Is it possible to make data usable after reading it with NFC

Question

Hi a question got stuck in my mind.. When I tap my Oyster card(a card you use for public transportation in London)back of my Android mobile phone that has NFC feature, I can display the remaining balance with an App. It means that the data could be read through NFC. After reading the data is it possible to make it usable? I mean rather than tapping the card itself in toll gates, Cant we just tap the NFC enabled phone to go through the gate?How can it transferred to a data that makes phone to behave like an Oyster card? Think like tap and pay in some stores..

Answer 1

Your idea is technically feasible (many companies are building similar systems now) but quite complex to implement, because you need to collaborate with different organizations.

First, you would need to emulate the entire Oyster card in the phone (the guide linked by Xaver Kapeller in the comments is a great place to start). Since the Oyster card is not built on a plain NFC JavaCard, but on Mifare DESFire (a technology owned by NXP), very probably you would need NXP's permission.

Second, you would need to work together with TfL (Transport for London) so that they (or anyone working on their behalf) copy the data in the Oyster card onto the app emulating the Oyster card, either on a Secure Element on the phone itself or on a server, if you are using HCE. That "data" is not just the remaining balance you can read with an App, it is also a number of keys and other information that are checked by the readers on buses or on the Underground turnstiles to verify that the ticket is legit.

A good answer would need to be quite long, I hope this is enough to point in the right direction... You can read a recent piece of news here.