Contactless bank cards

Roland Perry lists at
Thu Nov 18 16:06:05 GMT 2010

In article <0EFE4206-66FB-444F-89E7-6ACC006B0194 at>, Ian 
Batten <igb at> writes
>> If we want to put this into perspective with some real world results there's a paper here <
>>usenix06/index.html> where a reading range of 25 cm was achieved with USD 110 worth of hardware. This paper is 4 years old and may not even
>>represent the state of the art at the time.
>Perhaps not.  But did you notice the slight flaw in using this surreptitiously?  It's in section 2.4:  ``A necessary condition for an increased
>range is a larger antenna. Theoretical analysis ([Lee03]) shows that for a desired range, r, the optimal antenna diameter is
> r. We wanted to demonstrate a reading range of 25-30 cm.''
>They used a 39cm diameter copper tube loop to get 25cm.

They also say that 35cm is as far as they think its possible to get 
(others they cite say 40-50cm, but it looks like 40cm requires 4amps at 
12 volts). And also:

"We are about half-way toward a full-blown implementation of a 
relay-attack."  Four years on... did they ever get there?

And the power supply required is a battery the size and weight of a 
brick (they only mention that it's easy to source) and isn't included in 
the $100 cost. (They are about £35 each).

So it's probably more evidence that the theory's fine, but I do feel it 
proves the point I originally made (and which has attracted some 

I'm also not inclined to think that the solution is susceptible to 
Moores Law, more likely to "Fusion Power Law", which is basically that 
if the physics is that difficult, you'll constantly be living in hope, 
but a few years away from a prototype that's actually useful.
Roland Perry

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