Android杂谈---用MD5处理明文密码

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。

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下面是个小例子：

main.xml

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<?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"    ><EditTextandroid: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"/><EditTextandroid: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"/><Buttonandroid: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"/><Buttonandroid: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

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<?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

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package com.loulijun.md5demo;import android.app.Activity;import android.os.Bundle;public class Login extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);setContentView(R.layout.login);}}

?MD5Demo.java

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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()        {@Overridepublic 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()        {                @Overridepublic 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：

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