Emulate DESFire card on NFC phone

Question

For my master thesis I'm investigating the possibility to use an NFC enabled phone for opening off-line door locks. These locks currently work with DESFire cards which contains authorisation data. Furthermore, the card is also used to update configurations and obtain maintenance messages to/from the lock. The goal is to update and read this information to/from the lock via an application on the phone that communicates with an external server over the internet ultimately making the exchange of this information more efficient.

Currently, I think the best choice for getting card emulation to work is to use an SD card with NFC and a secure element. This provides two possibilities:

1) A possibility is to implement a custom made java card applet that emulates a DESFire card. Theoretically, this should be feasible as DESFire cards optionally supports APDUs (ISO7816).

2) Some of the NFC SD cards available on the market offer DESFire emulation as a ROM.

I've the following questions:

• For option 1 I wonder what will happen if the off-line lock / reader initiates communication using DESFire 'native' commands instead of APDUs. Is it possible to interpret non-APDU commands from java card? If not, it probably means it will not work?

• Is it possible to manage the content of an emulated DESFire card in option 2? The NFC SD cards that I saw provides a proprietary API to access the secure element. It allows this by transceiving APDUs. The emulated DESFire, however, is not a java card applet in this case but it is a ROM which may or may not support this communication with APDUs.

I know this question is not strictly related to programming. But I found that there are quite some people on stackoverflow with expertise on NFC related topics. In fact, I found most of my information here.

Thanks

Answer 1

In order to answer 1 you would need to examine carefully ETSI 102 705 and see if the API lets you process CLT events (lower level protocol exchanges) instead of the contactless chip. I think this is unlikely.

In option 2 there surely is a way to manage the contents, otherwise the proposed desfire emulation would be totally worthless, but this might end up being partly proprietary, or requiring a substantial effort in cryptography, in which case you need to obtain the right keys.

All in all, if I were you, I would do ISO7816 (14443-4) card emulation using javacard, and forget about all the NXP proprietary stuff, which is built to make you buy licenses and associated software solutions.