python|【JS逆向系列】某乎x96参数与jsvmp初体验 javascript|python|算法|javascript

【JS逆向系列】某乎x96参数与jsvmp初体验

- js分析
- jsvmp分析
- 第一种解决方案-补环境
- 第二种解决方案-修改操作码
- 第三种解决方案-算法还原
- 参考文章

样品网址：aHR0cHM6Ly93d3cuemhpaHUuY29tLw==
js分析在搜索的时候，请求头中会存在一个x-zse-96的参数，这个参数是加密的，本篇文章主要分析这个参数是如何生成的

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直接在全局中搜索

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发现只有两处地方引用到，那么直接打上断点刷新

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此时发现参数已经生成，前面的【2.0_】是固定值，后面的【y】是前面的【O.signature】
继续往前看【O】，这是由一个自执行函数生成的，在里面也下一个断点

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这里有三个参数，第一个【e】是请求的地址，第二个【t】是请求体，第三个【n】是一个对象，里面又有三个值，其中【zse93】是另一个请求头的值，是一个定值，【dc0】是cookie中的【d_c0】的值，还有一个【xZst81】是空的，可以不用管
接着的参数【s】就是过滤掉布尔值为false的值然后进行拼接，所以实际【s】就是【{x_zse_93}+{path}+{d_c0}】
然后我们需要的参数【signature】就是【s】经过两个函数生成的，那么首先来看看【f】函数

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看到返回值是一个长度32的字符串，猜测这个函数很有可能是一个md5的计算，从在线网站计算一下对比，发现这个就是一个标准的md5算法
接着就是【u】函数

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这个就是我们需要的结果，跟进去看看

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接着在单步调试的时候，发现会在各个函数之间反复横跳。看到这个前面有一个很长的字符串【AxjgB5MAnACoAJwBpAAAABAAIAKcAqgAM*****************】，这种很有可能就是jsvmp。
jsvmp分析 jsvmp就是将js源代码首先编译为字节码，得到的这种字节码就变成只有操作码（opcode）和操作数（Operands），这是其中一个前端代码的保护技术。
整体架构流程是服务器端通过对JavaScript代码词法分析 -> 语法分析 -> 语法树->生成AST->生成私有指令->生成对应私有解释器，将私有指令加密与私有解释器发送给浏览器，就开始一边解释，一边执行。

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在客户端中，通过特定的解释器，不断执行一条一条的指令

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既然是jsvmp，那么肯定会有vmp的一些特征

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这里的【G】就是vm初始化，这里有几个参数需要特别注意

参数	映射意义
this.r	全局变量
this.C	pc寄存器
this.k	本地变量
this.f	调用堆栈
this.J	操作指令

上面的仅仅是我个人的理解，不一定对
第一种解决方案-补环境首先把整段代码扣到本地，在开头处加上jsdom的代码

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const{JSDOM}=require("jsdom"); const dom=new JSDOM("Hello world "); window=dom.window;

然后尝试生成的参数是否与网页一致

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测试发现是一模一样的，那么扣代码的方法就完成了
第二种解决方案-修改操作码那么有没有办法不用补环境呢？那也是有的，那么接着来进一步分析这个jsvmp，调试一下上面补环境得到的js

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这里的【e】就是那个很长的字符串，调用的【this.D】方法

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这里是解码这个字符串，得到一段数值数组，赋值给【this.G】和一段字符串数组，赋值给【this.b】

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解码完了以后，有一个【this.R】，这个如果两条运行两条指令之间的时间，如果大于500毫秒，就认为是在调试，被强制退出了，所以在调试的时候可以把这个if判断注释掉

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【this.C】是pc寄存器，从【this.G】不断取出操作码，然后使用【this.e】方法执行这条操作码，跟进去第一条操作码

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因为之前解码那个长字符串的时候，是两个字节得出一个操作码，可以看出一个操作码是一个short类型，这里【61440】的二进制是【11110000 00000000】，并且左移12位，就是取最高的4位。2的4次方是16，刚好对应着16种不同的操作指令

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继续单步第一条的操作码

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这里计算了一个【this.h】的值，多调试几个会发现，除了计算【this.t】是真正的操作类型下面的操作码，其他都是操作数。所以这里得到一个【this.h】的操作数是【7】，

