Abstract: To avoid the need for making microprocessor-fitted bank cards which, although they cost little, are in a relatively far too expensive range, money cards with only memory zones are made. They then have four memory zones, one zone pertaining to the identity of the bearer or to that of the card, one zone pertaining to the financial balance, a third zone pertaining to an interaction counter. This interaction counter counts the number of financial operations performed with the card. A fourth zone includes a certificate. This certificate is prepared, in each reader that performs a transaction with the card, with a DES algorithm. The value of this certificate is a function, according to an algorithm common to all the readers, of the identity, the content of the interaction counter and the balance. When a new operation is performed with the card, it is ascertained beforehand that the content of the certificate is the same as the one that can be recomputed by any terminal provided with the same algorithm.