = md5_ff(c, d, a, b, x[i+14], 17, -1502002290);
    b = md5_ff(b, c, d, a, x[i+15], 22,  1236535329);

    a = md5_gg(a, b, c, d, x[i+ 1], 5 , -165796510);
    d = md5_gg(d, a, b, c, x[i+ 6], 9 , -1069501632);
    c = md5_gg(c, d, a, b, x[i+11], 14,  643717713);
    b = md5_gg(b, c, d, a, x[i+ 0], 20, -373897302);
    a = md5_gg(a, b, c, d, x[i+ 5], 5 , -701558691);
    d = md5_gg(d, a, b, c, x[i+10], 9 ,  38016083);
    c = md5_gg(c, d, a, b, x[i+15], 14, -660478335);
    b = md5_gg(b, c, d, a, x[i+ 4], 20, -405537848);
    a = md5_gg(a, b, c, d, x[i+ 9], 5 ,  568446438);
    d = md5_gg(d, a, b, c, x[i+14], 9 , -1019803690);
    c = md5_gg(c, d, a, b, x[i+ 3], 14, -187363961);
    b = md5_gg(b, c, d, a, x[i+ 8], 20,  1163531501);
    a = md5_gg(a, b, c, d, x[i+13], 5 , -1444681467);
    d = md5_gg(d, a, b, c, x[i+ 2], 9 , -51403784);
    c = md5_gg(c, d, a, b, x[i+ 7], 14,  1735328473);
    b = md5_gg(b, c, d, a, x[i+12], 20, -1926607734);

    a = md5_hh(a, b, c, d, x[i+ 5], 4 , -378558);
    d = md5_hh(d, a, b, c, x[i+ 8], 11, -2022574463);
    c = md5_hh(c, d, a, b, x[i+11], 16,  1839030562);
    b = md5_hh(b, c, d, a, x[i+14], 23, -35309556);
    a = md5_hh(a, b, c, d, x[i+ 1], 4 , -1530992060);
    d = md5_hh(d, a, b, c, x[i+ 4], 11,  1272893353);
    c = md5_hh(c, d, a, b, x[i+ 7], 16, -155497632);
    b = md5_hh(b, c, d, a, x[i+10], 23, -1094730640);
    a = md5_hh(a, b, c, d, x[i+13], 4 ,  681279174);
    d = md5_hh(d, a, b, c, x[i+ 0], 11, -358537222);
    // 注释掉的是默认值
    // c = md5_hh(c, d, a, b, x[i+ 3], 16, -722521979);
    c = md5_hh(c, d, a, b, x[i+ 3], 16, -722521939);
    // b = md5_hh(b, c, d, a, x[i+ 6], 23,  76029189);
    b = md5_hh(b, c, d, a, x[i+ 6], 23,  76029185);
    a = md5_hh(a, b, c, d, x[i+ 9], 4 , -640364487);
    d = md5_hh(d, a, b, c, x[i+12], 11, -421815835);
    c = md5_hh(c, d, a, b, x[i+15], 16,  530742520);
    b = md5_hh(b, c, d, a, x[i+ 2], 23, -995338651);

    a = md5_ii(a, b, c, d, x[i+ 0], 6 , -198630844);
    d = md5_ii(d, a, b, c, x[i+ 7], 10,  1126891415);
    c = md5_ii(c, d, a, b, x[i+14], 15, -1416354905);
    b = md5_ii(b, c, d, a, x[i+ 5], 21, -57434055);
    a = md5_ii(a, b, c, d, x[i+12], 6 ,  1700485571);
    d = md5_ii(d, a, b, c, x[i+ 3], 10, -1894986606);
    c = md5_ii(c, d, a, b, x[i+10], 15, -1051523);
    b = md5_ii(b, c, d, a, x[i+ 1], 21, -2054922799);
    a = md5_ii(a, b, c, d, x[i+ 8], 6 ,  1873313359);
    d = md5_ii(d, a, b, c, x[i+15], 10, -30611744);
    c = md5_ii(c, d, a, b, x[i+ 6], 15, -1560198380);
    b = md5_ii(b, c, d, a, x[i+13], 21,  1309151649);
    a = md5_ii(a, b, c, d, x[i+ 4], 6 , -145523070);
    d = md5_ii(d, a, b, c, x[i+11], 10, -1120210379);
    c = md5_ii(c, d, a, b, x[i+ 2], 15,  718787259);
    b = md5_ii(b, c, d, a, x[i+ 9], 21, -343485551);

    a = safe_add(a, olda);
    b = safe_add(b, oldb);
    c = safe_add(c, oldc);
    d = safe_add(d, oldd);
  }
  return Array(a, b, c, d);
}

