Android APK加壳技术方案代码实现

本文章由Jack_Jia编写，转载请注明出处。  

文章链接：http://blog.csdn.net/jiazhijun/article/details/8746917

作者：Jack_Jia    邮箱： 309zhijun@163.com

 一、序言

        在上篇“Android APK加壳技术方案”（http://blog.csdn.net/jiazhijun/article/details/8678399）博文中，根据加壳数据在解壳程序Dex文件所处的位置，我提出了两种Android Dex加壳技术实现方案，本片博文将对方案1代码实现进行讲解。博友可以根据方案1的代码实现原理对方案2自行实现。

       在方案1的代码实现过程中，各种不同的问题接踵出现，最初的方案也在不同问题的出现、解决过程中不断的得到调整、优化。

       本文的代码实现了对整个APK包的加壳处理。加壳程序不会对源程序有任何的影响。

二、代码实现

     本程序基于Android2.3代码实现，因为牵扯到系统代码的反射修改，本程序不保证在其它android版本正常工作，博友可以根据实现原理，自行实现对其它Android版本的兼容性开发。

     1、 加壳程序流程及代码实现

                  1、加密源程序APK为解壳数据

                  2、把解壳数据写入解壳程序DEX文件末尾，并在文件尾部添加解壳数据的大小。

                  3、修改解壳程序DEX头中checksum、signature 和file_size头信息。

       代码实现如下：

package com.android.dexshell;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.zip.Adler32;

public class DexShellTool {
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		try {
			File payloadSrcFile = new File("g:/payload.apk");
			File unShellDexFile = new File("g:/unshell.dex");
			byte[] payloadArray = encrpt(readFileBytes(payloadSrcFile));
			byte[] unShellDexArray = readFileBytes(unShellDexFile);
			int payloadLen = payloadArray.length;
			int unShellDexLen = unShellDexArray.length;
			int totalLen = payloadLen + unShellDexLen +4;
			byte[] newdex = new byte[totalLen];
			//添加解壳代码
			System.arraycopy(unShellDexArray, 0, newdex, 0, unShellDexLen);
			//添加加密后的解壳数据
			System.arraycopy(payloadArray, 0, newdex, unShellDexLen,
					payloadLen);
			//添加解壳数据长度
			System.arraycopy(intToByte(payloadLen), 0, newdex, totalLen-4, 4);
                        //修改DEX file size文件头
			fixFileSizeHeader(newdex);
			//修改DEX SHA1 文件头
			fixSHA1Header(newdex);
			//修改DEX CheckSum文件头
			fixCheckSumHeader(newdex);


			String str = "g:/classes.dex";
			File file = new File(str);
			if (!file.exists()) {
				file.createNewFile();
			}
			
			FileOutputStream localFileOutputStream = new FileOutputStream(str);
			localFileOutputStream.write(newdex);
			localFileOutputStream.flush();
			localFileOutputStream.close();


		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	//直接返回数据，读者可以添加自己加密方法
	private static byte[] encrpt(byte[] srcdata){
		return srcdata;
	}


	private static void fixCheckSumHeader(byte[] dexBytes) {
		Adler32 adler = new Adler32();
		adler.update(dexBytes, 12, dexBytes.length - 12);
		long value = adler.getValue();
		int va = (int) value;
		byte[] newcs = intToByte(va);
		byte[] recs = new byte[4];
		for (int i = 0; i < 4; i++) {
			recs[i] = newcs[newcs.length - 1 - i];
			System.out.println(Integer.toHexString(newcs[i]));
		}
		System.arraycopy(recs, 0, dexBytes, 8, 4);
		System.out.println(Long.toHexString(value));
		System.out.println();
	}


	public static byte[] intToByte(int number) {
		byte[] b = new byte[4];
		for (int i = 3; i >= 0; i--) {
			b[i] = (byte) (number % 256);
			number >>= 8;
		}
		return b;
	}


	private static void fixSHA1Header(byte[] dexBytes)
			throws NoSuchAlgorithmException {
		MessageDigest md = MessageDigest.getInstance("SHA-1");
		md.update(dexBytes, 32, dexBytes.length - 32);
		byte[] newdt = md.digest();
		System.arraycopy(newdt, 0, dexBytes, 12, 20);
		String hexstr = "";
		for (int i = 0; i < newdt.length; i++) {
			hexstr += Integer.toString((newdt[i] & 0xff) + 0x100, 16)
					.substring(1);
		}
		System.out.println(hexstr);
	}


