Abstract: In a system for the transmission of confidential data between a transmitter 1) and a receiver (3), the transmitter (1) transmits a standard key E to the receiver (3). The standard key E preferably is a random number generated within the transmitter (1). An element at the location of the transmitter (1) calculates an intrinsic key R.sub.1 for coding the data to be transmitted, and an element at the location of the receiver calculates an intrinsic key R.sub.2 for decoding the data. The calculation of each of the intrinsic keys R.sub.1 and R.sub.2 is accomplished in each case by a microprocessor (4' and 5') situated within a portable object (4 and 5) which also includes a memory (4" and 5") storing a program, a secret code S, and an identification code I.sub.n. The intrinsic keys R.sub.1 and R.sub.2 are each calculated as a function of the secret code S, the identification code I.sub.n, and the standard key E. The portable objects at the transmitter and receiver ends of the system must be matched.

Abstract: The user has a credit card incorporating electronic devices and/or circuits. The facility which is to be protected has an electronic device and/or circuit analogous to that of the credit card. The devices of the credit card and of the facility contain in their respective memories a secret code S, an identification code I.sub.n, and a program p. The facility which is to be protected has available a generator of a random code E which is transmitted into each of the devices when a request for access is made. The devices within the card and the facility each calculate the function R=p(S, E, I.sub.n), and a comparator situated in the facility which is to be protected compares the functions supplied by each of the devices to allow or deny access of the person to the said facility.