Importance

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Abstract

A smart card, which in normal use in a network allows the transfer of goods/services to a user of the card from a network operator by subtracting prepaid units of value stored in the card. The card has an embedded integrated circuit with a serial number unique to each card, and a prepaid units register for storing a number of remaining units of prepaid value. In response to an interrogation, the serial number and the number of remaining prepaid units may be read out. A key number is also stored in the circuit. It has a first portion unique for each card, and a second portion which is common to a plurality of cards, but unique for a network operator. The key number in normal use of the card cannot be read from the card. An algorithm is also stored in the card, and in normal use it also is not readable from the card. A microprocessor calculates a certificate in accordance with the algorithm as a function of the key number and the number in said prepaid register, and the certificate is readable from the card.

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First Claim