	private static void fixFileSizeHeader(byte[] dexBytes) {


		byte[] newfs = intToByte(dexBytes.length);
		System.out.println(Integer.toHexString(dexBytes.length));
		byte[] refs = new byte[4];
		for (int i = 0; i < 4; i++) {
			refs[i] = newfs[newfs.length - 1 - i];
			System.out.println(Integer.toHexString(newfs[i]));
		}
		System.arraycopy(refs, 0, dexBytes, 32, 4);
	}


	private static byte[] readFileBytes(File file) throws IOException {
		byte[] arrayOfByte = new byte[1024];
		ByteArrayOutputStream localByteArrayOutputStream = new ByteArrayOutputStream();
		FileInputStream fis = new FileInputStream(file);
		while (true) {
			int i = fis.read(arrayOfByte);
			if (i != -1) {
				localByteArrayOutputStream.write(arrayOfByte, 0, i);
			} else {
				return localByteArrayOutputStream.toByteArray();
			}
		}
	}


}

    2、 解壳程序流程及代码实现

          在解壳程序的开发过程中需要解决如下几个关键的技术问题：

         （1）解壳代码如何能够第一时间执行？

                  Android程序由不同的组件构成，系统在有需要的时候启动程序组件。因此解壳程序必须在Android系统启动组件之前运行，完成对解壳数                据的解壳及APK文件的动态加载，否则会使程序出现加载类失败的异常。

                  Android开发者都知道Applicaiton做为整个应用的上下文，会被系统第一时间调用，这也是应用开发者程序代码的第一执行点。因此通过对              AndroidMainfest.xml的application的配置可以实现解壳代码第一时间运行。

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" android:name="com.android.dexunshell.ProxyApplication" >
    </application>

         （2）如何替换回源程序原有的Application?

                  当在AndroidMainfest.xml文件配置为解壳代码的Application时。源程序原有的Applicaiton将被替换，为了不影响源程序代码逻辑，我们需要              在解壳代码运行完成后，替换回源程序原有的Application对象。我们通过在AndroidMainfest.xml文件中配置原有Applicaiton类信息来达到我们              的目的。解壳程序要在运行完毕后通过创建配置的Application对象，并通过反射修改回原Application。

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" android:name="com.android.dexunshell.ProxyApplication" >
        <meta-data android:name="APPLICATION_CLASS_NAME" android:value="com.***.Application"/>
    </application>

          

          （3）如何通过DexClassLoader实现对apk代码的动态加载。

                  我们知道DexClassLoader加载的类是没有组件生命周期的，也就是说即使DexClassLoader通过对APK的动态加载完成了对组件类的加载，              当系统启动该组件时，还会出现加载类失败的异常。为什么组件类被动态加载入虚拟机，但系统却出现加载类失败呢？

                  通过查看Android源代码我们知道组件类的加载是由另一个ClassLoader来完成的，DexClassLoader和系统组件ClassLoader并不存在关                  系，系统组件ClassLoader当然找不到由DexClassLoader加载的类，如果把系统组件ClassLoader的parent修改成DexClassLoader，我们就可              以实现对apk代码的动态加载。

         （4）如何使解壳后的APK资源文件被代码动态引用。

                 代码默认引用的资源文件在最外层的解壳程序中，因此我们要增加系统的资源加载路径来实现对借壳后APK文件资源的加载。

        解壳实现代码：

package com.android.dexunshell;

import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;

import dalvik.system.DexClassLoader;
import android.app.Application;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.os.Bundle;

public class ProxyApplication extends Application {

	private static final String appkey = "APPLICATION_CLASS_NAME";
	private String apkFileName;
	private String odexPath;
	private String libPath;
	@Override
	public void onCreate() {
		// TODO Auto-generated method stub
		super.onCreate();
		try {
			File odex = this.getDir("payload_odex", MODE_PRIVATE);
			File libs = this.getDir("payload_lib", MODE_PRIVATE);
			odexPath = odex.getAbsolutePath();
			libPath = libs.getAbsolutePath();
			apkFileName = odex.getAbsolutePath()+"/payload.apk";
			File dexFile = new File(apkFileName);
			if(!dexFile.exists())
				dexFile.createNewFile();
			//读取程序classes.dex文件
			byte[] dexdata = this.readDexFileFromApk();
			//分离出解壳后的apk文件已用于动态加载
			this.splitPayLoadFromDex(dexdata);
			//配置动态加载环境
			this.configApplicationEnv();
			
