超星考试pos参数破译

李恒道

FBI WARNING
这里的超星考试指本人的原创单机游戏【超级星星V.666】单词大考验关卡
并非通俗意义超星
请勿联想
感谢

感谢@涛之雨 大佬在我失业之后为我积极推荐工作，经过大佬的内推成功进入了美团送外卖
正文
点击考试预览可以追到AST部分这里可以看到是ob混淆+字符串转义

我们先解决字符串转义部分
直接利用babel的最小化就可以将字符串转义压缩成正常字符串

[JavaScript] 纯文本查看 复制代码

const parser = require("@babel/parser");
const generator = require("@babel/generator").default;
const code_js = fs.readFileSync("./chaoxing_exam.js", {
  encoding: "utf-8",
});
const ast = parser.parse(code_js)
let code = generator(ast, {
  minified: true,
  jsescOption: { minimal: true },
}).code;
fs.writeFile("./convert1.js", code, (err) => {});

然后查看一下结果

然后解字符串，这里是_0x56bc
直接抬手一个转义，因为没有多层，所以只处理_0x56bc即可
老规矩，复制_0x56bc到nodejs作为解密函数
首先测试一下，发现卡死了，多半是正则爆破，搜索Reg找了

[JavaScript] 纯文本查看 复制代码

      _0x4337b4["prototype"]["RvZSqA"] = function () {
        var _0x403f16 = new RegExp(this["MTxJBI"] + this["FMdsHI"]);
        var _0x55e9af = _0x403f16["test"](this["ZxBleI"]["toString"]())
          ? --this["pNCgln"][1]
          : --this["pNCgln"][0];
        return this["AfmIcA"](_0x55e9af);
      };
      _0x4337b4["prototype"]["AfmIcA"] = function (_0x172353) {
        if (!Boolean(~_0x172353)) {
          return _0x172353;
        }
        return this["ebdBfN"](this["GRlANK"]);
      };
      _0x4337b4["prototype"]["ebdBfN"] = function (_0xa7fe72) {
        for (
          var _0x5f3bbf = 0, _0x1ed88a = this["pNCgln"]["length"];
          _0x5f3bbf < _0x1ed88a;
          _0x5f3bbf++
        ) {
          this["pNCgln"]["push"](Math["round"](Math["random"]()));
          _0x1ed88a = this["pNCgln"]["length"];
        }
        return _0xa7fe72(this["pNCgln"][0]);
      };

应该是正则下面的三元运算符在捣乱，我们跑一下发现是false，所以直接强制改成true内的--this["pNCgln"][1]

[JavaScript] 纯文本查看 复制代码

     _0x4337b4["prototype"]["RvZSqA"] = function () {
        var _0x403f16 = new RegExp(this["MTxJBI"] + this["FMdsHI"]);
        var _0x55e9af = --this["pNCgln"][1]
        return this["AfmIcA"](_0x55e9af);
      };

在运行发现还是存在内存爆破
向上找到了字符串混淆内存在分支污染和内存爆破

直接将第一个设为false，第二个设为true
再运行crp函数

解密成功
然后直接开始解字符串混淆

[JavaScript] 纯文本查看 复制代码

const fuck_js = fs.readFileSync("./convert2.js", {
  encoding: "utf-8",
});
const ast = parser.parse(fuck_js);
traverse(ast, {
  CallExpression(path) {
    if (path.node.callee.name === "_0x56bc") {
      let loc1 = path.node.arguments[0].value;
      let loc2 = path.node.arguments[1]?.value;
      let str_node = types.stringLiteral(_0x56bc(loc1, loc2));
      path.replaceInline(str_node);
    }
  },
});
let code = generator(ast, {
  minified: true,
  jsescOption: { minimal: true },
}).code;
fs.writeFile("./convert3.js", code, (err) => {});

已经具备基本的可读了

接下来就是硬干了
我们目标比较简单

分析这些数据吧
value像是鼠标的数据，我们先看value,确实是鼠标的相对页面键值

[JavaScript] 纯文本查看 复制代码

    var scrollLeft =
        document["documentElement"]["scrollLeft"] ||
        document["body"]["scrollLeft"],
      scrollTop =
        document["documentElement"]["scrollTop"] ||
        document["body"]["scrollTop"];
    (mouseMap["x"] =
      winEvent["pageX"] || winEvent["clientX"] + scrollLeft),
      (mouseMap["y"] =
        winEvent["pageY"] || winEvent["clientY"] + scrollTop),
    var value =
      "(" +
      Math["ceil"](mouseMap["x"]) +
      "|" +
      Math["ceil"](mouseMap["y"]) +
      ")";

