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：
