BBC Moneybox - contactless hiccups

Tony Naggs tony.naggs at
Mon May 20 15:44:03 BST 2013

On 20 May 2013 10:49, Chris Edwards <chris-ukcrypto at> wrote:
> On Mon, 20 May 2013, Roland Perry wrote:
>> What if the contactless credit card is adjacent to an Oyster or ITSO card in
>> your wallet?
> $workplace uses a mifare card based entry system (wave your wallet
> containing card at door reader).  Last year, I started frequently having
> problems opening doors.  Then I realised this was due to my bank having
> issued a new visa card, which has the "pay-by-wave" logo (looks a bit like
> a WiFi symbol).  Removing this visa card from my wallet reinstated by
> ability to open doors.
> I had some idea the protocols specifically catered for multiple cards, and
> that the door card reader would be able to "select" the card it wants to
> talk to.  But if so, this doesn't seem to work very well (for me).

Many door locks simply try to read the unique Id (UID) of a card, &
search for it in an access rights table. The ones I've encountered are
unable to cope with multiple cards presented together.

Credit & debit cards may have random or fixed Ids, and the card
function is identified by further information on the card. If there
are multiple cards a terminal could simply charge the card it
identifies with credit/debit functionality - this may still not be the
expected behaviour.


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