-- Corsaire Security Advisory -- 
 
Title: ChainKey Java Code Protection Bypass issue 
Date: 06.11.06  
Application: Java Code Protection 
Environment: Java Virtual Machine 
Author: Stephen de Vries [stephen.de.vries@corsaire.com] 
Audience: General distribution 
Reference: c061106-001 
 
 
-- Scope -- 
 
The aim of this document is to clearly define an issue that exists with 
the ChainKey Java Code Protection product [1], that will allow an 
attacker to circumvent the encryption protection and de-compile any 
protected Java application. 
 

-- History -- 
 
Discovered: 6.11.06 (Stephen de Vries)
Vendor notified: 08.11.06 (responded 25.12.06) 
Document released: 12.01.07 
 
 
-- Overview -- 
 
The ChainKey Java Code Protection product is described as "...a tool to 
protect your program codes written in Java, through multi-layer bytecode 
encryption, obfuscation and tamper proofing. The Protector can also be 
useful for enhancing your server-side security or for protecting 
important business logic from leaking." [1].  The tool functions by 
encrypting Java class files in order to prevent attackers from de-
compiling the Java class files, and thus exposing the source code.   
 

-- Analysis -- 
 
The concept of encrypting Java class files to prevent de-compilition is 
fundamentally flawed because the Java Virtual Machine (JVM) cannot read 
encrypted class files.  It can only read files which comply with the 
well defined Java class file format [2].  Therefore, the encrypted class 
files have to be delivered to the JVM in the standard, unencrypted 
format.  An attacker who wishes to de-compile the class file can simply 
modify the Java class loader to extract the unencrypted class files 
[4][5].  These class files can then be decompiled using well known and 
freely available decompilation tools such as Jode [3]. 
 

-- Proof of Concept -- 

The following code[4] was inserted in the defineClass(String name, 
byte[] b, int off, int len, ProtectionDomain protectionDomain) method of 
the java/lang/ClassLoader.java file which is included in the JDK source 
code: 
  
if (!name.startsWith("java")) { 
  String baseDir = "/Users/stephen/dump";   
  String dirName = baseDir + File.separatorChar + 
name.substring(0,name.lastIndexOf(".")).replace('.', 
File.separatorChar); 
    File dir = new File(dirName); 
  dir.mkdirs(); 
  File dump = new File(baseDir + File.separatorChar + 
name.replace('.', File.separatorChar) + ".class"); 
  FileOutputStream out = null; 
  try { 
    out = new FileOutputStream (dump); 
    out.write (b, off, len); 
  } 
  catch (Exception e){ 
    e.printStackTrace (); 
  } 
  finally { 
    if (out != null) { 
      try { 
        out.close (); 
      } 
      catch (Exception e) { 
      } 
    } 
  } 
} 
 
This had the effect of writing the class file to a directory.  The 
modified ClassLoader.class file was included in the JVM runtime.   
The "Game of life" encrypted sample application was then loaded using 
the new modified JVM.  The raw class files were observed in the 
directory /Users/stephen/dump and these were loaded using Jode [3].  
Jode was successful in decompiling many of the important class files to 
the extent that functional process flow and constant values were 
exposed.  Some local variable names remained in obfuscated form, but 
these did not detract from the overall ability to view the source code.   
As an example, the following code is the original source code of the 
GameOfLifeCanvas constructor as provided with the sample application: 
 
public GameOfLifeCanvas(GameOfLifeGrid gameOfLifeGrid, int cellSize) { 
  this.gameOfLifeGrid = gameOfLifeGrid; 
  this.cellSize = cellSize; 
  gameOfLifeGrid.clear(); 
 
  addMouseListener( 
    new MouseAdapter() { 
      public void mouseReleased(MouseEvent e) { 
        draw(e.getX(), e.getY()); 
      } 
      public void mousePressed(MouseEvent e) { 
        saveCellUnderMouse(e.getX(), e.getY()); 
      } 
    }); 
 
  addMouseMotionListener(new MouseMotionAdapter() { 
    public void mouseDragged(MouseEvent e) { 
      draw(e.getX(), e.getY()); 
    } 
  }); 
} 
 
The same method as decompiled by Jode: 
 
public GameOfLifeCanvas(GameOfLifeGrid gameoflifegrid, int i) { 
  gameOfLifeGrid = gameoflifegrid; 
  cellSize = i; 
  gameoflifegrid.clear(); 
  this.addMouseListener(new MouseAdapter() { 
      public void mouseReleased(MouseEvent mouseevent) { 
    draw(mouseevent.getX(), mouseevent.getY()); 
      } 
       
      public void mousePressed(MouseEvent mouseevent) { 
    saveCellUnderMouse(mouseevent.getX(), mouseevent.getY()); 
      } 
  }); 
  this.addMouseMotionListener(new MouseMotionAdapter() { 
      public void mouseDragged(MouseEvent mouseevent) { 
    draw(mouseevent.getX(), mouseevent.getY()); 
      } 
  }); 
} 
 
 
-- Recommendations -- 
 
Simple class file encryption using a pure Java solution is a 
fundamentally flawed approach to protecting the intellectual property of 
software creators, and as this advisory shows it cannot be relied on to 
provide any protection from reverse engineering methods.  As a permanent 
solution to this issue consider re-architecting Java applications who's 
bytecode contains sensitive intellectual property so that the sensitive 
areas are executed in secured environments (such as on a server).  
Alternatively, consider strengthening the obfuscation mechanisms to 
delay decompilation of class files.  However, it should be noted that 
obfuscation will not provide a permanent solution to the problem, but 
will only delay a persistent attacker in obtaining the source code.   
 

-- CVE -- 
 
The Common Vulnerabilities and Exposures (CVE) project has assigned the 
name CVE-2007-0014 to this issue. This is a candidate for inclusion in 
the CVE list (http://cve.mitre.org), which standardises names for 
security problems. 
 
 
-- References -- 
 
[1] http://www.chainkey.com/en/jcp/ 
[2] http://java.sun.com/docs/books/vmspec/2nd-
edition/html/ClassFile.doc.html 
[3] http://jode.sourceforge.net 
[4] Sergey Edunov's post: http://lists.owasp.org/pipermail/java-
project/2006-October/000096.html 
[5] http://www.javaworld.com/javaworld/javaqa/2003-05/01-qa-0509-
jcrypt.html 
 

-- Revision -- 
 
a. Initial release. 
b. Released. 
 
 
 -- Distribution --

This security advisory may be freely distributed, provided that it 
remains unaltered and in its original form. 


-- Disclaimer --

The information contained within this advisory is supplied "as-is" with 
no warranties or guarantees of fitness of use or otherwise. Corsaire 
accepts no responsibility for any damage caused by the use or misuse of 
this information.


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