Abstract: A method of preventing removal of a smart card having a counter zone associated with a first reference zone, and a balance zone associated with a second reference zone. The counter zone has at least two levels of counters, each having at least two bits. The counter zone is operable in accordance with the abacus principle. The first reference zone has at least one register with at least two bits and is operable to display the proper erasing of the counters. The second reference zone has at least two fields. Bits of a balance are written simultaneously in the balance zone and in the second reference zone. The balance zone and the second reference zone each include one validation bit making it possible to know if the balance is fully written.

Abstract: A smart card having a counter zone associated with a first reference zone, and a balance zone associated with a second reference zone. The counter zone has at least two levels of counters, each having at least two bits. The counter zone is operable in accordance with the abacus principle. The first reference zone has at least one register with at least two bits and is operable to display the proper erasing of the counters. The second reference zone has at least two fields. Bits of a balance are written simultaneously in the balance zone and in the second reference zone. The balance zone and the second reference zone each include one validation bit making it possible to know if the balance is fully written.

Abstract: The protection of the transfer of data between a videotex terminal (TVX) and a server (SE) is carried out by means of an additional package (BA) connected to a video adaptor connector (PPI) of the terminal (TVX). In a presession embodiment, the package acts on the switching device (AIG) of the terminal by monitoring any other action on said switching equipment. The switching cabinet and the server conduct dialogue according to a predetermined sequence of operations comprising the definition of a transmitted session key encrypted in accordance with a basic key. Any anomaly occuring during this dialogue aborts the presession mode.