[lcabral]

This uses the same flow as many transportation cards (which in some countries can also be used to purchase goods). Essentially the card chip holds the debit amount it has (the user makes an initial transaction to load it, debiting the money from a debit/credit card or paying for directly with money) so that every time a transaction occurs, the value in card is altered directly. This system also has the potential of making transactions fully anonymous as no-one needs to know who the holder of the card is or where he spends his money.