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Process for exchange of rights between microprocessor cards

  • US 5,247,578 A
  • Filed: 01/22/1992
  • Issued: 09/21/1993
  • Est. Priority Date: 01/22/1991
  • Status: Expired due to Term
First Claim
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1. Process for exchange of rights between microprocessor cards consisting in debiting a first card (A) by a certain amount (M) and in crediting a second card (B) by this same amount (M), wherein:

  • cards (A) and (B) are identified by identities, respectively (a) and (b),card (B) to be credited identifies itself to card (A) to be debited by sending its identity (b) and a number (N) that it has selected to card (B) and card (B) indicates an amount (M) of the rights to be exchanged,card (A) to be debited verifies if its balance of rights is at least equal to requested amount (M),in the affirmative, card (A) to be debited reduces its balance of amount (M) and calculates a voucher, which is a function F of amount (M), of identify (b) of card (B) to be credited and of number (N), or F(M,b,N),card (A) to be debited sends this voucher F(M,b,N) to card (B) to be credited,card (B) to be credited receives this voucher F(M,b,N), and deducts from it amount (M), identity (b) and number (N),card (B) to be credited verifies if calculated amount (M) is indeed the requested amount (M), if the calculated identity (b) is indeed its own and if the calculated number (N) is indeed number (N) that it had selected,in the affirmative, card (B) to be credited changes number (N) for the next exchange and exchanges its balance of amount (M) in question, this process comprising using the function F to calculate voucher C, as defined and used by the following operations;

    defining in advance multiple ciphering keys (K1, K2, . . . , Km, . . . , Kn, . . . ),storing in card (B) to be credited one of these multiple keys, or (Kn), where key number n is a function (u) of identity (b) of card (B), (u(b)=n),storing in card (A) to be debited certain varied keys Ka1, Ka2, . . . , Kan, . . . which are each a function of multiple keys K1, K2, . . . and of identity (a) of card (A) to be debited, these varied keys being loaded in card (A) during its customization,having card (A) to be debited receive identity (b) of card (B) to be credited and calculate row n of the varied key by function u(b) and deduct from it that of varied keys Kan with which it is to calculate voucher (C),having card (B) to be credited calculate varied key Kan which was used in the calculation of the voucher that it received and this with its own key (Kn) and with identity (a) corresponding to card (A) to be debited, card (B) to be credited then being able to decipher voucher C with this varied key Kan.

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