The electronic purse [prepayment cards]

A prepayment card is usually the size and shape of a credit card and has value encoded on it, which is partially used for each purchase until none is left. The card is then normally thrown away, although a growing minority of prepayment cards are designed to be recharged and used again. Prepayment cards usually need some electronic device at the point of sale to carry out the decrementing, and a reloading facility requires other equipment that accepts banknotes, credit or debit cards to put value on the card. So far, payphones and `stored-value tickets' for trains and buses are the largest applications. The author describes the technology involved in magnetic stripe, optical and chip cards. The author discusses the security features of each type of card