Android 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：

选用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。

java代码：

<?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 eoe.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 eoe.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;
}

}