• Gaduc
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Topic: A dynamic NFC tag does it exist?

I'm looking for a dynamic NFC tag that is able to dynamically change its content or a NFC tag that is able to talk SNEP.
Don't answer "a smartphone", that's not my target.
My target is to offer a simple way of authentifying someone that doesn't have a NFC handset (because it's expensive or because the battery is empty, etc).

The idea is to use the NDEFormat to exchange data based on a challenge sent by an initiator (the reader that stands in the wall near the door).
The tag then computes a NDEF with a specific field (to be defined) whose content is a result of a cryptographic function applied to the challenge (nothing new here: windows, Kerberos, etc have been working this way for a couple of years).

The reader then reads this NDEF and applies the same cryptographic function to its challenge: if they match the door opens else the door keeps closed.


db

  • Registered: 2009-10-07
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Re: A dynamic NFC tag does it exist?

Have a look at http://blog.felicalauncher.com/en/?cat=6, I think that's what you're looking for.

3 Reply by Gaduc (edited by Gaduc 2012-04-27 04:01:01)

  • Gaduc
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Re: A dynamic NFC tag does it exist?

nephets wrote:

Have a look at http://blog.felicalauncher.com/en/?cat=6, I think that's what you're looking for.

Yes, thx to point this ou.
But, despite the fact that this tag is well documented and publicly available it's not very autonomous as well as not very wearable: I doubt that anybody would want to use it daily with an Arduino in the pocket.t
The idea is there but with the CPU inside the chip not outside!
I'm looking for a product not for something experimental.

Thx again!
db

  • yobibe
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Re: A dynamic NFC tag does it exist?

If you look for a product the only thing I can think of is to take a Javacard and write your own applet to emulate a Tag4.
But reading a NFC tag does not send much info *to* the tag so I don't know how you will send your challenge to the tag while respecting the standard procedure to read a Tag4. Writing a NDEF then reading it back?

Phil

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  • Gaduc
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Re: A dynamic NFC tag does it exist?

yobibe wrote:

If you look for a product the only thing I can think of is to take a Javacard and write your own applet to emulate a Tag4.
But reading a NFC tag does not send much info *to* the tag so I don't know how you will send your challenge to the tag while respecting the standard procedure to read a Tag4. Writing a NDEF then reading it back?

Phil

Maybe the trick is there: writing a Java applet (*) for a Javacard not to emulate a type 4 tag (**) but to talk SNEP.

But do you think it's possible for a smart card (that is to say for something that is remote powered and not self powered) to become a peer? Don't you thing that's something in the lower layers (ISO 14443-1/2/3) that could forbid such a card to establish a P2P dialog?
The Felica which nephets talked about is self-powered (by the Arduino for example).

Regards,

db

(*) Starting from the MUSCLE applet maybe.

(**) Because, as you said it, it's not possible for a tag, following the specification, to know that the initiator sent something to it as well as the initiator is not expected to send something during this kind of dialog.

  • yobibe
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Re: A dynamic NFC tag does it exist?

I didn't say it wasn't possible for you to emulate a tag4, I said you've also to think also on how to send data to the smart tag.
One way can be to "write" some content into the NDEF file (see NDEF update in the tag4 spec) and "read" back that same NDEF file.
Up to the Java applet to interpret those APDUs to interface with your challenge/response protocol.

Now about implementing SNEP on a Javacard...
SNEP works on top of LLCP while Javacard communication is APDU-based, I don't know LLCP enough but I think it's quite incompatible.

So first option is still your best bet.

yobibe's Website

7 Reply by Gaduc (edited by Gaduc 2012-05-01 09:50:45)

  • Gaduc
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Re: A dynamic NFC tag does it exist?

yobibe wrote:

I didn't say it wasn't possible for you to emulate a tag4, I said you've also to think also on how to send data to the smart tag.
One way can be to "write" some content into the NDEF file (see NDEF update in the tag4 spec) and "read" back that same NDEF file.
Up to the Java applet to interpret those APDUs to interface with your challenge/response protocol.

Now about implementing SNEP on a Javacard...
SNEP works on top of LLCP while Javacard communication is APDU-based, I don't know LLCP enough but I think it's quite incompatible.

So first option is still your best bet.

Sheat, I forgot Javacard were based on APDU!

NDEF was a way to work while following the NFC Forum specs. But, in fact, it seems to be far more complicated that using the old way: a good old APDU with arguments.

That is: sending an specially forged APDU that means: take this argument as a challenge and prepare an answer with the response about which I'll ask for in a few milliseconds.
Ok, that's proprietary but no more that something that could modify a NDEF.

What do you think?

db

Edit: APDU as the only communication mode was true for earlier and actual classic edition of Javacard. That's not true anymore for Javacard Connected Edition that appeared with Javacard 3.0. The connected Edition which is more like J2ME (the Java version for mobile equipment) can talk HTTP and  HTTPS and, therefore, TCP/IP.
There could be something to dig in there.
Problem 1: there seems there's no commercial product compliant with JC3 CEdition at this time.
Problem 2: according to the stack figured in the specs, ISO/IEC 14443 is used only with APDU.