RetroGuard is an extremely competent obfuscator for compiled Java classes. It is also an open source, extremely competent obfuscator for compiled Java classes. The source code changes explained here subvert RetroGuard into being a quasi code deobfuscator, in that it will assign random nouns (animal names, in this case) to obfuscated Java class field names, and random English verbs to obfuscated Java class method names. For more background on this experiment, read the following entries from the Breaking Eggs and Making Omelettes blog:

• Reverse Engineering/Java Category
• Automated Java De-obfuscation
• Success On The Java De-obfuscation Front
• Chaos Works In Strange Ways

I am not that talented with Java development, so this explanation is the best I can do for those interested in running this experiment:

1. download the Java Development Kit From Sun and install it
2. download the Apache Ant distribution and install it
   • note that when I did this, I installed the library in c:\ant (under Windows, naturally); further, I found it necessary to 'jar xf *.jar' all of the .jar library files for the distribution
3. download the RetroGuard package (either .zip or .tar.gz)
4. unpack the RetroGuard package
5. unpack the "src-dist" source code package
6. change into the src-dist/ directory
7. time to apply the changes:
   1. download the NounNameMaker.java file and place it in COM/rl/obf
   2. download the VerbNameMaker.java file and place it in COM/rl/obf
   3. edit COM/rl/obf/Cl.java and find the following lines:

                  // Create new name-makers for the namespace
                  methodNameMaker = new KeywordNameMaker(methodNames);
                  fieldNameMaker = new KeywordNameMaker(fieldNames);
      

      replace with:

                  // Create new name-makers for the namespace
                  methodNameMaker = new VerbNameMaker(methodNames);
                  fieldNameMaker = new NounNameMaker(fieldNames);
      

   4. recompile; if you are developing under Windows, try this quick batch file:

      javac.exe *.java
      javac.exe -classpath .;c:\ant\lib COM\rl\ant\*.java
      javac.exe COM\rl\obf\*.java
      javac.exe COM\rl\obf\classfile\*.java
      javac.exe COM\rl\obf\gui\*.java
      javac.exe COM\rl\obf\patch\*.java
      javac.exe COM\rl\util\*.java
      javac.exe COM\rl\util\rfc822\*.java
      

   5. run the program as normal against a Java jar archive:

      java RetroGuard infile.jar outfile-deobf.jar
      

Some notes about the experiment:

• The NounNameMaker and VerbNameMaker classes both have a constant random seed ("private static final int randomSeed = 6;"). This ensures that the classes will generate the same sequence of random identifiers on each run. Change the seed if you want to change the sequence.
• The driving purpose of this experiment was to rename simple 1- and 2- character identifiers and nonsense, reserved-word method names with real nouns and verbs that are easier to work with, psychologically. If English is not your first language, you may consider substituting the noun or verb lists with ones from your native language. For verbs, check out verba.org for extensive lists of verbs in numerous languages.

I would distribute a compiled Java jar file on this page except that I cannot figure out how to make a functioning jar file. If any Java ninjas want to help me with this, please email. If you have any trouble with these instructions, please send me an email and we will work through them.

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