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	private void configApplicationEnv() throws NameNotFoundException, IllegalAccessException, InstantiationException, ClassNotFoundException, IOException{ 

		Object currentActivityThread = RefInvoke.invokeStaticMethod("android.app.ActivityThread", "currentActivityThread", new Class[]{}, new Object[]{});
        HashMap mPackages = (HashMap)RefInvoke.getFieldOjbect("android.app.ActivityThread", currentActivityThread, "mPackages");
        //替换组件类加载器为DexClassLoader，已使动态加载代码具有组件生命周期
        WeakReference wr = (WeakReference) mPackages.get(this.getPackageName());
		DexClassLoader dLoader = new DexClassLoader(apkFileName,
				odexPath, libPath, (ClassLoader) RefInvoke.getFieldOjbect("android.app.LoadedApk", wr.get(), "mClassLoader"));
        RefInvoke.setFieldOjbect("android.app.LoadedApk", "mClassLoader", wr.get(), dLoader);

        //如果源应用配置有Appliction对象，则替换为源应用Applicaiton，以便不影响源程序逻辑。
		ApplicationInfo appInfo = this.getPackageManager().getApplicationInfo(this.getPackageName(),PackageManager.GET_META_DATA);
		Bundle bundle =  appInfo.metaData;
		if(bundle != null && bundle.containsKey(appkey)){
			
			String appClassName = bundle.getString(appkey);
			Application app = (Application)Class.forName(appClassName).newInstance();
			RefInvoke.setFieldOjbect("android.app.ContextImpl", "mOuterContext", this.getBaseContext(), app);
			RefInvoke.setFieldOjbect("android.content.ContextWrapper", "mBase", app, this.getBaseContext());
			Object mBoundApplication = RefInvoke.getFieldOjbect("android.app.ActivityThread", currentActivityThread, "mBoundApplication");
			Object info = RefInvoke.getFieldOjbect("android.app.ActivityThread$AppBindData", mBoundApplication, "info");
			RefInvoke.setFieldOjbect("android.app.LoadedApk", "mApplication", info, app);
			Object oldApplication = RefInvoke.getFieldOjbect("android.app.ActivityThread", currentActivityThread, "mInitialApplication");
			RefInvoke.setFieldOjbect("android.app.ActivityThread", "mInitialApplication", currentActivityThread, app);
			ArrayList<Application> mAllApplications = (ArrayList<Application>)RefInvoke.getFieldOjbect("android.app.ActivityThread", currentActivityThread, "mAllApplications");
			mAllApplications.remove(oldApplication);
			mAllApplications.add(app);
			HashMap mProviderMap = (HashMap) RefInvoke.getFieldOjbect("android.app.ActivityThread", currentActivityThread, "mProviderMap");
			Iterator it = mProviderMap.values().iterator();
			while(it.hasNext()){
				Object providerClientRecord = it.next();
				Object localProvider = RefInvoke.getFieldOjbect("android.app.ProviderClientRecord", providerClientRecord, "mLocalProvider");
				RefInvoke.setFieldOjbect("android.content.ContentProvider", "mContext", localProvider, app);
			}
			RefInvoke.invokeMethod(appClassName, "onCreate", app, new Class[]{}, new Object[]{});
		}
	}
	
	private void splitPayLoadFromDex(byte[] data) throws IOException{
		byte[] apkdata = decrypt(data);
		int ablen = apkdata.length;
		byte[] dexlen = new byte[4];
		System.arraycopy(apkdata, ablen - 4, dexlen, 0, 4);
		ByteArrayInputStream bais = new ByteArrayInputStream(dexlen);
		DataInputStream in = new DataInputStream(bais);
		int readInt = in.readInt();
		System.out.println(Integer.toHexString(readInt));
		byte[] newdex = new byte[readInt];
		System.arraycopy(apkdata, ablen - 4 - readInt, newdex, 0, readInt);
		File file = new File(apkFileName);
		try {
			FileOutputStream localFileOutputStream = new FileOutputStream(file);
			localFileOutputStream.write(newdex);
			localFileOutputStream.close();

		} catch (IOException localIOException) {
			throw new RuntimeException(localIOException);
		}
		