/*
 * These functions implement the four basic operations the algorithm uses.
 */
function md5_cmn(q, a, b, x, s, t)
{
  return safe_add(bit_rol(safe_add(safe_add(a, q), safe_add(x, t)), s),b);
}
function md5_ff(a, b, c, d, x, s, t)
{
  return md5_cmn((b & c) | ((~b) & d), a, b, x, s, t);
}
function md5_gg(a, b, c, d, x, s, t)
{
  return md5_cmn((b & d) | (c & (~d)), a, b, x, s, t);
}
function md5_hh(a, b, c, d, x, s, t)
{
  return md5_cmn(b ^ c ^ d, a, b, x, s, t);
}
function md5_ii(a, b, c, d, x, s, t)
{
  return md5_cmn(c ^ (b | (~d)), a, b, x, s, t);
}

/*
 * Add integers, wrapping at 2^32. This uses 16-bit operations internally
 * to work around bugs in some JS interpreters.
 */
function safe_add(x, y)
{
  var lsw = (x & 0xFFFF) + (y & 0xFFFF);
  var msw = (x >> 16) + (y >> 16) + (lsw >> 16);
  return (msw << 16) | (lsw & 0xFFFF);
}

/*
 * Bitwise rotate a 32-bit number to the left.
 */
function bit_rol(num, cnt)
{
  return (num << cnt) | (num >>> (32 - cnt));
}

function getSignature() {
    return hex_md5(Date.parse(Date()).toString())
}

console.log(getSignature())

Python 调用代码：

# ==================================
# --*-- coding: utf-8 --*--
# @Time    : 2021-12-23
# @Author  : 微信公众号：K哥爬虫
# @FileName: challenge_7.py
# @Software: PyCharm
# ==================================


import time
import execjs
import requests


challenge_api = "http://spider.wangluozhe.com/challenge/api/7"
headers = {
    "Cookie": "Cookie 替换成你的",
    "Host": "spider.wangluozhe.com",
    "Origin": "http://spider.wangluozhe.com",
    "Referer": "http://spider.wangluozhe.com/challenge/7",
    "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.45 Safari/537.36",
    "X-Requested-With": "XMLHttpRequest"
}


def get_signature():
    now = str(int(time.time())) + "000"
    with open('challenge_7.js', 'r', encoding='utf-8') as f:
        wlz_js = execjs.compile(f.read())
    # signature = wlz_js.call("getSignature")
    signature = wlz_js.call("hex_md5", now)
    print("signature: ", signature)
    return signature


def main():
    result = 0
    for page in range(1, 101):
        data = {
            "page": page,
            "count": 10,
            "_signature": get_signature()
        }
        response = requests.post(url=challenge_api, headers=headers, data=data).json()
        print(response)
        for d in response["data"]:
            result += d["value"]
    print("结果为: ", result)


if __name__ == '__main__':
    main()

这里还有一点小细节，如果是 Python 生成时间戳传入 JS 的 hex_md5 方法的话，要保证时间戳的最后三位为0，不然校验通不过，通常的写法是 str(int(time.time() * 1000))，这里要改一下：str(int(time.time())) + "000"，不用 Python 的话，也可以在 JS 里写个方法直接返回 hex_md5(Date.parse(Date()).toString()) 也行。

还有一个问题就是如果你找的 MD5 代码不规范，准确来说是和题目使用的 MD5 代码不太一样的话，有可能本地要改的地方就不止这两处了，所以尽量找一个方法名都一样的JS，能省不少事儿。

日志断点 / 插桩调试

除了 Hook 以外，我们还可以通过插桩调试的方式，将整个生成 _signature 的流程、涉及到的参数、生成的值，都通过日志的形式打印出来，逆向分析其逻辑。PS：插桩，即日志断点，鼠标右键选择 Add logpoint 即可添加一个日志断点，相当于 console.log()，此功能是 Chrome 73 版本新增的。

Add breakpoint：添加普通断点；
Add conditional breakpoint：添加条件断点，满足条件才断下；
Add logpoint：添加日志断点；
Never pause here：永不在此处断下；
Add script to ignore list：网站的部分 JS，比如 jquery.min.js 之类的库文件，我们单步调试的时候并不想进入到该文件中，那么可以将此类文件右键添加忽略掉。

关键的日志断点有以下三处：