Get the data payload of a tag

Question

I have some card which uses NFC (e.g. a student ID card or a debit card). These cards don't use NDEF for store data. How can I get the payloads of these cards?

Currently, I use this code:

if (intent.getAction() != null && NfcAdapter.ACTION_TECH_DISCOVERED.equals(intent.getAction()))
{
    Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
}

Can anyone spot how can I get the payload of the tag?

The card's technologies are android.nfc.tech.IsoDep and android.nfc.tech.NfcA.

Answer 1

You could get NfcA object as this:

Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
NfcA nfcA = NfcA.get(tag);

After you could communicate with tag by sending APDU's as this:

byte[] apdu = [...];
byte response = nfcA.transceive(apdu);

Answer 2

Getting the payload from a non-NDEF tag/smartcard heavily depends on what type of tag you use. Tags/smartcards can range from being simple data storages using a flat, linear memory structure, over data storages using a file-system based memory structure, to processor smartcard containing executable program code and data.

In your case, the tag is based on NfcA + IsoDep technologies (i.e. it implements the transport protocol as standardized in ISO/IEC 14443-4 Type A). Therefore it's unlikely that your tag belongs to the group of simple linear-addressable memory tags. Instead, it is more likely (though not necessarily true) that your tag implements some communication protocol and possibly some file-system like structures as standardized in ISO/IEC 7816-4.

Anyways, you need to find out/know and implement the protocol that the tag speaks in order to retrieve any data from it. If your "tag" is a payment card, this might be specified in the EMV Contactless Specifications for Payment Systems. If your tag is a passport, this is specified in ICAO 9303.

• If your tag is a memory tag with flat memory layout, it will typically have simple read commands that take an address offset and a length as parameters. In addition, there may be access control mechanisms that require you to provide proof of knowledge of a key/password.

• If your tag is a memory tag with file-system based memory layout, it will typically have commands for selection and access of files. This may be based on ISO/IEC 7816-4. In addition, there may be access control mechanisms that require you to provide proof of knowledge of a key/password.

• If your tag is a processor smartcard, you typically can't just read the whole data memory. The program code executed on the card will decide, which information is accessible under which conditions. For instance, private keys are usually designed in a way that they can never leave the card. E.g. EMV payment cards fall into this category.