Using vlx-vmengine for deobfuscation
vlx-vmengine-jvmis a Java bytecode execution engine implemented in Java. Please refer to it for usage.https://github.com/vlinx-io/vlx-vmengine-jvm
There is the following simple paragraphJavaCode
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();
}
}
After being compiled into class files and obfuscated using a certain obfuscation engine, the following files are obtained,
After opening with jadx, it was found that, except formainOutside of the function, everything else is unrecognizable, and the string has been encrypted.
However, even if it is obfuscated, the basic structure of the class and the byte code information still exist, using ClassViewer Opena.classYou can see the class methods and bytecode information
No matter how to confuse, it can only obfuscate the code at the static level and increase the complexity of analysis. The original runtime logic of the program still needs to be restored in dynamic execution. Use vlx-vmengine-jvm to run obfuscated code. main Method, obtaining the following output
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='<init>', 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"
From the console output, you can see that the program restores the original behavior, which is print output.Hi, George, and at the same time, we can also judge from the output that the decryption function of the string isprivate static java.lang.String a.a(int,int)，its parameters are7144and-13249If you continue to use vmengine for debugginga.a(int,int)By using this method, you can identify the string encryption method used by this obfuscation engine.