[Issuedrinks] [Fwd: Re: Fwd: rfid]

Bjorn Wijers bjorn at waag.org
Thu Aug 10 06:58:34 UTC 2006

Interessant. Het is dus niet zo simpel als we dachten.

Blijft het opmerkelijk om te zien dat deze Harald zijn werk wel onder 
een open systeem doet (GPL/CC), terwijl hij geen 'publieke' functie 
vertegenwoordigt en de prof die mijns inziens wel een publiek functie 
vertegenwoordigt niet. Of is dit onzin?

Koen Martens wrote:
> Sprak (mailde..) er met iemand die ik ken (Harald Welte, aka
> LaForge, van ccc o.a.) over, en die had nog wel wat interresante
> opmerkingen (geforward met permissie):
> -------- Original Message --------
>> I was talking to enno in irc today, about the rfid guardian
>> (http://www.rfidguardian.org/).
>> They don't seem to publish any schematics or anything, but i thought
>> such an appliance would be actually quite simple to build. RFID is
>> basically a binary search + some serial protocol, so i guess a
>> simpel pic with some rudimentary send/receive circuit ought to be
>> enough.
> I disagree.  It's not at all "quite simple".  A number of factors you
> (and I guess also the rfidguardian people to a certain degree) forget to
> take into consideration:
> 1) RFID is not one standard/prtocol.  There are half a dozen different
>    publicly documented standard (ISO 14443-1,2,3,4, ISO 15693,
>    ISO18000-6, ... ) and a number of vendor-specific proprietary systems
>    such as mifare, legic, etc. for which very little to no information
>    is known.  some of those systems use binary search, but they all use
>    different modulation / framing / clocking / frequency / etc.
> 2) Many commonly found applications (ePassport, electronic public
>    transport ticketing, ... use encryption, so any man in the middle
>    'monitoring and regulating use' will be impossible.
> 3) the magnetic coupling based systems have extremely short range, and
>    the reader-transponder vs. transponder-reader signals are at least
>    60dB apart (dynamic range problem).
>> Anyway, enno thought you might already be working on something like
>> that, so i thought i'd just send you an email. I'm interrested in
>> stuff like this, that's my motivation :)
> Milosch (see Cc) and I have just finished a free (GPL licensed firmware,
> CC-sharealike-attribution schematics, ..) RFID reader design that can be
> used for mainly ISO 14443 and 15693 but probably other 13.56MHz based
> systems.  We're also working (contract based) on a 14443 PICC
> (transponder-side) emulator, which will probably be released at some
> point in september, also under GPL/CC licenses.
> There are many issues that need to be looked into, stuff like
> reconfigurable higher-order analoge filters, and that's only for
> supporting all bitrates of only ISO 14443.  Our devices will run on a
> Atmel AT91SAM7 (ARM7TDMI cpu) controller running at 48MHz clock, not a
> small PIC ;)
> So if you want to get into implementing any such device, please don't
> make the error of underestimating the amount of work required.
> And we're just talking about the 'usual' reader and card interface, not
> about actively jamming signals (which would have to be bit clock and
> phase accurate) or anything like that.  In theory this is all possible,
> but actually designing a device that does it is a somewhat different
> task.  Also, it's difficult to jam a _magnetically_ coupled signal over
> distance, since the magnetic field very quickly deterioates with
> distance (compared with the electric field).  But having a simulated tag
> in the field (<10cm) of a 13.56MHz reader would certainly provide and
> ideal opportunity to cause collisions with about every known anti
> collision algorithm :)
> ... and once we're finished with the task for 13.56MHz, EPCglobal /
> ISO18000-6 systems will start to be introduced in supermarkets,
> providing new challenges at handling 860-920MHz signals with backscatter
> modulation....
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Bjorn Wijers
Waag Society / for old and new media
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