接下来看qid，取自页面的questionId数据

[JavaScript] 纯文本查看 复制代码

 _0x210627 = document["getElementById"]("questionId"),
(qid = _0x210627["value"])

看rd，随机数

[JavaScript] 纯文本查看 复制代码

var rd = Math["random"](),

接下来只剩enc和_edt了，先看enc
里面是一个闭包
看大概应该是一个转义字符代码，懒得搞了，直接抽离

[JavaScript] 纯文本查看 复制代码

function getEncData(posData, userId, questionId, randomNum, rd) {
  let userIdAndQuestionIdAndRandom =
    userId + "_" + questionId + "|" + randomNum;
  if (
    null == userIdAndQuestionIdAndRandom ||
    userIdAndQuestionIdAndRandom["length"] <= 0
  )
    return null;
  for (
    var _0x469e62 = "", _0x388a1f = 0;
    _0x388a1f < userIdAndQuestionIdAndRandom["length"];
    _0x388a1f++
  )
    _0x469e62 +=
      userIdAndQuestionIdAndRandom["charCodeAt"](_0x388a1f)["toString"]();
  var _0x210627 = Math["floor"](_0x469e62["length"] / 5),
    _0x215858 = parseInt(
      _0x469e62["charAt"](_0x210627) +
        _0x469e62["charAt"](2 * _0x210627) +
        _0x469e62["charAt"](3 * _0x210627) +
        _0x469e62["charAt"](4 * _0x210627)
    ),
    _0x408603 = Math["ceil"](userIdAndQuestionIdAndRandom["length"] / 2),
    _0x3ed445 = Math["pow"](2, 31) - 1;
  if (_0x215858 < 2) return null;
  var rd = rd,
    _0x58d995 = Math["round"](1000000000 * rd) % 100000000;
  10 < (_0x469e62 += _0x58d995)["length"] &&
    (_0x469e62 = parseInt(_0x469e62["substring"](0, 10))["toString"]()),
    (_0x469e62 = (_0x215858 * _0x469e62 + _0x408603) % _0x3ed445);
  var _0x3c1f52 = "",
    _0x435dce = "";
  for (_0x388a1f = 0; _0x388a1f < posData["length"]; _0x388a1f++)
    (_0x435dce +=
      (_0x3c1f52 = parseInt(
        posData["charCodeAt"](_0x388a1f) ^
          Math["floor"]((_0x469e62 / _0x3ed445) * 255)
      )) < 16
        ? "0" + _0x3c1f52["toString"](16)
        : _0x3c1f52["toString"](16)),
      (_0x469e62 = (_0x215858 * _0x469e62 + _0x408603) % _0x3ed445);
  for (_0x58d995 = _0x58d995["toString"](16); _0x58d995["length"] < 8; )
    _0x58d995 = "0" + _0x58d995;
  return (_0x435dce += _0x58d995);
}
console.log(
  'getEncData("(1890|22)", userId, questionId, 265, 0.7836752714778081)',
  getEncData("(1890|22)", 用户id, 试卷id, 265, 0.7836752714778081)
);

官方数据

抽离代码

代码生成成功，然后看最后的_edt，来源是      "&_edt=" +
(_0x408603 + randomNumA)，其中randomNumA是一个生成的随机数

[JavaScript] 纯文本查看 复制代码

  function _0xe7b063() {
    if ("ySLJF" !== "ySLJF") {
      (function () {
        return ![];
      })
        ["constructor"]("debu" + "gger")
        ["apply"]("stateObject");
    } else {
      return Math["floor"](10 * Math["random"]());
    }
  }

而另外一个603的变量则是时间

[JavaScript] 纯文本查看 复制代码

_0x408603 = "" + new Date()["getTime"](),

至此全部破译完毕
结语
撒花

FCGkitty

看到混淆加密头就疼，头皮发麻

LuckyClover

参数破译，进来学习一下