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This article focuses on "how to implement the Java confusion compiler", interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Next let the editor to take you to learn "Java confusion compiler how to implement" it!

Q: what is obfuscator?

A: because the Java program is dynamically linked when it is running, the compiled object file contains symbol tables, which makes the Java program easily decompiled. The obfuscator can disrupt the symbol information in the class file, which makes reverse engineering very difficult.

Q: what's wrong with the existing obfuscators?

A: all the existing obfuscators confuse the compiled class files, which requires two steps: compilation and obfuscation. Not all symbols need to be confused. If you are developing a class library, or if some classes need to be loaded dynamically, those public API must leave the symbols unchanged so that others can use your library. The existing obfuscator provides a GUI or script way to configure the symbolic names that need to be preserved. If the program is large, the configuration becomes very complex, and once the program modifies the configuration, it has to be redone. Some obfuscators can adjust the order of bytecode to make decompilation more difficult, but I have experienced errors in the execution of programs after confusion.

Q: how does the Java obfuscation compiler work?

A: Java obfuscation compiler is completed on the basis of the Java compiler (javac) provided by Sun JDK. It modifies the code generation process, confuses the intermediate code generated by the compiler, and finally generates the class file, so that compilation and obfuscation can be completed in only one step. In addition, symbol retention instructions can be inserted into the source program to control which symbols need to be retained, without the need for separate configuration.

Q: how do I install and run JOC?

A: download joc.jar and run java-jar joc.jar to start the Java obfuscation compiler. The command line argument of joc is exactly the same as javac, but a new parameter-Xobfuscate has been added. Its usage is as follows:

-Xobfuscate:

It specifies the level of confusion, which can be the following:

-Xobfuscate:none does not confuse

-Xobfuscate:private confuses elements of all private access levels

-Xobfuscate:package confuses all private or package private elements

-Xobfuscate:protected confuses all private, package private, protected elements

-Xobfuscate:public confuses all the elements

-Xobfuscate:all is equivalent to-Xobfuscate:public.

If you use-Xobfuscate without a level parameter, it is equivalent to-Xobfuscate:package

Q: how do I use symbol retention instructions?

A: in addition to controlling the level of symbol obfuscation with the-Xobfuscate parameter on the command line, you can also use the symbol retention instruction in the source code to control which symbols need to be retained. The symbol retention instruction is an Java documentation comment instruction that can be inserted into the documentation comments of classes and class members, for example:

/ * *

* This class should preserve.

* @ preserve

, /

Public class Foo {

/ * *

* You can specify which field should be preserved.

* @ preserve

, /

Private int x

/ * *

* This field is not preserved.

, /

Private int y

/ * *

* You can also preserve methods.

* @ preserve

, /

Public void hello () {}

/ * *

* This method is not preserved.

, /

Private void collect () {}

}

If there is no @ preserve directive, it is determined whether the symbol is retained based on the level of confusion and the access level of the member.

The symbol retention instruction for a class can be accompanied by a retention level parameter to control the symbol retention of class members, including:

@ preserve reserves only the class name, and the retention of class members is determined by the-Xobfuscate command line argument

@ preserve public retains all public members

@ preserve protected retains all public and protected members

@ preserve package retains all public, protected, package private members

@ preserve private retains all members

@ preserve all is equivalent to @ preserve private

Q: what are the limitations of JOC?

A: separate compilation is not supported. All source files must be compiled confusedly.

Source file:

Import java.awt.event.*

Import javax.swing.*

Public class AboutBox extends JDialog

{

Public AboutBox ()

{

InitForm ()

}

JPanel panel1 = new JPanel ()

JButton button1 = new JButton ()

JLabel jLabel2 = new JLabel ()

JTextArea jTextArea1 = new JTextArea ()

/ * *

* NOTE: The following code is required by the form designer.

* It can be modified using the form editor. Do not

* modify it using the code editor.

, /

Private void initForm ()

{

This.setDefaultCloseOperation (WindowConstants.DISPOSE_ON_CLOSE)

This.getContentPane () .setLayout (new java.awt.CardLayout ()

This.setModal (true)

This.setResizable (false)

This.setTitle ("About...")

Panel1.setLayout (null)

Button1.setText ("OK")

Button1.setBounds (272,168,88,24)

Panel1.add (button1)

JLabel2.setText ("File System Viewer for Swing 1.1.1")

JLabel2.setVerticalAlignment (SwingConstants.TOP)

JLabel2.setBounds (64,32,240,56)

Panel1.add (jLabel2)

JTextArea1.setFont (new java.awt.Font ("Dialog", 0,10))

JTextArea1.setLineWrap (true)

JTextArea1.setOpaque (false)

JTextArea1.setText ("This computer program is protected by copyright law.")

