Re: Disabling RFID by mains force

[Stefek Zaba <[EMAIL PROTECTED]>]

On Fri, Oct 31, 2003 at 10:11:52AM -0000, Brian Gladman wrote:
> 
> ... I did not answer because this is very dependent on the technical design
> of the RFIDs in question.
> 
> If anyone can point again at any openly available information on the
> _designs_ used in such devices, I will endeavour to take a look at the
> issue.
> 
I've not found a single comprehensive source, but the gubbins over at
www.rfid.org and www.autoid.org may be a start at identifying the
frequencies and read distances. I use the plural as there are multiple
standards in use and proposed, and will continue to be: "RFID" gets used
as a blanket term to cover everything from battery-powered active
transmitters down at 13MHz or therebouts, up to the consumer-oriented
"speak when you're spoken to" tags up at 900MHz or (I think) 2.4GHz. 

A practical design might have two stages - one to locate the tag, by
putting out the standard reading signal (and lighting up some LEDs to
indicate which direction to move the zapper), and then a different
button to push to fire a more concentrated burst of RF to destroy the
ability of the tag to talk back (and verify that it no longer responded ;-)
The higher energy needed for that zapping pulse would be made the
more feasible by being close to the tag, as well as having a few seconds
to charge up the relevant capacitor before releasing all in one glorious
Zap ;-)

Which in turn suggests the countermeasure for the "anti-zap" tag, doesn't
it: when it detects a high-energy RF pulse, simple "spark-gap" arrangements
dissipate the pulse harmlessly, and the tag "plays dead" for the next
<time-period-chosen-for-application>; and when it comes back to life
it's changed its ID, and has set the "tamper" bit.

Ain't ECM, and counter-ECM, and counter-counter-..., fun...

Stefek