【JS逆向系列】某乎x96参数与jsvmp初体验
【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
直接在全局中搜索
发现只有两处地方引用到，那么直接打上断点刷新
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
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
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
这个就是我们需要的结果，跟进去看看
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。
在客户端中，通过特定的解释器，不断执行一条一条的指令
既然是jsvmp，那么肯定会有vmp的一些特征
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
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
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
这里的【e】就是那个很长的字符串，调用的【this.D】方法
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】
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
【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
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
继续单步第一条的操作码
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】，
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
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。
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 = "AxjgB5MAnACoAJwBpAAAABAAIAKcAqgAMAq0AzRJZAZwUpwCqACQACACGAKcBKAAIAOcBagAIAQYAjAUGgKcBqFAuAc5hTSHZAZwqrAIGgA0QJEAJAAYAzAUGgOcCaFANRQ0R2QGcOKwChoANECRACQAsAuQABgDnAmgAJwMgAGcDYwFEAAzBmAGcSqwDhoANECRACQAGAKcD6AAGgKcEKFANEcYApwRoAAxB2AGcXKwEhoANECRACQAGAKcE6AAGgKcFKFANEdkBnGqsBUaADRAkQAkABgCnBagAGAGcdKwFxoANECRACQAGAKcGKAAYAZx+rAZGgA0QJEAJAAYA5waoABgBnIisBsaADRAkQAkABgCnBygABoCnB2hQDRHZAZyWrAeGgA0QJEAJAAYBJwfoAAwFGAGcoawIBoANECRACQAGAOQALAJkAAYBJwfgAlsBnK+sCEaADRAkQAkABgDkACwGpAAGAScH4AJbAZy9rAiGgA0QJEAJACwI5AAGAScH6AAkACcJKgAnCWgAJwmoACcJ4AFnA2MBRAAMw5gBnNasCgaADRAkQAkABgBEio0R5EAJAGwKSAFGACcKqAAEgM0RCQGGAYSATRFZAZzshgAtCs0QCQAGAYSAjRFZAZz1hgAtCw0QCQAEAAgB7AtIAgYAJwqoAASATRBJAkYCRIANEZkBnYqEAgaBxQBOYAoBxQEOYQ0giQKGAmQABgAnC6ABRgBGgo0UhD/MQ8zECALEAgaBxQBOYAoBxQEOYQ0gpEAJAoYARoKNFIQ/zEPkAAgChgLGgkUATmBkgAaAJwuhAUaCjdQFAg5kTSTJAsQCBoHFAE5gCgHFAQ5hDSCkQAkChgBGgo0UhD/MQ+QACAKGAsaCRQCOYGSABoAnC6EBRoKN1AUEDmRNJMkCxgFGgsUPzmPkgAaCJwvhAU0wCQFGAUaCxQGOZISPzZPkQAaCJwvhAU0wCQFGAUaCxQMOZISPzZPkQAaCJwvhAU0wCQFGAUaCxQSOZISPzZPkQAaCJwvhAU0wCQFGAkSAzRBJAlz/B4FUAAAAwUYIAAIBSITFQkTERwABi0GHxITAAAJLwMSGRsXHxMZAAk0Fw8HFh4NAwUABhU1EBceDwAENBcUEAAGNBkTGRcBAAFKAAkvHg4PKz4aEwIAAUsACDIVHB0QEQ4YAAsuAzs7AAoPKToKDgAHMx8SGQUvMQABSAALORoVGCQgERcCAxoACAU3ABEXAgMaAAsFGDcAERcCAxoUCgABSQAGOA8LGBsPAAYYLwsYGw8AAU4ABD8QHAUAAU8ABSkbCQ4BAAFMAAktCh8eDgMHCw8AAU0ADT4TGjQsGQMaFA0FHhkAFz4TGjQsGQMaFA0FHhk1NBkCHgUbGBEPAAFCABg9GgkjIAEmOgUHDQ8eFSU5DggJAwEcAwUAAUMAAUAAAUEADQEtFw0FBwtdWxQTGSAACBwrAxUPBR4ZAAkqGgUDAwMVEQ0ACC4DJD8eAx8RAAQ5GhUYAAFGAAAABjYRExELBAACWhgAAVoAQAg/PTw0NxcQPCQ5C3JZEBs9fkcnDRcUAXZia0Q4EhQgXHojMBY3MWVCNT0uDhMXcGQ7AUFPHigkQUwQFkhaAkEACjkTEQspNBMZPC0ABjkTEQsrLQ==";
