In message , at 22:04:12 on Mon, 17 Dec
2012, Mizter T remarked:
My understanding is that a (very) small amount of data can be written
to an EMV-standard contactless card - i.e. the card itself can prove
that it has been validated (e.g. where and when).

Validated once in its life, after the very first transaction, or after
every one?

The problem with doing it for every transaction is that the card is
allowed to be removed from the RF field *before* the terminal has even
started its validation sequence.
--
Roland Perry