JTextArea1.setWrapStyleWord (true)

JTextArea1.setBounds (8,112,256,80)

Panel1.add (jTextArea1)

This.getContentPane () .add (panel1, Card1)

This.setSize (376,228)

Button1.addActionListener (new java.awt.event.ActionListener () {

Public void actionPerformed (java.awt.event.ActionEvent ev) {

Button1_actionPerformed (ev)

})

}

Private void button1_actionPerformed (ActionEvent ev)

{

This.dispose ()

}

}

The result of decompilation with JAD after Javac compilation:

Import java.awt.*

Import java.awt.event.ActionEvent

Import java.awt.event.ActionListener

Import javax.swing.*

Import javax.swing.text.JTextComponent

Public class AboutBox extends JDialog

{

JPanel panel1

JButton button1

JLabel jLabel2

JTextArea jTextArea1

Public AboutBox ()

{

Panel1 = new JPanel ()

Button1 = new JButton ()

JLabel2 = new JLabel ()

JTextArea1 = new JTextArea ()

InitForm ()

}

Private void initForm ()

{

SetDefaultCloseOperation (2)

GetContentPane () .setLayout (new CardLayout ()

SetModal (true)

SetResizable (false)

SetTitle ("About...")

Panel1.setLayout (null)

Button1.setText ("OK")

Button1.setBounds (272,168,88,24)

Panel1.add (button1)

JLabel2.setText ("File System Viewer for Swing 1.1.1")

JLabel2.setVerticalAlignment (1)

JLabel2.setBounds (64,32,240,56)

Panel1.add (jLabel2)

JTextArea1.setFont (new Font ("Dialog", 0,10))

JTextArea1.setLineWrap (true)

JTextArea1.setOpaque (false)

JTextArea1.setText ("This computer program is protected by copyright law.")

JTextArea1.setWrapStyleWord (true)

JTextArea1.setBounds (8,112,256,80)

Panel1.add (jTextArea1)

GetContentPane () .add (panel1, Card1)

SetSize (376,228)

Button1.addActionListener (new ActionListener () {

Public void actionPerformed (ActionEvent actionevent)

{

Button1_actionPerformed (actionevent)

}

});

}

Private void button1_actionPerformed (ActionEvent actionevent)

{

Dispose ()

}

}

The result of decompilation with JAD after obfuscation compilation by JOC:

Import java.awt.*

Import java.awt.event.ActionEvent

Import java.awt.event.ActionListener

Import javax.swing.*

Import javax.swing.text.JTextComponent

Public class AboutBox extends JDialog

{

JPanel _ $1

JButton _ $2

JLabel _ $3

JTextArea _ $4

Public AboutBox ()

{

_ $1 = new JPanel ()

_ $2 = new JButton ()

_ $3 = new JLabel ()

_ $4 = new JTextArea ()

_ $1 ()

}

Private void _ $1 ()

{

2

This

JVM INSTR swap

SetDefaultCloseOperation ()

GetContentPane () .setLayout (new CardLayout ()

True

This

JVM INSTR swap

SetModal ()

False

This

JVM INSTR swap

SetResizable ()

"About..."

This

JVM INSTR swap

SetTitle ()

_ $1.setLayout (null)

_ $2.setText ("OK")

_ $2

168

272

JVM INSTR swap

24

88

JVM INSTR swap

SetBounds ()

_ $1.add (_ $2)

_ $3.setText ("File System Viewer for Swing 1.1.1")

_ $3.setVerticalAlignment (1)

_ $3

32

64

JVM INSTR swap

56

240

JVM INSTR swap

SetBounds ()

_ $1.add (_ $3)

_ $4

JVM INSTR new # 13

JVM INSTR dup

0

"Dialog"

JVM INSTR swap

10

Font ()

SetFont ()

_ $4.setLineWrap (true)

_ $4.setOpaque (false)

_ $4.setText ("This computer program is protected by copyright law.")

_ $4.setWrapStyleWord (true)

_ $4

112

8

JVM INSTR swap

80

256

JVM INSTR swap

SetBounds ()

_ $1.add (_ $4)

GetContentPane () .add (_ $1, "Card1")

376

This

JVM INSTR swap

228

SetSize ()

_ $2.addActionListener (new IIlIlIIIIlllIIII (this))

Return

}

Private void _ $1 (ActionEvent actionevent)

{

Dispose ()

}

/ *

Static void access$0 (AboutBox aboutbox, ActionEvent actionevent)

{

Actionevent

Aboutbox

JVM INSTR swap

_ $1 ()

Return

}

, /

/ / Unreferenced inner classes:

/ * anonymous class * /

Final class IIlIlIIIIlllIIII

Implements ActionListener

{

Public void actionPerformed (ActionEvent actionevent)

{

AboutBox.access$0 (AboutBox.this, actionevent)

}

{

AboutBox.this

This

JVM INSTR swap

This$0

}

}

}

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