[Hackrf-dev] Help with NFC decoding.

[evilsocket]

Yeah as long as I know, NFC-A is modulated on ASK 100% from the reader side
and ASK 10% from the tag side, so using only one type of demodulation I
should be able to see only the reader data and wrongly demodulated tag data
... but once I'll be able to correctly demodulate the reader side, I'll
"follow" the protocol and know what should be demodulated how ....
hopefully :P

I'm pretty sure it's ISO14443a, at least that's what the nfc reader app I'm
using is saying.

2015-04-18 17:46 GMT+03:00 Martin Holst Swende <martin at swende.se>:

> On 2015-04-18 16:10, evilsocket wrote:
> >> I think this is a great goal, but have you considered using GNU Radio
> >> to confirm that it works and then rewrite it in C/C++ piece by piece?
> >
> > Yep but in that case would be copying, not understanding, wouldn't it? :D
> >
> >> Have you looked at the waveform to see if you can identify where the
> >> data is being transmitted?
> >
> > Yep, I'm on the right frequency and it's clearly ASK.
> >
> >> I think you're on the right track.
> >
> > Great! :D
>
> One thing that will bite you with this approach, is that you'll only get
> reader-side of the comms this way. The reader does OOK, but the tag does
> not transmit; it modulates the reader signal. So, depending on whether
> the tag coil is open or closed, it will dampen or not dampen the
> reader-signal. So you'll need to have some more levels to discern these
> pretty small variations in the signal.
>
>
> >
> >> It probably depends on what is being transferred.  A good place to
> >> start would be these specs:
> >> http://members.nfc-forum.org/specs/spec_list/
> >
> > Thanks so much :)
>
> Obviously, depending on what you're observing, it will vary, but I would
> guess that the traffic you're seeing is iso14443a, afaik the most
> commonly used. The documents you're looking for would be the ISO 14443a
> specs. There are four of them:
>
> 1. Physical characteristics
> 2. Radio frequency power and signal interface
> 3. Initialization and anticollision
> 4. Transmission protocol.
>
> Start with 2, and work your way up... I can email them to you off-list
> if you'd like, shoot me an email in that case.
>
> Otherwise, it's probably iso15693 you're seeing. That's more common in
> vicinity (as opposed to "proximity") cards which can be read over a
> greater distance, e.g. ski passes.
>
> Good luck
> /Martin
>



-- 



_________________________
Simone '*evilsocket*' Margaritelli
http://www.evilsocket.net/  <http://www.evilsocket.net/>
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