What kind of obfuscation is this

Question

I saw some Java applications that have code like this:

public class Test {
  public Test();
    Code:
       0: aload_0       
       1: invokespecial #1                  // Method     java/lang/Object."":()V
   4: return        

  public static void main(java.lang.String[]);
    Code:
       0: invokestatic  #2                  // Method     printOne:()V
       3: invokestatic  #2                  // Method     printOne:()V
       6: invokestatic  #3                  // Method     printTwo:()V
       9: return        

  public static void printOne();
    Code:
       0: getstatic     #4                  // Field     java/lang/System.out:Ljava/io/PrintStream;
       3: ldc           #5                  // String Hello World
       5: invokevirtual #6                  // Method     java/io/PrintStream.println:(Ljava/lang/String;)V
       8: return        

  public static void printTwo();
    Code:
       0: invokestatic  #2                  // Method     printOne:()V
       3: invokestatic  #2                  // Method     printOne:()V
       6: return        
}

And I wanted to know which kind of obfuscation is this, and what are the tools that can obfuscate a JAR file like that.

That's JVM byte code assembler. You can use `javac` to generate it. — daniu, Sep 26 '18 at 12:53
He means javap. Javac turns source code into byte code. Javap deassembles it. — GhostCat, Sep 26 '18 at 12:56
Most IDEs have a decompiler as a plugin. In use fernflower which will turn the byte code back into java code. — Peter Lawrey, Sep 26 '18 at 13:38

score 4 · Accepted Answer · answered Sep 26 '18 at 12:55

4

Run javap -c on a compiled java class and you will get java byte code. That's not obfuscation, rather de-compilation. A pretty good resource from IBM is Java bytecode:Understanding bytecode makes you a better programmer

answered Sep 26 '18 at 12:55

Mike

1,924
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16

score 1 · Answer 2 · answered Sep 26 '18 at 13:07

that is what javac generated - the compiler for the java code. It's actually really easy to transpose that to code:

public class Test {
   // an implicit constructor:
   public Test(){

   }

   public static void testOne(){
      System.out.println("Hello World");
   }

   public static String testTwo(){
      testOne();
      testOne();
   }

}

What kind of obfuscation is this

2 Answers2