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计算完真正的操作码和操作数后，调用了对应的【e】方法来执行

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这是一个函数初始化，因为之前说过把【r】当作全局变量。所以这里把内部的【r】函数，绑定到全局的第四个值，那么，第一条指令就执行完成了，接着回到循环，执行第二条，第三条指令，一次类推，直到所有的指令的执行完。
那么这里的代码具有一定的共性，那么能不能自己根据这些操作码，来还原出伪代码呢，来试一下。
【python|【JS逆向系列】某乎x96参数与jsvmp初体验】首先把解码的函数复制过来，并生成四个全局变量

const parser = require("@babel/parser"); // 为parser提供模板引擎 const template = require("@babel/template").default; // 遍历AST const traverse = require("@babel/traverse").default; // 操作节点，比如判断节点类型，生成新的节点等 const types = require("@babel/types"); // 将语法树转换为源代码 const generator = require("@babel/generator"); // 操作文件 const fs = require("fs"); var k = function (e) { for (var t = 66, n = [], r = 0; r < e.length; r++) { var i = 24 ^ e.charCodeAt(r) ^ t; n.push(String.fromCharCode(i)); t = i; }return n.join(""); }; let vmp_bin = "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"; let opcode = []; for (let t = atob(vmp_bin), n = t.charCodeAt(0) << 8 | t.charCodeAt(1), i = 2; i < n + 2; i += 2) { opcode.push(t.charCodeAt(i) << 8 | t.charCodeAt(i + 1)); } opcode.push(0); let opstr = []; for (let t = atob(vmp_bin), n = t.charCodeAt(0) << 8 | t.charCodeAt(1), a = n + 2; a < t.length; ) { var c = t.charCodeAt(a) << 8 | t.charCodeAt(a + 1), u = t.slice(a + 2, a + 2 + c); opstr.push(k(u)); a += c + 2; }let ast = parser.parse(""); ast.program.body.push(types.variableDeclaration("var", [ types.variableDeclarator(types.identifier('global_0')), types.variableDeclarator(types.identifier('global_1')), types.variableDeclarator(types.identifier('global_2')), types.variableDeclarator(types.identifier('global_3')) ]));

接着后面就是一个大的switch，针对每条指令，生成一个js代码，例如第一条的操作类型是14

case 14: let into_code = 4095 & opcode[pc]; ast.program.body.push(types.functionDeclaration(types.identifier('_0x' + into_code), [], types.blockStatement([]))); blockstatement.push(types.expressionStatement(types.assignmentExpression("=", types.identifier('global_3'), types.identifier('_0x' + into_code)))); pc++; break;

