Transaction data stored on Contactless Credit Cards

Peter Tomlinson pwt at
Tue Sep 9 22:06:52 BST 2014

An ITSO transaction very often involves both read and write to the card, 
particularly when you have pre-purchased a ticket and the gate has to 
mark it as 'in use'. ITSO reads the entire ticket, checks its signature, 
writes back if necessary. ITSO terminals have a SAM.


On 09/09/2014 21:28, Roland Perry wrote:
> What I think I know from reading ITSO specifications is that in order 
> for the contactless transaction to take place in the sub-second window 
> that travellers expect there isn't time to *both* read the card's 
> credentials *and* write any kind of transaction data *back* to the card.

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