Contactless bank cards

Peter Tomlinson pwt at
Thu Nov 18 08:20:25 GMT 2010

Roland Perry wrote:
> In article <B33B3C603B7644689B64664F1D049B3E at your41b8d18ede>, Tom 
> Thomson or was it Michael? <colinthomson1 at> writes
>>> I've never actually found a machine to try my card out upon. But the
>>> Oyster pads in London require the card to be pretty much out of a 
>>> wallet
>>> and touching the surface. Similarly the RFID cards used on the buses in
>>> Nottingham. The technology is dozens of order of magnitude away from
>>> scanning the bus pass in the passenger's pocket as he gets on board.
>>> -- 
>>> Roland Perry
>> Well Roland, I usually understand "orders of magnitude" as decimal 
>> ones,  But even if I were to assume that you meant binary orders of 
>> magnitude (which would usually suggest to me an intention to mislead, 
>> but let us assume that although you meant binary you had no such 
>> intention) "dozens" means a factor of at least 2 to the 24th, or 
>> something a bit bigger that 2 times 10 to the 7. If I guess that 
>> there's an inverse square law in there somewhere,
> Apparently it's an inverse 4th power, and the Nottingham bus passes 
> have to be held pretty much *on* the reader[1] - no more than a 
> millimetre of air gap is acceptable.
> [1] Which is quite tiresome when you have several senior citizens 
> boarding, who seem to find the technology difficult, and it takes a 
> while for them to position their cards exactly right.
Not all bus ticket machines are the same. I'm fairly certain that the 
Nottingham bus machines will soon be replaced.


More information about the ukcrypto mailing list