		ZipInputStream localZipInputStream = new ZipInputStream(
				new BufferedInputStream(new FileInputStream(file)));
		while (true) {
			ZipEntry localZipEntry = localZipInputStream.getNextEntry();
			if (localZipEntry == null) {
				localZipInputStream.close();
				break;
			}
			String name = localZipEntry.getName();
			if (name.startsWith("lib/") && name.endsWith(".so")) {
				File storeFile = new File(libPath+"/"+name.substring(name.lastIndexOf('/')));
				storeFile.createNewFile();
				FileOutputStream fos = new FileOutputStream(storeFile);
				byte[] arrayOfByte = new byte[1024];
				while (true) {
					int i = localZipInputStream.read(arrayOfByte);
					if (i == -1)
						break;
					fos.write(arrayOfByte, 0, i);
				}
				fos.flush();
				fos.close();	
			}
			localZipInputStream.closeEntry();
		}
		localZipInputStream.close();	
		
	}
	
	private byte[] readDexFileFromApk() throws IOException {
		ByteArrayOutputStream dexByteArrayOutputStream = new ByteArrayOutputStream();
		ZipInputStream localZipInputStream = new ZipInputStream(
				new BufferedInputStream(new FileInputStream(this.getApplicationInfo().sourceDir)));
		while (true) {
			ZipEntry localZipEntry = localZipInputStream.getNextEntry();
			if (localZipEntry == null) {
				localZipInputStream.close();
				break;
			}
			if (localZipEntry.getName().equals("classes.dex")) {
				byte[] arrayOfByte = new byte[1024];
				while (true) {
					int i = localZipInputStream.read(arrayOfByte);
					if (i == -1)
						break;
					dexByteArrayOutputStream.write(arrayOfByte, 0, i);
				}
			}
			localZipInputStream.closeEntry();
		}
		localZipInputStream.close();
		return dexByteArrayOutputStream.toByteArray();
	}
	
	////直接返回数据，读者可以添加自己解密方法
	private byte[] decrypt(byte[] data){
		return data;
	}
}

        RefInvoke为反射调用工具类：

package com.android.dexunshell;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class RefInvoke {
	
	public static  Object invokeStaticMethod(String class_name, String method_name, Class[] pareTyple, Object[] pareVaules){
		
		try {
			Class obj_class = Class.forName(class_name);
			Method method = obj_class.getMethod(method_name,pareTyple);
			return method.invoke(null, pareVaules);
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}  catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchMethodException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return null;
		
	}
	
	public static  Object invokeMethod(String class_name, String method_name, Object obj ,Class[] pareTyple, Object[] pareVaules){
		
		try {
			Class obj_class = Class.forName(class_name);
			Method method = obj_class.getMethod(method_name,pareTyple);
			return method.invoke(obj, pareVaules);
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}  catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchMethodException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return null;
		
	}
	
	public static Object getFieldOjbect(String class_name,Object obj, String filedName){
		try {
			Class obj_class = Class.forName(class_name);
			Field field = obj_class.getDeclaredField(filedName);
			field.setAccessible(true);
			return field.get(obj);
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchFieldException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return null;
		
	}
	
	public static Object getStaticFieldOjbect(String class_name, String filedName){
		
		try {
			Class obj_class = Class.forName(class_name);
			Field field = obj_class.getDeclaredField(filedName);
			field.setAccessible(true);
			return field.get(null);
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchFieldException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return null;
		
	}
	
	public static void setFieldOjbect(String classname, String filedName, Object obj, Object filedVaule){
		try {
			Class obj_class = Class.forName(classname);
			Field field = obj_class.getDeclaredField(filedName);
			field.setAccessible(true);
			field.set(obj, filedVaule);
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchFieldException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}	
	}
	
	public static void setStaticOjbect(String class_name, String filedName, Object filedVaule){
		try {
			Class obj_class = Class.forName(class_name);
			Field field = obj_class.getDeclaredField(filedName);
			field.setAccessible(true);
			field.set(null, filedVaule);
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchFieldException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}		
	}

}

三、总结

       本文代码基本实现了APK文件的加壳及脱壳原理，该代码作为实验代码还有诸多地方需要改进。比如：

             1、加壳数据的加密算法的添加。

             2、脱壳代码由java语言实现，可通过C代码的实现对脱壳逻辑进行保护，以达到更好的反逆向分析效果。