使用vlx-vmengine进行反混淆

vlx-vmengine-jvm是一个使用Java实现的Java字节码执行引擎，其使用请参考https://github.com/vlinx-io/vlx-vmengine-jvm

有如下一段简单的Java代码

class HelloWorld {

    private String name = "";

    public HelloWorld(String name){
        this.name = name;
    }

    public void sayHi(){
        System.out.println("Hi, " + name);
    }

    public static void main(String[] args){
        
        String name = "George";
        HelloWorld hello = new HelloWorld(name);

        hello.sayHi();

    }

}

编译为类文件，并使用某个混淆引擎混淆后，得到如下文件，

a.class

使用jadx打开后发现，除了main 函数之外，其他信息都面目全非，字符串也已经被加密。

但是即使混淆了，类的基本结构与字节码信息仍然是存在的，使用ClassViewer 打开a.class, 可以看到类的方法与字节码信息

无论如何做混淆，也仅能够在静态层面上混淆代码，提升分析的复杂度，在动态运行中仍然需要还原程序原来的运行逻辑，使用vlx-vmengine-jvm

运行混淆后代码的main方法，得到如下输出

2023-05-21 18:19:05 [DEBUG] LocalVars: [kotlin.Unit, kotlin.Unit, kotlin.Unit]
2023-05-21 18:19:05 [DEBUG] "L0: SIPUSH"
2023-05-21 18:19:05 [DEBUG] "push" 7144
2023-05-21 18:19:05 [DEBUG] "L3: SIPUSH"
2023-05-21 18:19:05 [DEBUG] "push" -13249
2023-05-21 18:19:05 [DEBUG] "L6: INVOKESTATIC"
2023-05-21 18:19:05 [DEBUG] "#20"
2023-05-21 18:19:05 [DEBUG] "class a, NameAndType(name='a', type='(II)Ljava/lang/String;')"
2023-05-21 18:19:05 [DEBUG] private static java.lang.String a.a(int,int)
2023-05-21 18:19:05 [DEBUG] "pop" -13249
2023-05-21 18:19:05 [DEBUG] "pop" 7144
2023-05-21 18:19:05 [DEBUG] 	Execute method: private static java.lang.String a.a(int,int)
2023-05-21 18:19:05 [DEBUG] 	Args: [7144, -13249]
2023-05-21 18:19:05 [DEBUG] "push" "George"
2023-05-21 18:19:05 [DEBUG] "L9: ASTORE_1"
2023-05-21 18:19:05 [DEBUG] "pop" "George"
2023-05-21 18:19:05 [DEBUG] "localVars[1] = George"
2023-05-21 18:19:05 [DEBUG] "L10: NEW"
2023-05-21 18:19:05 [DEBUG] class a
2023-05-21 18:19:05 [DEBUG] "push" InstanceToCreate(clazz=class a)
2023-05-21 18:19:05 [DEBUG] "L13: DUP"
2023-05-21 18:19:05 [DEBUG] "pop" InstanceToCreate(clazz=class a)
2023-05-21 18:19:05 [DEBUG] "push" InstanceToCreate(clazz=class a)
2023-05-21 18:19:05 [DEBUG] "push" InstanceToCreate(clazz=class a)
2023-05-21 18:19:05 [DEBUG] "L14: ALOAD_1"
2023-05-21 18:19:05 [DEBUG] "#1"
2023-05-21 18:19:05 [DEBUG] "push" "George"
2023-05-21 18:19:05 [DEBUG] "L15: INVOKESPECIAL"
2023-05-21 18:19:05 [DEBUG] "#47"
2023-05-21 18:19:05 [DEBUG] "class a, NameAndType(name='&lt;init&gt;', type='(Ljava/lang/String;)V')"
2023-05-21 18:19:05 [DEBUG] public a(java.lang.String)
2023-05-21 18:19:05 [DEBUG] "pop" "George"
2023-05-21 18:19:05 [DEBUG] "Execute new instance: public a(java.lang.String)"
2023-05-21 18:19:05 [DEBUG] "Args: [George]"
2023-05-21 18:19:05 [DEBUG] "pop" InstanceToCreate(clazz=class a)
2023-05-21 18:19:05 [DEBUG] "L18: ASTORE_2"
2023-05-21 18:19:05 [DEBUG] "pop" a@4612b856
2023-05-21 18:19:05 [DEBUG] "localVars[2] = a@4612b856"
2023-05-21 18:19:05 [DEBUG] "L19: ALOAD_2"
2023-05-21 18:19:05 [DEBUG] "#2"
2023-05-21 18:19:05 [DEBUG] "push" a@4612b856
2023-05-21 18:19:05 [DEBUG] "L20: INVOKEVIRTUAL"
2023-05-21 18:19:05 [DEBUG] "#54"
2023-05-21 18:19:05 [DEBUG] "class a, NameAndType(name='a', type='()V')"
2023-05-21 18:19:05 [DEBUG] public void a.a()
2023-05-21 18:19:05 [DEBUG] "pop" a@4612b856
2023-05-21 18:19:05 [DEBUG] 	Execute method: public void a.a()
2023-05-21 18:19:05 [DEBUG] 	Receiver: a@4612b856
2023-05-21 18:19:05 [DEBUG] 	Args: [a@4612b856]
Hi, George
2023-05-21 18:19:05 [DEBUG] "L23: RETURN"

从控制台输出可以看到程序还原了原来的行为，即打印输出Hi, George，同时从输出中我们也可以判断字符串的解密函数在private static java.lang.String a.a(int,int)，其参数为7144与-13249，如果继续使用vmengine调试a.a(int,int)方法即可发现该混淆引擎使用的字符串加密方法。

使用vlx-vmengine进行反混淆

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