Re: [Discuss-gnuradio] detecting covert RFID scans

[jean-michel . friedt]

I'll discuss a bit of passive RFID at FOSDEM ... I think there are two
parts to the question: detecting RFID measurement attempts on the one
hand, and decoding the backscattered signal on the other hand. Detecting
RFID is, imho, obvious: because the backscattered signal decays as
1/d^6 for an inductive coupling, and because of the inefficiency of
the rectifier diode when considering silicon based RFID, the emitted
power must be very strong, and making a simple carrier detection of a
10-W emitter is very simple (since the emitted carrier power decays as
1/d^2). Getting the backscattered (amplitude modulated) signal is a
different story, with an efficient signal to noise ratio requiring the
removal of the carrier, which I cannot think of an obvious strategy if
the emitted carrier is not recorded as well for a coherent demodulation.

JM

> On 27/12/15 19:03, Marcus Müller wrote:  
> > The problem is that technically, the energy sent out by an RFID
> > reader isn't big enough to detect readers from afar; they are
> > near-field devices, as opposed to the typical far-field antenna
> > based radio transmitters.
> >     
> 
> If the sniffer was carried in close proximity to the card itself (e.g.
> the card and sniffer in a backpack) and the backpack passed a hidden
> RFID scanner at the entrance to a shop, would the sniffer be able to
> detect the communication?