On 06/09/2019 15:58, Andy Burns wrote:
Harry Bloomfield wrote:

Andy Burns wrote:

does the shop till know whether it's talking to a plastic card, or an
iThing?

It must do, otherwise other tills wouldn't know to ignore the £30 limit.

But does the till know that, or does it just present the amount to the
card, and the card or iThing gives a yes/no answer with some sort of
token to prove it?

One presumes the till obtains an identity from the device (apple pay,
contactless card) and uses this id to query the bank. The bank will know
from the id what the device type is, the bank will then send an
authorization (or decline) to the till.