这是一个函数初始化指令，需要生成一个函数，并且赋值给全局变量，如此类推，把所有的指令都还原出来，相当于自己实现了一个解释器

const parser = require("@babel/parser"); // 为parser提供模板引擎 const template = require("@babel/template").default; // 遍历AST const traverse = require("@babel/traverse").default; // 操作节点，比如判断节点类型，生成新的节点等 const types = require("@babel/types"); // 将语法树转换为源代码 const generator = require("@babel/generator"); // 操作文件 const fs = require("fs"); var k = function (e) { for (var t = 66, n = [], r = 0; r < e.length; r++) { var i = 24 ^ e.charCodeAt(r) ^ t; n.push(String.fromCharCode(i)); t = i; }return n.join(""); }; let vmp_bin = "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"; let opcode = []; for (let t = atob(vmp_bin), n = t.charCodeAt(0) << 8 | t.charCodeAt(1), i = 2; i < n + 2; i += 2) { opcode.push(t.charCodeAt(i) << 8 | t.charCodeAt(i + 1)); } opcode.push(0); let opstr = []; for (let t = atob(vmp_bin), n = t.charCodeAt(0) << 8 | t.charCodeAt(1), a = n + 2; a < t.length; ) { var c = t.charCodeAt(a) << 8 | t.charCodeAt(a + 1), u = t.slice(a + 2, a + 2 + c); opstr.push(k(u)); a += c + 2; }let ast = parser.parse(""); ast.program.body.push(types.variableDeclaration("var", [ types.variableDeclarator(types.identifier('global_0')), types.variableDeclarator(types.identifier('global_1')), types.variableDeclarator(types.identifier('global_2')), types.variableDeclarator(types.identifier('global_3')) ])); function get_blockstatement(pc, Local, blockstatement){ let Stack = []; while (opcode[pc] !== 0){ let t, s, i, h, a, c, n; switch ((61440 & opcode[pc]) >> 12) { case 0: break; case 1: break; case 2: break; case 3: break; case 4: break; case 5: break; case 6: break; case 7: break; case 8: break; case 9: t = (4095 & opcode[pc]) >> 10; s = (1023 & opcode[pc]) >> 8; i = 1023 & opcode[pc]; h = 63 & opcode[pc]; switch (t) { case 0: Stack.push(types.identifier('global_' + s)); pc++; break; case 1: break; case 2: break; case 3: Stack.push(types.stringLiteral(opstr[h])); pc++; break } break; case 10: t = (4095 & opcode[pc]) >> 10; a = (1023 & opcode[pc]) >> 8; c = (255 & opcode[pc]) >> 6; switch (t) { case 0: break; case 1: s = Stack.pop(), i = Stack.pop(); blockstatement.push( types.expressionStatement( types.assignmentExpression( "=", types.memberExpression( types.identifier('global_' + c), s, true ), i ) ) ); pc++; break; case 2: h = Stack.pop(); blockstatement.push(types.expressionStatement(types.assignmentExpression("=", types.identifier('global_' + a), types.callExpression(types.identifier('eval'), [h])))); pc++; break; } break; case 11: break; case 12: break; case 13: break; case 14: let into_code = 4095 & opcode[pc]; ast.program.body.push(types.functionDeclaration(types.identifier('_0x' + into_code), [], types.blockStatement([]))); blockstatement.push(types.expressionStatement(types.assignmentExpression("=", types.identifier('global_3'), types.identifier('_0x' + into_code)))); pc++; break; case 15: break; } } return blockstatement }ast.program.body.push(types.expressionStatement(types.callExpression(types.functionExpression(null, [], types.blockStatement(get_blockstatement(0, [], []))), []))); let code = generator.default(ast).code; console.log(code);

运行后可以得到初始化部分的伪代码

var global_0, global_1, global_2, global_3; function _0x7() {}(function () { global_3 = _0x7; global_0 = eval("__g"); global_0["_encrypt"] = global_3; })();

从伪代码中可以看出，确实是把基址是【0x7】的函数，动态绑定到【__g】对象的【_encrypt】属性下面，上面我们生成签名的时候，确实也是调用的这个
继续完善解释器的代码，可以得到下面的伪代码

