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 Android教程網 >> Android技術 >> 關於Android編程 >> 為Android的apk應用程序文件加殼以防止反編譯的教程

為Android的apk應用程序文件加殼以防止反編譯的教程

編輯:關於Android編程

一、什麼是加殼?
加殼是在二進制的程序中植入一段代碼,在運行的時候優先取得程序的控制權,做一些額外的工作。大多數病毒就是基於此原理。

二、加殼作用
加殼的程序可以有效阻止對程序的反匯編分析,以達到它不可告人的目的。這種技術也常用來保護軟件版權,防止被軟件破解。

三、Android Dex文件加殼原理
PC平台現在已存在大量的標准的加殼和解殼工具,但是Android作為新興平台還未出現APK加殼工具。Android Dex文件大量使用引用給加殼帶來了一定的難度,但是從理論上講,Android APK加殼也是可行的。
在這個過程中,牽扯到三個角色:
1、加殼程序:加密源程序為解殼數據、組裝解殼程序和解殼數據
2、解殼程序:解密解殼數據,並運行時通過DexClassLoader動態加載
3、源程序:需要加殼處理的被保護代碼
根據解殼數據在解殼程序DEX文件中的不同分布,本文將提出兩種Android Dex加殼的實現方案。

解殼數據位於解殼程序文件尾部:該種方式簡單實用,合並後的DEX文件結構如下。

2016428142304174.png (242×541)

四、加殼程序工作流程:
1、加密源程序APK文件為解殼數據
2、把解殼數據寫入解殼程序Dex文件末尾,並在文件尾部添加解殼數據的大小。
3、修改解殼程序DEX頭中checksum、signature 和file_size頭信息。
4、修改源程序AndroidMainfest.xml文件並覆蓋解殼程序AndroidMainfest.xml文件。

五、解殼DEX程序工作流程:
1、讀取DEX文件末尾數據獲取借殼數據長度。
2、從DEX文件讀取解殼數據,解密解殼數據。以文件形式保存解密數據到a.APK文件
3、通過DexClassLoader動態加載a.apk。

解殼數據位於解殼程序文件頭
該種方式相對比較復雜, 合並後DEX文件結構如下:

2016428142331268.png (241×526)

六、加殼程序工作流程:
1、加密源程序APK文件為解殼數據
2、計算解殼數據長度,並添加該長度到解殼DEX文件頭末尾,並繼續解殼數據到文件頭末尾。
(插入數據的位置為0x70處)
3、修改解殼程序DEX頭中checksum、signature、file_size、header_size、string_ids_off、type_ids_off、proto_ids_off、field_ids_off、
method_ids_off、class_defs_off和data_off相關項。  分析map_off 數據,修改相關的數據偏移量。 
4、修改源程序AndroidMainfest.xml文件並覆蓋解殼程序AndroidMainfest.xml文件。

七、加殼程序流程及代碼實現
1、加密源程序APK為解殼數據
2、把解殼數據寫入解殼程序DEX文件末尾,並在文件尾部添加解殼數據的大小。
3、修改解殼程序DEX頭中checksum、signature 和file_size頭信息。

代碼實現如下:

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]; 
   //添加解殼代碼 
   System.arraycopy(unShellDexArray, 0, newdex, 0, unShellDexLen); 
   //添加加密後的解殼數據 
   System.arraycopy(payloadArray, 0, newdex, unShellDexLen, 
     payloadLen); 
   //添加解殼數據長度 
   System.arraycopy(intToByte(payloadLen), 0, newdex, totalLen-4, 4); 
      //修改DEX file size文件頭 
   fixFileSizeHeader(newdex); 
   //修改DEX SHA1 文件頭 
   fixSHA1Header(newdex); 
   //修改DEX CheckSum文件頭 
   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(); 
  } 
 } 
  
 //直接返回數據,讀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(); 
   } 
  } 
 } 
 
 
} 


八、解殼程序流程及代碼實現
在解殼程序的開發過程中需要解決如下幾個關鍵的技術問題:
1.解殼代碼如何能夠第一時間執行?
Android程序由不同的組件構成,系統在有需要的時候啟動程序組件。因此解殼程序必須在Android系統啟動組件之前運行,完成對解殼數據的解殼及APK文件的動態加載,否則會使程序出現加載類失敗的異常。
Android開發者都知道Applicaiton做為整個應用的上下文,會被系統第一時間調用,這也是應用開發者程序代碼的第一執行點。因此通過對AndroidMainfest.xml的application的配置可以實現解殼代碼第一時間運行。

<application 
 android:icon="@drawable/ic_launcher" 
 android:label="@string/app_name" 
 android:theme="@style/AppTheme" android:name=" 

</application> 

2.如何替換回源程序原有的Application?
當在AndroidMainfest.xml文件配置為解殼代碼的Application時。源程序原有的Applicaiton將被替換,為了不影響源程序代碼邏輯,我們需要              在解殼代碼運行完成後,替換回源程序原有的Application對象。我們通過在AndroidMainfest.xml文件中配置原有Applicaiton類信息來達到我們              的目的。解殼程序要在運行完畢後通過創建配置的Application對象,並通過反射修改回原Application。

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

3.如何通過DexClassLoader實現對apk代碼的動態加載。
我們知道DexClassLoader加載的類是沒有組件生命周期的,也就是說即使DexClassLoader通過對APK的動態加載完成了對組件類的加載,當系統啟動該組件時,還會出現加載類失敗的異常。為什麼組件類被動態加載入虛擬機,但系統卻出現加載類失敗呢?
通過查看Android源代碼我們知道組件類的加載是由另一個ClassLoader來完成的,DexClassLoader和系統組件ClassLoader並不存在關系,系統組件ClassLoader當然找不到由DexClassLoader加載的類,如果把系統組件ClassLoader的parent修改成DexClassLoader,我們就可以實現對apk代碼的動態加載。

4.如何使解殼後的APK資源文件被代碼動態引用。
代碼默認引用的資源文件在最外層的解殼程序中,因此我們要增加系統的資源加載路徑來實現對借殼後APK文件資源的加載。

解殼實現代碼:
 

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(); 
   //讀取程序classes.dex文件 
   byte[] dexdata = this.readDexFileFromApk(); 
   //分離出解殼後的apk文件已用於動態加載 
   this.splitPayLoadFromDex(dexdata); 
   //配置動態加載環境 
   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"); 
  //替換組件類加載器為DexClassLoader,已使動態加載代碼具有組件生命周期 
  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); 
 
  //如果源應用配置有Appliction對象,則替換為源應用Applicaiton,以便不影響源程序邏輯。 
  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)dLoader.loadClass(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(); 
 } 
  
 ////直接返回數據,讀者可以添加自己解密方法 
 private byte[] decrypt(byte[] data){ 
  return data; 
 } 
} 

RefInvoke為反射調用工具類:

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(); 
  }   
 } 
 
} 


九、總結
本文代碼基本實現了APK文件的加殼及脫殼原理,該代碼作為實驗代碼還有諸多地方需要改進。比如:
1、加殼數據的加密算法的添加。
2、脫殼代碼由java語言實現,可通過C代碼的實現對脫殼邏輯進行保護,以達到更好的反逆向分析效果。

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