很多的網絡相關的軟件都需要用戶名密碼登錄，在開發的時候像這些密碼都是保存在SharedPreferences中，這些密碼保存在/data/data/包名/shared_prefs下，保存在一個XML文件中，如下：
可以用FileBrower查看
開始說道正題，MD5加密算法雖然現在有些人已經將其解開了，但是它的加密機制依然很強大，我想絕大對數還是不會解開的。MD5加密算法是單向加密，只能用你的密碼才能解開，要不就是會解密算法，否則想都別想解開。爲了防止這種情況的發生。還可以對加密過的密碼進行再次加密。
下面是個小例子：
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"
- >
- <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="帳號"
- />
- <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="密碼"
- />
- <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="登錄"
- />
- </LinearLayout>
<?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="帳號"
/>
<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="密碼"
/>
<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="登錄"
/>
</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>
<?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 {
- @Override
- protected void onCreate(Bundle savedInstanceState) {
- // TODO Auto-generated method stub
- super.onCreate(savedInstanceState);
- setContentView(R.layout.login);
- }
- }
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
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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()
- {
- @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(), "密碼不能爲空！", 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(), "密碼是錯誤的！", Toast.LENGTH_LONG).show();
- }
- }else
- {
- Toast.makeText(getApplicationContext(), "密碼不能爲空！", 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;
- }
- }
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(), "密碼不能爲空！", 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(), "密碼是錯誤的！", Toast.LENGTH_LONG).show();
}
}else
{
Toast.makeText(getApplicationContext(), "密碼不能爲空！", 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;
}
}程序很簡單，下面是運行的效果：