var global_0, global_1, global_2, global_3; function _0x7(params_0) { var local_0 = params_0; global_0 = 0; var local_2 = global_0; global_0 = eval("window"); global_0 = t(global_0); global_1 = "undefined"; global_1 = global_0 !== global_1; if (global_1) { global_0 = eval("window"); local_2 = global_0; }global_0 = local_2; global_0 = global_0["navigator"]; var local_3 = global_0; global_0 = eval("Object"); var local_4 = global_0; global_0 = local_2; global_0 = !global_0; global_1 = local_2; global_1 = global_1["name"]; global_2 = "nodejs"; global_2 = global_1 == global_2; global_1 = global_0 || global_2; if (global_1) { global_0 = "\x10"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_3; global_0 = !global_0; global_1 = local_3; global_1 = global_1["userAgent"]; global_1 = !global_1; global_1 = global_0 || global_1; if (global_1) { global_0 = "\x11"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = "headless"; global_0 = local_3; global_0 = global_0["userAgent"]; global_3 = global_0["toLowerCase"](); global_3 = global_3["indexOf"](global_0); global_0 = 0; global_0 = global_3 >= global_0; if (global_0) { global_0 = "\x12"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_2; global_0 = global_0["callPhantom"]; global_1 = local_2; global_1 = global_1["_phantom"]; global_1 = global_0 || global_1; global_0 = local_2; global_0 = global_0["__phantomas"]; global_0 = global_1 || global_0; if (global_0) { global_0 = "\x13"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_2; global_0 = global_0["buffer"]; global_1 = local_2; global_1 = global_1["Buffer"]; global_1 = global_0 || global_1; if (global_1) { global_0 = "\x14"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_2; global_0 = global_0["emit"]; if (global_0) { global_0 = "\x15"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_2; global_0 = global_0["spawn"]; if (global_0) { global_0 = "\x16"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_3; global_0 = global_0["webdriver"]; if (global_0) { global_0 = "\x17"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_2; global_0 = global_0["domAutomation"]; global_1 = local_2; global_1 = global_1["domAutomationController"]; global_1 = global_0 || global_1; if (global_1) { global_0 = "\x18"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_4; global_0 = global_0["getOwnPropertyDescriptor"]; global_0 = !global_0; if (global_0) { global_0 = "\x19"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_3; global_0 = "userAgent"; global_0 = local_4; global_3 = global_0["getOwnPropertyDescriptor"](global_0, global_0); if (global_3) { global_0 = "\x1A"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_3; global_0 = "webdriver"; global_0 = local_4; global_3 = global_0["getOwnPropertyDescriptor"](global_0, global_0); if (global_3) { global_0 = "\x1B"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = "[native code]"; global_0 = local_4; global_0 = global_0["getOwnPropertyDescriptor"]; global_0 = eval("Function"); global_0 = global_0["prototype"]; global_0 = global_0["toString"]; global_3 = global_0["call"](global_0); global_3 = global_3["indexOf"](global_0); global_0 = 0; global_0 = global_3 < global_0; if (global_0) { global_0 = "\x1C"; global_1 = local_0; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_1; global_1 = 42; global_1 = global_0 || global_1; var local_1 = global_1; global_0 = ""; var local_5 = global_0; global_0 = local_0; global_0 = global_0["length"]; global_1 = 3; global_1 = global_0 % global_1; var local_6 = global_1; global_0 = local_6; global_1 = 1; global_1 = global_0 == global_1; if (global_1) { global_0 = local_0; global_1 = "\0\0"; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_6; global_1 = 2; global_1 = global_0 == global_1; if (global_1) { global_0 = local_0; global_1 = "\0"; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = 0; var local_7 = global_0; global_0 = "RuPtXwxpThIZ0qyz_9fYLCOV8B1mMGKs7UnFHgN3iDaWAJE-Qrk2ecSo6bjd4vl5"; var local_8 = global_0; global_0 = local_0; global_0 = global_0["length"]; global_1 = 1; global_1 = global_0 - global_1; var local_9 = global_1; global_0 = local_9; global_1 = 0; global_1 = global_0 >= global_1; for (; global_1; ) { global_0 = 8; global_1 = local_7; global_2 = 1; global_2 = global_1 + global_2; local_7 = global_2; global_2 = 4; global_2 = global_1 % global_2; global_1 = global_0 * global_2; var local_10 = global_1; global_0 = local_9; global_0 = local_0; global_3 = global_0["charCodeAt"](global_0); global_0 = local_1; global_1 = local_10; global_1 = global_0 >>> global_1; global_0 = 255; global_0 = global_1 & global_0; global_0 = global_3 ^ global_0; var local_11 = global_0; global_0 = 8; global_1 = local_7; global_2 = 1; global_2 = global_1 + global_2; local_7 = global_2; global_2 = 4; global_2 = global_1 % global_2; global_1 = global_0 * global_2; local_10 = global_1; global_0 = local_1; global_1 = local_10; global_1 = global_0 >>> global_1; global_0 = 255; global_0 = global_1 & global_0; local_10 = global_0; global_0 = local_11; global_1 = local_9; global_2 = 1; global_2 = global_1 - global_2; global_1 = local_0; global_3 = global_1["charCodeAt"](global_2); global_1 = local_10; global_1 = global_3 ^ global_1; global_2 = 8; global_2 = global_1 << global_2; global_1 = global_0 | global_2; local_11 = global_1; global_0 = 8; global_1 = local_7; global_2 = 1; global_2 = global_1 + global_2; local_7 = global_2; global_2 = 4; global_2 = global_1 % global_2; global_1 = global_0 * global_2; local_10 = global_1; global_0 = local_1; global_1 = local_10; global_1 = global_0 >>> global_1; global_0 = 255; global_0 = global_1 & global_0; local_10 = global_0; global_0 = local_11; global_1 = local_9; global_2 = 2; global_2 = global_1 - global_2; global_1 = local_0; global_3 = global_1["charCodeAt"](global_2); global_1 = local_10; global_1 = global_3 ^ global_1; global_2 = 16; global_2 = global_1 << global_2; global_1 = global_0 | global_2; local_11 = global_1; global_0 = local_5; global_1 = local_11; global_2 = 63; global_2 = global_1 & global_2; global_1 = local_8; global_3 = global_1["charAt"](global_2); global_1 = global_0 + global_3; local_5 = global_1; global_0 = local_5; global_1 = local_11; global_2 = 6; global_2 = global_1 >>> global_2; global_1 = 63; global_1 = global_2 & global_1; global_1 = local_8; global_3 = global_1["charAt"](global_1); global_1 = global_0 + global_3; local_5 = global_1; global_0 = local_5; global_1 = local_11; global_2 = 12; global_2 = global_1 >>> global_2; global_1 = 63; global_1 = global_2 & global_1; global_1 = local_8; global_3 = global_1["charAt"](global_1); global_1 = global_0 + global_3; local_5 = global_1; global_0 = local_5; global_1 = local_11; global_2 = 18; global_2 = global_1 >>> global_2; global_1 = 63; global_1 = global_2 & global_1; global_1 = local_8; global_3 = global_1["charAt"](global_1); global_1 = global_0 + global_3; local_5 = global_1; global_0 = local_9; global_1 = 3; global_1 = global_0 - global_1; local_9 = global_1; global_0 = local_9; global_1 = 0; global_1 = global_0 >= global_1; }global_3 = local_5; return global_3; }(function () { global_3 = _0x7; global_0 = eval("__g"); global_0["_encrypt"] = global_3; })();

