【平台开发】-Android使用MD5加密算法加密密码

很多的Android软件都需要用户登录登录功能，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，Android 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:layout_width = "fill_parent"
android:layout_height = "wrap_content"
android:layout_marginLeft = "10dp"
android:layout_marginTop = "10dp"
android:layout_marginRight = "10dp"
android:text = "保存" />
< 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;
}

}

加密密码程序很简单，下面是运行的效果：