主题：Android杂谈---用MD5加密算法加密密码

很多的网络相关的软件都需要用户名密码登录，在开发的时候像这些密码都是保存在SharedPreferences中，这些密码保存在/data/data/包名/shared_prefs下，保存在一个XML文件中，如下：

可以用FileBrower查看

开始说道正题，MD5加密算法虽然现在有些人已经将其解开了，但是它的加密机制依然很强大，我想绝大对数还是不会解开的。MD5加密算法是单向加 密，只能用你的密码才能解开，要不就是会解密算法，否则想都别想解开。为了防止这种情况的发生。还可以对加密过的密码进行再次加密。

 

下面是个小例子：

main.xml

 

 <?xml version= "1.0"  encoding= "utf-8" ?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:orientation="vertical"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
     >
     <EditText
         android:id="@+id/username"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:layout_marginLeft="10dp"
         android:layout_marginTop="20dp"
         android:layout_marginRight="10dp"
         android:hint="帐号"
     />
     <EditText
         android:id="@+id/password"
         android:password="true"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:layout_marginLeft="10dp"
         android:layout_marginTop="10dp"
         android:layout_marginRight="10dp"
         android:hint="密码"
     />
     <Button
         android:id="@+id/save"
         android:text="保存"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:layout_marginLeft="10dp"
         android:layout_marginTop="10dp"
         android:layout_marginRight="10dp"
     />
     <Button
         android:id="@+id/login"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:layout_marginLeft="10dp"
         android:layout_marginTop="10dp"
         android:layout_marginRight="10dp"
         android:text="登录"
     />
 </LinearLayout>

 login.xml

 

 <?xml version= "1.0"  encoding= "utf-8" ?>
 <LinearLayout
   xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:orientation="vertical" >
   <TextView
     android:layout_width="fill_parent"
     android:layout_height="wrap_content"
     android:text="login successful!"
   />
 </LinearLayout>

 login.java

 

 package  com.loulijun.md5demo;

 import  android.app.Activity;
 import  android.os.Bundle;

 public   class  Login  extends  Activity {

     @Override
     protected   void  onCreate(Bundle savedInstanceState) {
         // TODO Auto-generated method stub
         super .onCreate(savedInstanceState);
         setContentView(R.layout.login);
     }

 }

 MD5Demo.java

 

 package  com.loulijun.md5demo;

 import  java.security.MessageDigest;

 import  android.app.Activity;
 import  android.content.Intent;
 import  android.content.SharedPreferences;
 import  android.os.Bundle;
 import  android.view.View;
 import  android.widget.Button;
 import  android.widget.EditText;
 import  android.widget.Toast;

 public   class  MD5Demo  extends  Activity {
     private  EditText username,password;
     private  Button savebtn,loginbtn;
     String user,pass;
     @Override
     public   void  onCreate(Bundle savedInstanceState) {
         super .onCreate(savedInstanceState);
         setContentView(R.layout.main);
         username = (EditText)findViewById(R.id.username);
         password = (EditText)findViewById(R.id.password);
         savebtn = (Button)findViewById(R.id.save);
         loginbtn = (Button)findViewById(R.id.login);

         savebtn.setOnClickListener(new  Button.OnClickListener()
         {

             @Override
             public   void  onClick(View v) {
                 SharedPreferences pre = getSharedPreferences("loginvalue" ,MODE_WORLD_WRITEABLE);
                 pass = MD5(password.getText().toString());
                 user = username.getText().toString();
                 if (!pass.equals( "" )&&!user.equals( "" ))
                 {
                       pre.edit().putString("username" , username.getText().toString()).
                       putString("password" ,encryptmd5(pass)).commit();
                       Toast.makeText(getApplicationContext(), "保存成功!" , Toast.LENGTH_SHORT).show();
                 }else
                 {
                     Toast.makeText(getApplicationContext(), "密码不能为空！" , Toast.LENGTH_LONG).show();
                 }


             }

         });
         loginbtn.setOnClickListener(new  Button.OnClickListener()
         {


             @Override
             public   void  onClick(View v) {
                 SharedPreferences sp = getSharedPreferences("loginvalue" , MODE_WORLD_READABLE);
                 String loginuser = sp.getString("username" ,  null );
                 String loginpass = sp.getString("password" ,  null );

                 user = username.getText().toString();
                 pass = password.getText().toString();

                 String passmd5 = MD5(pass);
                 String encryptmd5 = encryptmd5(passmd5);

                 System.out.println("username=" +loginuser+ "-------------password=" +loginpass);
                   System.out.println("user==" +user+ "-------------encryptmd5==" +encryptmd5);
                   if (!user.equals( "" )&&!pass.equals( "" ))
                   {
                       if ( user.equals(loginuser)&& encryptmd5.equals(loginpass))
                       {
                           Intent intent = new  Intent();
                           intent.setClass(MD5Demo.this , Login. class );
                           MD5Demo.this .startActivity(intent);
                           finish();
                       }else
                       {
                           Toast.makeText(getApplicationContext(), "密码是错误的！" , Toast.LENGTH_LONG).show();
                       }
                   }else
                   {
                       Toast.makeText(getApplicationContext(), "密码不能为空！" , Toast.LENGTH_LONG).show();
                   }

             }

         });
     }

   //MD5加密，32位
     public   static  String MD5(String str)
     {
         MessageDigest md5 = null ;
         try
         {
             md5 = MessageDigest.getInstance("MD5" );
         }catch (Exception e)
         {
             e.printStackTrace();
             return   "" ;
         }

         char [] charArray = str.toCharArray();
         byte [] byteArray =  new   byte [charArray.length];

         for ( int  i =  0 ; i < charArray.length; i++)
         {
             byteArray[i] = (byte )charArray[i];
         }
         byte [] md5Bytes = md5.digest(byteArray);

         StringBuffer hexValue = new  StringBuffer();
         for (  int  i =  0 ; i < md5Bytes.length; i++)
         {
             int  val = (( int )md5Bytes[i])& 0xff ;
             if (val <  16 )
             {
                 hexValue.append("0" );
             }
             hexValue.append(Integer.toHexString(val));
         }
         return  hexValue.toString();
     }

     // 可逆的加密算法
     public   static  String encryptmd5(String str) {
         char [] a = str.toCharArray();
         for  ( int  i =  0 ; i < a.length; i++)
         {
                 a[i] = (char ) (a[i] ^  'l' );
         }
         String s = new  String(a);
         return  s;
     }

 }

 程序很简单，下面是运行的效果：