How does a mobile driving licence use NFC?
Usually as the handshake rather than the whole conversation. The standard behind mobile licences lets a phone and a verifier set up a channel with a code or a tap, then carry the exchange over Bluetooth, NFC or Wi-Fi Aware, so a tap often starts the transaction rather than being it.
What the standard specifies
The European architecture and reference framework describes what ISO/IEC 18013-5 covers: message structures and transaction flows for requesting and presenting attestations, proximity interface specifications that let a wallet and a verifier set up a communication channel using a QR code or NFC and then communicate over Bluetooth Low Energy, NFC or Wi-Fi Aware, and security mechanisms covering confidentiality, authenticity and the authentication of the verifier.
The same document notes that although the standard nominally specifies the mobile driving licence, those aspects are generic and can be used for any type of attestation. A licence is the first passenger rather than the destination.
A companion standard, ISO/IEC 18013-7, carries the same request and response messages in remote transactions, which is the case where nobody is standing in front of anybody.
Why not do all of it over NFC
Because the two jobs are different. Engagement has to be unambiguous: this phone, that reader, chosen by a deliberate gesture rather than by picking a device from a list, which is the property the no pairing page describes.
The exchange that follows carries a signed data set with a portrait in it, and it works better over a link that tolerates the phone being held in a hand, moved, or turned towards its owner to approve the request.
NFC remains an option for the exchange itself, and the standard allows it. What it gives up is the ability to keep talking once the phone leaves the reader.
What the verifier has to do
Authenticate itself. The framework lists verifier authentication among the security mechanisms, and a wallet is entitled to know who is asking before anything is presented.
Ask for specific elements rather than for the document, because the request is what determines what the holder is invited to approve.
Run on something. Apple documents a mobile document reader for this on the phone itself, prepared with a reader token generated by the verifier's server so the wallet can display the verifier's name and logo during the read, which is the same idea the framework states in protocol terms.
What changes for the holder
The phone stays in your hand. A plastic licence is handed over and read entirely; a mobile one answers a request you approve, and the difference is visible on screen before anything leaves the device.
The request can also be for display rather than for data: a verifier can ask for elements to be shown on screen for visual inspection instead of being returned to an application, which the age page takes up, since that distinction decides what a bar keeps about a customer.
And none of it works where the verifier has no reader. A mobile licence is only as available as the equipment in front of it, which is why the plastic stays in a pocket for a long time yet.
Frequently asked questions
Is the whole licence sent over NFC?
Not usually. The tap or a code sets up the channel, and the exchange runs over Bluetooth, NFC or Wi-Fi Aware, depending on what both ends support.
Do I hand my phone to the verifier?
No. The point of the arrangement is that the phone stays with you and answers a request you approve.
Is this only for driving licences?
No. The framework notes the mechanisms are generic and apply to any attestation, which is why the same standard underpins other credentials.
What if the verifier has no reader?
Then the mobile licence cannot be presented at all. Availability is decided by the equipment in front of you rather than by the phone.