主题：Android杂谈---用MD5加密算法加密密码（转载）

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：