Hide an NDEF record into the NDEF Message?

Question

I have developped 2 Android applications. The first one, to write into an NFC tag, and the second to read the contents I have written .

This is what i did in the first application (WriteNFC)

private NdefRecord createRecord1(String data)
{ 
byte[] payload = data.getBytes(Charset.forName("UTF-8"));
byte[] empty = new byte[] {};
return new NdefRecord(NdefRecord.TNF_ABSOLUTE_URI, empty, empty, payload);
}
private NdefRecord createRecord2(String data)
{ 
byte[] payload = data.getBytes(Charset.forName("UTF-8"));
byte[] empty = new byte[] {};
return new NdefRecord(NdefRecord.TNF_ABSOLUTE_URI, payload, empty, empty);
}

And in the second application (ReadNFC)

NdefRecord cardRecord = msg.getRecords()[1];//Extract the second Record
String url_data = new String(cardRecord.getType());//Read data type

When I read with my own application (ReadNFC), of course I had on screen only the payload of the second Record, which I stored through "Record Type". But with a third-party application, especially that natively installed ("tag") -shown in photo-, It display correctly the first record, and for the second it's an empty field. How can I hide this field. Otherwise, how can I force the other third-party applications to not read the second record?

Answer 1

You simply cannot do that. Android will read the complete NDEF messages (i.e. all records) and pass it on in the Intent to an app.

Answer 2

Upps, it is no wonder this is happening, look at your code. First

return new NdefRecord(NdefRecord.TNF_ABSOLUTE_URI, empty, empty, payload);

then

return new NdefRecord(NdefRecord.TNF_ABSOLUTE_URI, payload, empty, empty);

So the 3rd party apps are really showing the correct data, you have a bug in your record creation.

The native NDEF support in android is somewhat crude (byte-array based), so I've written a library which helps in creating records - which you might find interesting. The above issue might be simple to resolve, but there are many other much more complex record types, so some help might come in handy ;-)

Edit: So if this is the preferred result, rather create an Unknown Record and put your 'secret' data as the payload - the will not be any good way for any 3rd party app to display that data - whereas the ID of the absolute URI Record certainly can be displayed by any NDEF-reading app (like mine?)

Answer 3

This third party app was bothersome to me, so I had to use foregroundDispatch to read the tag contents manually, there you have the freedom to read or not read anything you want. This snippet is from the OnResume(). `

mNfcAdapter.enableForegroundDispatch(this, pendingIntent,
                intentFiltersArray, techListsArray);

            Toast.makeText(getApplicationContext(), "TAG disscovered",
                    Toast.LENGTH_LONG).show();
            Parcelable[] rawMsgs = getIntent()
            .getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);

            if (rawMsgs != null) {
                NdefMessage[] msgs = new NdefMessage[rawMsgs.length];


                for (int i = 0; i < rawMsgs.length; i++) {

                    msgs[i] = (NdefMessage) rawMsgs[i];
                    setText=new String(msgs[i].getRecords()[0].getPayload());
                }
                mInfoText.setText(setText);
            }

        }`

Here I get payload of the 1st record.