伪代码是没有办法直接运行的，需要继续优化，才可能可以运行起来。但是在这里也可以看到比较直观的逻辑了。所以能不能运行关系并不大
可以看出，前面一半左右，都是在检测环境，如果检测不通过，就会添加一个字节，导致最后的结果不一样。例如，如果你是使用自动化工具来爬取的，那么很有可能【webdriver】这个属性就为真，那么参数就会被添加一个【\x17】，服务端解码结果发现有一个【\x17】，就知道是自动化工具，而不是正常的浏览器，那么就不返回数据了。
这时就有一个想法了，如果是js代码，那么我可以直接把环境检测的代码注释掉，那么就直接不需要环境也可以得出正确的结果，那么在jsvmp中，能不能有类似的操作呢？那么就要巧妙的使用到pc寄存器了。

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上图这里是最后一个环境检测，离这里最近的字符串是【indexOf】，那么在解密字符串的地方下一个断点

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当第二次断下时，进行单步调试

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当来到下一个跳转指令的时候，pc寄存器的指向是从209到214，也就是说214的地方才是结算签名的开始，前面的都是环境检测，那么知道真正开始的地方，我们就可以修改pc寄存器的值了，当pc寄存器的值为7的时候，也就是函数的入口，把它直接改成214

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添加完这个后，就删除前面添加的jsdom，再次运行，发现结果也是正确的。绝了，这居然真的可以，到这里第二种方法就完成了
第三种解决方案-算法还原根据前面我们已经知道，只有后半部分的伪代码才是真实的逻辑，那么我们就只看后半部分来还原就好了

global_0 = local_1; global_1 = 42; global_1 = global_0 || global_1; var local_1 = global_1; global_0 = ""; var local_5 = global_0; global_0 = local_0; global_0 = global_0["length"]; global_1 = 3; global_1 = global_0 % global_1; var local_6 = global_1; global_0 = local_6; global_1 = 1; global_1 = global_0 == global_1; if (global_1) { global_0 = local_0; global_1 = "\0\0"; global_1 = global_0 + global_1; local_0 = global_1; }global_0 = local_6; global_1 = 2; global_1 = global_0 == global_1; if (global_1) { global_0 = local_0; global_1 = "\0"; global_1 = global_0 + global_1; local_0 = global_1; }

