Storing key using KeyStore in Android

Question

I am using KeyStore to protect my private key but when the line:

FileOutputStream fos = ctx.openFileOutput("bs.keystore", Context.MODE_PRIVATE);

is executed I have this exception:

'java.lang.NullPointerException'.

I don't understand where is the problem.

Code:

    private Context ctx;

    public DataSec(Context ctx) 
    {
    ctx = this.ctx;
    }

    public void genKey() throws Exception
    {
    SecretKey key = KeyGenerator.getInstance("AES").generateKey();

    KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
    ks.load(null, "clavedekey".toCharArray());

    PasswordProtection pass = new PasswordProtection("fedsgjk".toCharArray());
    KeyStore.SecretKeyEntry skEntry = new KeyStore.SecretKeyEntry(key);
    ks.setEntry("secretKeyAlias", skEntry, pass);

    FileOutputStream fos = ctx.openFileOutput("bs.keystore", Context.MODE_PRIVATE);
    ks.store(fos, "clavedekey".toCharArray());
    fos.close();        
    }

Thanks for the Help!

Answer 1

Change:

public DataSec(Context ctx) 
{
ctx = this.ctx;
}

To

public DataSec(Context ctx) 
{
    this.ctx = ctx;
}

Right now, you're assigning the context parameter in the method to the same value as the global one, which is null. Due to this, your context doesn't actually get stored.