How do I use ProGuard?

Question

I was trying to learn how to use ProGuard, and it is no way as easy as I thought. At first I found a simple Java code to try it, a simple two class Swing calculator.

The code can be found by following that link, but I found it too verbose to post the it here. Anyway, it is a plain application with entry point on Calc.main(), there are no packages.

Then I compiled both sources with:

$ javac *.java

and created the .jar file (because it seems ProGuard only work with jars):

$ jar cvef Calc calc.jar *.class
added manifest
adding: Calc.class(in = 3869) (out= 2126)(deflated 45%)
adding: Calc$ClearListener.class(in = 468) (out= 327)(deflated 30%)
adding: CalcLogic.class(in = 1004) (out= 515)(deflated 48%)
adding: Calc$NumListener.class(in = 1005) (out= 598)(deflated 40%)
adding: Calc$OpListener.class(in = 1788) (out= 1005)(deflated 43%)

Wrote the ProGuard file named obfuscate.pro:

-injars       calc.jar
-outjars      calc_obf.jar
-libraryjars  <java.home>/lib/rt.jar

-keep public class Calc extends javax.swing.JFrame {
public static void main(java.lang.String[]);
}

And finally run ProGuard:

$ ~/progs/proguard/proguard4.8/bin/proguard.sh @obfuscate.pro
ProGuard, version 4.8
Reading program jar [/home/lucas/tmp/calc.jar]
Reading library jar [/usr/lib/jvm/java-7-openjdk-i386/jre/lib/rt.jar]
Error: The output jar is empty. Did you specify the proper '-keep' options?

Well, obviously didn't work. I got tired of messing with ProGruard parameters, specially with that -keep options, with no success. All I found in the docs related to my problem could not help me. Then I am resorting to you... What is wrong? How to do it right?

Answer 1

Here is solution with gradle

1. Create a runnable jar with all dependent libraries copied to a directory "dependencies" and add the classpath in the manifest.

   task createJar(type: Jar) {
      println("Cleaning...")
      clean
      manifest {
      attributes('Main-Class': 'com.abc.gradle.hello.App',
        'Class-Path': configurations.default.collect { 'dependencies/' + 
         it.getName() }.join(' ')
         )
      }
      from {
         configurations.compile.collect { it.isDirectory() ? it : zipTree(it) 
         }
      } with jar
      println "${outputJar} created"
      }
   

2. Copy the dependencies

   task copyDepends(type: Copy) {
     from configurations.default
     into "${dependsDir}"
   }
   

3. Obfuscate the library with Proguard

   task proguard(type: proguard.gradle.ProGuardTask) {
      println("Performing obfuscation..")
      configuration 'proguard.conf'
      injars "${outputJar}"
      outjars "${buildDir}/libs/${rootProject.name}_proguard.jar"
      libraryjars "${System.getProperty('java.home')}/lib/rt.jar"
      libraryjars "${dependsDir}"
    }
   

Here is the complete build.gradle

buildscript {
 repositories {
    mavenCentral()
 }
 dependencies {
    classpath 'net.sf.proguard:proguard-gradle:6.0.3'
    classpath 'net.sf.proguard:proguard-base:6.0.3'
 }
}

plugins {
 id 'java'
 id 'application'
}

repositories {
  mavenCentral()
}

dependencies {
   implementation 'org.slf4j:slf4j-api:1.7.30'
   implementation 'ch.qos.logback:logback-classic:1.2.3'
   implementation 'ch.qos.logback:logback-core:1.2.3'
   testImplementation 'junit:junit:4.13'
}

def outputJar = "${buildDir}/libs/${rootProject.name}.jar"
def dependsDir = "${buildDir}/libs/dependencies/"
def runnableJar = "${rootProject.name}_fat.jar";

task copyDepends(type: Copy) {
 from configurations.default
 into "${dependsDir}"
}

task createJar(type: Jar) {
 println("Cleaning...")
 clean
 manifest {
    attributes('Main-Class': 'com.abc.gradle.hello.App',
            'Class-Path': configurations.default.collect { 'dependencies/' + 
   it.getName() }.join(' ')
    )
  }
  from {
    configurations.compile.collect { it.isDirectory() ? it : zipTree(it) }
   } with jar
   println "${outputJar} created"
  }

task proguard(type: proguard.gradle.ProGuardTask) {
   println("Performing obfuscation..")
   configuration 'proguard.conf'
   injars "${outputJar}"
   outjars "${buildDir}/libs/${rootProject.name}_proguard.jar"

   libraryjars "${System.getProperty('java.home')}/lib/rt.jar"
   libraryjars "${dependsDir}"

  }

Proguard.conf

-keep public class * {
   public * ;
 }

Gradle commands to obfuscate

gradle createJar
gradle copyDepends
gradle proguard

Answer 2

I've had similar problems, solved by taking out Java modifiers.

Java modifiers such as visibility modifiers are optional in the ProGuard configuration file -keep option (and in related options -keepclassmembers etc.)

From manual: -keep [,modifier,...] class_specification

So unless there is a specific reason otherwise, you can leave them out.

Answer 3

I got it to work using the following configuration file:

-injars       calc.jar
-outjars      calc_obf.jar
-libraryjars  <java.home>/lib/rt.jar
-keep class Calc {
  public static void main(java.lang.String[]);
}

Most notably, I ditched the public in front of class Calc.