Getting Null Object Reference when Trying to Access Dynamic Data - Android Studio

Question

I'm using it to decrypt a password (said password is in a URI is in another class). If I hardcode the key, it works. I'm trying a dynamic approach, and this is where I struggle due to my lack of experience. I'm not able to get the two classes to work together.

public class Decrypt {

 
    public void myMethod(Context context) {
        try {
            context.getContentResolver().openInputStream(targURI);
        } catch (FileNotFoundException e1) {
                Toast.makeText(context.getApplicationContext(), "Could not read the content. Please check the URI is correct", Toast.LENGTH_LONG).show();
                return;
            }
            BufferedReader reader1 = new BufferedReader(new InputStreamReader(content));
            StringBuffer buffer = new StringBuffer();
            try {

                while ((line = reader1.readLine()) != null) {
                    md5key = md5key + line;
                }
                index = md5key.indexOf("\"MD5_PIN\"");
                md5key = md5key.substring(index + 10, index + 42);
                Log.i("Test:  ", md5key);
            } catch (IOException e1) {
                e1.printStackTrace();
            }
        }

//Decrypts password
    public String encryppass(String pass) {
        return this.decrypt(pass);
    }

    private String decrypt(String paramString) {
        byte[] arrayOfByte = Base64.decode(paramString.getBytes(), 0);
        try {
            this.cipher = Cipher.getInstance("AES");
            this.cipher.init(2, this.keySpec);
            String str = new String(this.cipher.doFinal(arrayOfByte), "UTF-8");
            return str;
        }
        catch (Exception exception) {
            exception.printStackTrace();
            return null;
        }
    }
}

MainActivity:

    @Override
    public void onClick(View view) {

        switch (view.getId()) {

            case R.id.exploit1:
                String[] arrayOfString = {"name", "pwd"};
                Cursor cursor = getContentResolver().query(
                        Uri.parse(PWDMANAGER_URI), arrayOfString, null, null, null);

                Decrypt pp = new Decrypt();
                try {
                    if (cursor.moveToFirst()) {
                        do {
                            String name = cursor.getString(0);
                            String encrypted = cursor.getString(1);
                            String decrypted1 = pp.encryppass(encrypted);
                            Log.i("Title:     ", name);
                            Log.i("Password:  ", decrypted1);
                        } while (cursor.moveToNext());
                    }
                } catch (NullPointerException exception) {
                    exception.printStackTrace();
                }

   

Any suggestions on how to get these classes working together?

Answer 1

What you've got is an IllegalArgumentException thrown by the SecretKeySpec constructor, specifically in this line:

SecretKeySpec keySpec = new SecretKeySpec(this.md5key.getBytes(), "AES");

A bit of digging around in the documentation reveals that this exception is thrown

"if algorithm is null or key is null or empty".

In Java, String md5key = ""; is an empty String, thus throwing this exception when passed to the SecretKeySpec Constructor. In order to solve it, initialise your SecretKeySpec after md5key has a proper value. More specifically, change that line to:

SecretKeySpec keySpec;

and add this line where Log.i("Test: ", md5key); is:

keySpec = new SecretKeySpec(this.md5key.getBytes(), "AES");

---

MainActivity:

Before calling encryppass() in this line:

String decrypted1 = pp.encryppass(encrypted);

You'll need to run myMethod(), in order to obtain the md5key value from the xml file. Simply add, before the line mentioned above, the follwing:

pp.myMethod(this);

In this case, this is referring to MainActivity, and is the Context.

---

The following are a few more trivial mistakes (they won't cause any errors, but aren't really in good practice either - or are redundant):

1. There is no need for a second switch with the exact same condition. Just add a second case to the original switch:

    switch(view.getId()){
        case R.id.exploit1:
        //code for exploit 1
        break; //is necessary, since switch is continuous, therefore, it will continue executing until it finds a break. Without it, it will also execute the next case(s)
   
        case R.id.exploit2:
        //code for exploit 2
        break;
    }
   

2. In your database query code, if(cursor.moveToFirst()) is reduntant. The way you did it is also fine, but you could more simply do:

    while(cursor.moveToNext()){
        String name = cursor.getString(0);
        String encrypted = cursor.getString(1);
        String decrypted1 = pp.encryppass(encrypted);
        Log.i("Title:     ", name);
        Log.i("Password:  ", decrypted1);
    }
   

   The first time cursor.moveToNext() is called, it will move to the first position. Because of this, the statement needs to run at least once before the cursor is used so, naturally, this will not work with a do...while() statement.