Code obfuscation under Android programming

What is code obfuscation

Java is a cross-platform, interpreted language in which Java source code is compiled into an intermediate "bytecode" stored in a class file. Because of the cross-platform requirements, Java bytecode contains a lot of source code information, such as variable name, method name, and through these names to access variables and methods, these symbols with a lot of semantic information, it is easy to decompile the Java source code. To prevent this, we can use Java obfuscation to confuse Java bytecode.

Confusion is the re-organization and processing of the published program, so that the processed code and the pre-processing code to complete the same function, and the confusing code is difficult to decompile, even if the anti-compilation success is difficult to derive the true semantics of the program. The obfuscated program code, still in accordance with the original file format and instruction set, the execution result is the same as before, but the confusion of all the variables, functions, classes in the code to the name of the short English letter code, in the absence of the corresponding function name and program comments, even if it is anti-compilation, it will be difficult to read. At the same time confusion is irreversible, in the process of confusion, some information that does not affect the normal operation will be lost permanently, the loss of this information makes the program more difficult to understand.

The role of the obfuscation is not only to protect the code, it also has the function of simplifying the size of the compiled program. Because of the shortened variables and function names described above, and the reasons for missing some information, the size of the jar file can be reduced by approximately 25%, which makes sense for the current cost of the wireless network transmission is more expensive.

Confusing file proguard.cfg parameters

-optimizationpasses 5                                                              #  specifies the compression level of the Code-dontusemixedcaseclassnames                                                        #  Whether to use case mixed-dontskipnonpubliclibraryclasses                                     &Whether nbsp;            #  is confusing third party jar-dontpreverify                                                                      #  whether to do pre-calibration when confusing-verbose                                                                            #  If the log is logged when confused-optimizations !code/simplification/arithmetic,!field/*,!class/merging/*        #  The algorithm used in the confusion is-keep public class * extends android.app.activity                                 #  maintain which classes are not confused-keep public class *  extends android.app.Application                             #  Keep What classes are not confused-keep public class * extends android.app.service                                  #  maintain which classes are not confused-keep public class  * extends android.conTent. broadcastreceiver                   #  maintain which classes are not confused-keep public class * extends  android.content.contentprovider                     #  maintain which classes are not confused-keep public class * extends  android.app.backup.BackupAgentHelper                #  maintain which classes are not confused-keep public class * extends  android.preference.preference                       #  maintain which classes are not confused-keep public class  com.android.vending.licensing.ilicensingservice               #  maintain which classes are not confused-keepclasseswithmembernames class * {                                             #  Keep  native  method not to be confused     native <methods>;} -keepclasseswithmembers class * {                                                  #  Keep custom control classes from being confused     public <init> (android.content.context,  Android.util.AttributeSet);} -keepclasseswithmembers class * {    public <init> ( Android.content.context, android.util.attributeset, int);      #  Keep custom control classes from being confused}-keepclassmembers class * extends  android.app.activity {                         #  Keep custom control classes from being confused    public  void * (Android.view.View);} -keepclassmembers enum * {                                                         #  Keep enumerations  enum  classes from being confused     public  Static **[] values ();     public static ** valueof ( java.lang.String);} -keep class * implements android.os.parcelable {                                 #  Keep  Parcelable  not be confused   public  static final android.os.parcelable$creator *;} -keep class myclass;                                                               #  keep your defined classes from being confused

Method of code obfuscation

Depending on the version of the SDK, there are 2 different ways of confusing code, the information involved in the PROGUARD.CFG parameter details above is a confusing script under the lower version of the SDK , in fact, in the higher version of the SDK The principle and parameters of the confusion are similar to those of the lower versions, except that the confusing scripts are introduced in different versions of the SDK . Here's how:

• Low versionSDK, the project contains bothproguard.cfgAndproject.propertiesFile, you only need to project.properties fileAdd at the endProguard. config=proguard.cfg to export the project again.

• High versionSDK, the project contains bothProguard-project.txtAndproject.propertiesfile, you need to proguard-project.txt Configuration of the following information in the file, and thenthen export the project to。 The following is a demonstration of a real file.

 # this file is automatically generated by android tools.# do  not modify this file -- your changes will be erased!##  this file must be checked in version control systems.## to  customize properties used by the Ant build system edit#  " Ant.properties ",  and override values to adapt the script to your#  project structure.## to enable proguard to shrink and obfuscate  your code, uncomment this  (available properties: sdk.dir, user.home): #proguard. Config=${sdk.dir}/tools/proguard/proguard-android.txt:proguard-project.txtproguard.config=${sdk.dir} /tools/proguard/proguard-android.txt:proguard-project.txt# project target.target=android-16 

 project.properties   The contents of the file, the blue text is the configuration information we need to add during the code obfuscation, where: sdk.dir   is the installation path for your SDK on the current machine If you want to keep a file under a package is not confused, you can  proguard-project.txt The   file is added with a statement that retains the corresponding package name.

# to enable proguard in your project, edit project.properties# to  define the proguard.config property as described in that file.##  Add project specific ProGuard rules here.# By default, the  flags in this file are appended to flags specified# in ${ Sdk.dir}/tools/proguard/proguard-android.txt# you can edit the include path  and order by changing the ProGuard# include property in  Project.properties.## for more details, see#   http://developer.android.com /guide/developing/tools/proguard.html# add any project specific keep options  here:-dontwarn com.cnki.android.cnkireader.** -keep class  com.cnki.android.cnkireader.** { *; }# if your project uses webview with js, uncomment the  Following# and specify the fully qualified class name to the  JavaScript interface# class:#-keepclassmembers class  fqcn.of.javascript.interface.for.webview {#   public *;#}