System for enhancing the security of a bi-directional data transmission system controlling access to an enclosed space, notably a vehicle

Abstract

The disclosure relates to a system providing enhanced security of a bi-directional data transmission controlling access to an enclosed space, including an identification device with a transmitting circuit and a receiving circuit installed in said enclosed space, and an identifier carried by a user wishing to gain access, a data interchange between said identification device and said identifier normally being established when the distance between them is less than a predetermined limit, the access being granted only when said identification device has authenticated said identifier, wherein, to prevent an interchange of identification data at a distance greater than said predetermined limit, notably by interposing an unauthorized repeater, the system includes means of switching that establish a momentary loopback of said transmitting circuit of said identification device, via a return circuit of said identifier , and said identification device includes means of measuring the resonance frequency of the oscillation generated by such a loopback, and means of control able to measure the difference between said resonance frequency and a reference frequency, so as to maintain access interdiction when this difference exceeds a predetermined value. The invention is notably applicable to secure control of access to a vehicle.