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 = "AxjgB5MAnACoAJwBpAAAABAAIAKcAqgAMAq0AzRJZAZwUpwCqACQACACGAKcBKAAIAOcBagAIAQYAjAUGgKcBqFAuAc5hTSHZAZwqrAIGgA0QJEAJAAYAzAUGgOcCaFANRQ0R2QGcOKwChoANECRACQAsAuQABgDnAmgAJwMgAGcDYwFEAAzBmAGcSqwDhoANECRACQAGAKcD6AAGgKcEKFANEcYApwRoAAxB2AGcXKwEhoANECRACQAGAKcE6AAGgKcFKFANEdkBnGqsBUaADRAkQAkABgCnBagAGAGcdKwFxoANECRACQAGAKcGKAAYAZx+rAZGgA0QJEAJAAYA5waoABgBnIisBsaADRAkQAkABgCnBygABoCnB2hQDRHZAZyWrAeGgA0QJEAJAAYBJwfoAAwFGAGcoawIBoANECRACQAGAOQALAJkAAYBJwfgAlsBnK+sCEaADRAkQAkABgDkACwGpAAGAScH4AJbAZy9rAiGgA0QJEAJACwI5AAGAScH6AAkACcJKgAnCWgAJwmoACcJ4AFnA2MBRAAMw5gBnNasCgaADRAkQAkABgBEio0R5EAJAGwKSAFGACcKqAAEgM0RCQGGAYSATRFZAZzshgAtCs0QCQAGAYSAjRFZAZz1hgAtCw0QCQAEAAgB7AtIAgYAJwqoAASATRBJAkYCRIANEZkBnYqEAgaBxQBOYAoBxQEOYQ0giQKGAmQABgAnC6ABRgBGgo0UhD/MQ8zECALEAgaBxQBOYAoBxQEOYQ0gpEAJAoYARoKNFIQ/zEPkAAgChgLGgkUATmBkgAaAJwuhAUaCjdQFAg5kTSTJAsQCBoHFAE5gCgHFAQ5hDSCkQAkChgBGgo0UhD/MQ+QACAKGAsaCRQCOYGSABoAnC6EBRoKN1AUEDmRNJMkCxgFGgsUPzmPkgAaCJwvhAU0wCQFGAUaCxQGOZISPzZPkQAaCJwvhAU0wCQFGAUaCxQMOZISPzZPkQAaCJwvhAU0wCQFGAUaCxQSOZISPzZPkQAaCJwvhAU0wCQFGAkSAzRBJAlz/B4FUAAAAwUYIAAIBSITFQkTERwABi0GHxITAAAJLwMSGRsXHxMZAAk0Fw8HFh4NAwUABhU1EBceDwAENBcUEAAGNBkTGRcBAAFKAAkvHg4PKz4aEwIAAUsACDIVHB0QEQ4YAAsuAzs7AAoPKToKDgAHMx8SGQUvMQABSAALORoVGCQgERcCAxoACAU3ABEXAgMaAAsFGDcAERcCAxoUCgABSQAGOA8LGBsPAAYYLwsYGw8AAU4ABD8QHAUAAU8ABSkbCQ4BAAFMAAktCh8eDgMHCw8AAU0ADT4TGjQsGQMaFA0FHhkAFz4TGjQsGQMaFA0FHhk1NBkCHgUbGBEPAAFCABg9GgkjIAEmOgUHDQ8eFSU5DggJAwEcAwUAAUMAAUAAAUEADQEtFw0FBwtdWxQTGSAACBwrAxUPBR4ZAAkqGgUDAwMVEQ0ACC4DJD8eAx8RAAQ5GhUYAAFGAAAABjYRExELBAACWhgAAVoAQAg/PTw0NxcQPCQ5C3JZEBs9fkcnDRcUAXZia0Q4EhQgXHojMBY3MWVCNT0uDhMXcGQ7AUFPHigkQUwQFkhaAkEACjkTEQspNBMZPC0ABjkTEQsrLQ==";
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。
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
当第二次断下时，进行单步调试
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
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] ^ 42
b64_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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