Question

我使用Base64在sharedpreferences中加密了字符串但我的解码错误了。我是加密新手，无法确定logcat错误。

logcat的：

  11-12 03:57:06.593: W/System.err(20229): java.lang.NullPointerException: Input string was null.
  11-12 03:57:06.603: W/System.err(20229):  at com.SharedPreferences.Login.Base64.decode(Base64.java:1243)
  11-12 03:57:06.603: W/System.err(20229):  at com.SharedPreferences.Login.Base64.decode(Base64.java:1224)
  11-12 03:57:06.603: W/System.err(20229):  at com.SharedPreferences.Login.AccessApp.decrypt(AccessApp.java:137)
  11-12 03:57:06.603: W/System.err(20229):  at com.SharedPreferences.Login.AccessApp.onClick(AccessApp.java:55)
  11-12 03:57:06.603: W/System.err(20229):  at android.view.View.performClick(View.java:3511)
  11-12 03:57:06.613: W/System.err(20229):  at android.view.View$PerformClick.run(View.java:14105)
  11-12 03:57:06.635: W/System.err(20229):  at android.os.Handler.handleCallback(Handler.java:605)
  11-12 03:57:06.643: W/System.err(20229):  at android.os.Handler.dispatchMessage(Handler.java:92)
  11-12 03:57:06.669: W/System.err(20229):  at android.os.Looper.loop(Looper.java:137)
  11-12 03:57:06.673: W/System.err(20229):  at android.app.ActivityThread.main(ActivityThread.java:4424)
  11-12 03:57:06.673: W/System.err(20229):  at java.lang.reflect.Method.invokeNative(Native Method)
  11-12 03:57:06.673: W/System.err(20229):  at java.lang.reflect.Method.invoke(Method.java:511)
  11-12 03:57:06.695: W/System.err(20229):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
  11-12 03:57:06.695: W/System.err(20229):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
  11-12 03:57:06.695: W/System.err(20229):  at dalvik.system.NativeStart.main(Native Method)

类检索保存字符串并解密：

public void onClick(View arg0) {

    sp=this.getSharedPreferences("AccessApp", MODE_WORLD_READABLE); 

    byte[] key = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5 };

    try {
         String decryptedUser = decrypt(user, key);  
         user = sp.getString("USERNAME_KEY", decryptedUser);
    }
 catch (Exception e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}   
try {
         String decryptedPass = decrypt(pass, key);  
         pass = sp.getString("PASSWORD_KEY", decryptedPass);

} catch (Exception e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

   if(lBttn.equals(arg0)){

      if((uname.getText().toString().equals(user))&& 
        (pword.getText().toString().equals(pass)))

            {
          Toast.makeText(this, "You are Logged In", 20000).show();

               Intent intent;
               intent=new Intent(this,details.class);
               startActivity(intent);
              flag=1;
            }

        else 
           {
            Toast.makeText(this, "Wrong Username or Password",20000).show();
            flag=0;   
           }       
        } 
        else if(cBttn==arg0){
            AlertDialog.Builder builder=new AlertDialog.Builder(this);
          builder.setTitle("Exit");
         builder.setMessage("Do you want to exit");
    builder.setCancelable(false);
    builder.setPositiveButton("Yes",new DialogInterface.OnClickListener() {

   public void onClick(DialogInterface dialog, int which) {
   // TODO Auto-generated method stub
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_HOME);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);

  finish();
   }
  });
    builder.setNegativeButton("No", new DialogInterface.OnClickListener() {

            public void onClick(DialogInterface arg0, int arg1) {
               arg0.cancel();
            }
        });
    AlertDialog alert=builder.create();
    alert.show();

        }

    }
@Override
public boolean onKeyDown(int keyCode, KeyEvent event)  {
 if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {

     Intent intent = new Intent(Intent.ACTION_MAIN);
        intent.addCategory(Intent.CATEGORY_HOME);
        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        startActivity(intent);
     finish();
 }
 return super.onKeyDown(keyCode, event);
 }

public static String decrypt(String encryptedText, byte[ ] key) throws Exception {
    SecretKeySpec skeySpec = new SecretKeySpec(key, "AES");
    Cipher cipher = Cipher.getInstance("AES");
    cipher.init(Cipher.DECRYPT_MODE, skeySpec);
    byte[] toDecrypt = Base64.decode(encryptedText);
    byte[] encrypted = cipher.doFinal(toDecrypt);
    return new String(encrypted);
 }
 }

声明：

public class AccessApp extends Activity implements OnClickListener {
private SharedPreferences sp;
String user,pass;
Button lBttn,cBttn;
EditText uname,pword;
Intent i;
int flag=0;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{ 
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    lBttn=(Button)findViewById(R.id.login_button);
    cBttn=(Button)findViewById(R.id.cancel_button);
    uname=(EditText)findViewById(R.id.username);
    pword=(EditText)findViewById(R.id.password);

    lBttn.setOnClickListener(this);
    cBttn.setOnClickListener(this);
}

Answer 1

对不起。我正在改变我的答案。我之前说过的是完全错误的。
你得到错误的原因

java.lang.NullPointerException: Input string was null.

是因为你宣布了

String user;

您尚未初始化它并且正在调用

String decryptedUser = decrypt(user, key);

现在在函数decrypt中，用户为空。

输入字符串为null Base64解码

1 个答案: