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。

 

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：