这里大致可以看出是对参数进行填充成3的倍数

global_0 = 0; var local_7 = global_0; global_0 = "RuPtXwxpThIZ0qyz_9fYLCOV8B1mMGKs7UnFHgN3iDaWAJE-Qrk2ecSo6bjd4vl5"; var local_8 = global_0; global_0 = local_0; global_0 = global_0["length"]; global_1 = 1; global_1 = global_0 - global_1; var local_9 = global_1; global_0 = local_9; global_1 = 0; global_1 = global_0 >= global_1;

然后初始化了一个长度64的字符串，根据前后可以猜测很有可能是一个base64的编码算法，只不过不是一个标准的base64，而是修改了编码表以及一些算法细节
继续往后看，是一个循环，这里就是编码的开始

global_0 = 8; global_1 = local_7; global_2 = 1; global_2 = global_1 + global_2; local_7 = global_2; global_2 = 4; global_2 = global_1 % global_2; global_1 = global_0 * global_2; var local_10 = global_1; global_0 = local_9; global_0 = local_0; global_3 = global_0["charCodeAt"](global_0);

这里是从字符串后后面开始取值，正常的base64编码都是从前面开始的，但是这里是从后面开始的，这是一个魔改点，base64编码是三个字节一个单位，所以python还原的话就要从后面开始三个字节一组反转

for i in range(len(in_put) - 1, 0, -3): b64_in += in_put[i - 2: i + 1]

接着继续看后面的操作

global_0 = local_1; global_1 = local_10; global_1 = global_0 >>> global_1; global_0 = 255; global_0 = global_1 & global_0; global_0 = global_3 ^ global_0; var local_11 = global_0; global_0 = 8; global_1 = local_7; global_2 = 1; global_2 = global_1 + global_2; local_7 = global_2; global_2 = 4; global_2 = global_1 % global_2; global_1 = global_0 * global_2; local_10 = global_1; global_0 = local_1; global_1 = local_10; global_1 = global_0 >>> global_1; global_0 = 255; global_0 = global_1 & global_0; local_10 = global_0; global_0 = local_11; global_1 = local_9; global_2 = 1; global_2 = global_1 - global_2; global_1 = local_0;

这里的实际逻辑经过优化后，就是12个字节为一组。然后2，4，6的位置与42进行异或，这里是第二个魔改点

for i inrange(0, len(b64_in), 12): b64_in[i + 2], b64_in[i + 4], b64_in[i + 6] = b64_in[i + 2] ^ 42, b64_in[i + 4] ^ 42, b64_in[i + 6] ^ 42

接着就是base64编码，但是编码的端序不相同，所以每一组的端序都要修改，这是第三个魔改点，完整的python代码如下

def x96_b64encode(in_put: str) -> str: in_put = in_put.encode('utf-8') while len(in_put) % 3 != 0: in_put += bytes([0])table1 = list('RuPtXwxpThIZ0qyz_9fYLCOV8B1mMGKs7UnFHgN3iDaWAJE-Qrk2ecSo6bjd4vl5') table2 = list('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/') table3 = {table2[v]: table1[v] for v in range(len(table1))}b64_in = bytearray() for i in range(len(in_put) - 1, 0, -3): b64_in += in_put[i - 2: i + 1] for i in range(0, len(b64_in), 12): b64_in[i + 2], b64_in[i + 4], b64_in[i + 6] = b64_in[i + 2] ^ 42, b64_in[i + 4] ^ 42, b64_in[i + 6] ^ 42b64_out = ''.join(list(map(lambda n: table3[n], list(base64.b64encode(b64_in).decode())))) return ''.join([b64_out[i: i + 4][::-1] for i in range(0, len(b64_out), 4)])

测试这个函数，与浏览器生成的值是一样的，所以到这里，第三种方法也解决了。到此为止，对jsvmp也有了初步的了解。
参考文章 1.H5应用加固防破解-JS虚拟机保护方案
2.某网站视频加密的wasm略谈（二）
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