Abstract: A process and a device for authenticating the signature of a signed message includes a nominal signature card (1a) coupled to a transmitting device 1 which sends signed messages. The card (1a) includes at least one memory (5) in which there are secretly prerecorded at least one secret key (S) and one program (P) which automatically processes the signature of a message (M), as well as circuits (6) for computing the signature (SG). A control card (3b), which is not nominal, is coupled to a device (3) for receiving signed messages. The card (3b) includes at least one memory in which there are secretly prerecorded at least the secret key (S) and the program (P) for recomputing via processing circuits (15) the signature (SG) of the received message (M).

Abstract: The transmission of signed messages occurs between a transmitter (1) and a receiver (3) connected by a transmission line system (2). The transmitter (1) and the receiver (3) respectively comprise a coding device 7 and a decoding device 11. Means 4 situated at the transmitter supply a signature SG as a function of the message M which is to be transmitted. The message associated with its signature, as well as a common key E, are transmitted by the transmitter towards the receiver after coding by means of an intrinsic key R.sub.1. Upon being received, the message M linked with its signature SG is decoded by means of an intrinsic key R.sub.2 determined at the receiver location in such manner as to establish equality between intrinsic keys R.sub.1 and R.sub.2.

Abstract: A credit card includes a memory having first and second zones in which are respectively stored variable and fixed data. The data stored in the first zone includes first, second and third bit fields respectively representing a card serial number, a card invalidation character and a card validation character. The first, second and third bit fields are subject to change by improper use of the card. The first, second and third bit fields are read to derive first, second and third signals. The second signal is compared with a predetermined signal indicative of a desired value for the second field. A set of bits is written into the third field in response to the second signal being equal to the predetermined signal and the first signal being equal to a stored signal indicative of an assigned serial number. The set of bits written into the third field is tested to determine if the bits were properly written into the third field.

Abstract: A memory matrix is divided into a plurality of zones, one of which has a predetermined address and is set aside for a control character having multiple bits, stored in plural cells of the one zone. Each cell stores electric charge, with the cells in the control zone storing a charge no greater than that in the remaining zones. After the cells of the control zone have been initially supplied with the predetermined control character, the cells of the control zone are isolated from write command signals during normal operation. The cells of the control zone can be read out during normal operation.

Abstract: A control character having a predetermined sequence of binary values is written into a control zone of a memory matrix. It is impossible to alter the binary values in the control zone during normal operation of the matrix, but it is possible to read out the values stored in the control zone during normal operation. A comparison is made with the signals read out from the control zone during normal operation with predetermined values for the bits in the control zone, to determine if deleterious effects, during normal operation, have altered the data stored in the remaining zones of the matrix.

Abstract: A system for keeping account of predetermined homogeneous units by means of an article such as a card, carrying information which may be the amount of a credit balance, and an external device for operating on the information. In general, the balance on the card is initially validated. Thereafter, the balance is irrevocably drawn upon as desired until a zero balance is reached. In order to avoid a single large expenditure to validate the card, and at the same time to minimize the possibility of fraud, a memory in the card has a plurality of zones which are individually validatable. A separate validating field in the memory has validating bits corresponding to individual memory zones. The validity field is accessible by the external device only, and is protected by a coded key embodied in the card. To make the system usable for recording other than whole numbers of units, one of the zones may have a plurality of sub-zones. One of the sub-zones may be allocated to multiples or sub-multiples of individual units.