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Abstract

Method for modifying data in a card transaction system including a smart card and a reader capable of reading the card, the card including a non-volatile, erasable and rewritable memory having at least one location to record a data value relating to card transactions. Each transaction results in modification of the data value, the latter being a monotonic function in time. At each transaction, a data value writing operation performs the writing of the new data value (Y) in a first location (B) of two predefined locations in the memory forming a counter, the writing operation erasing the old data value recorded in the second location (A) such that, at the end of the correctly performed writing operation, the first location contains the new data value whilst the second location contains the value zero.

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First Claim