A portable data or information carrier in the form of a card or the like. In order to maximize the confidentiality of information stored in the carrier, and more specifically to limit the amount of information available to a would-be defrauder monitoring data lines connecting the data carrier to external devices, the data carrier includes a microprocessor and a memory operatively associated with the microprocessor. The memory has three particular zones, namely: (1) a secret zone in which reading and writing operations only by internal circuits of the data carrier are permitted; (2) a working zone in which any reading or writing operations are permitted; and (3) a read zone where only reading operations are permitted. The secret zone of the memory includes at least one key or code which is compared to a key received from a device external to the data carrier to determine whether a particular operation is authorized. To ensure that the data carrier consumes the same amount of current whether the requested operation is authorized or unauthorized, a bit is stored in the memory in either event. In general, the internal handling of data by the data carrier deprives a would-be defrauder of any opportunity to learn the nature of information required to use the data carrier.