PROCEDE DE PROTECTION D'UN SYSTEME D'ACCES ET/OU DE DEMARRAGE MAIN LIBRE D'UN VEHICULE EN MODIFIANT LA VITESSE DE RECEPTION DE SIGNAUX

Method for improving the security of communication between the electronic key and vehicle to prevent interception by a third-party item of electronic equipment by highlighting in such event, a time delay in acknowledgement of this signal by the key. This method includes, before authorizing the access to and/or starting of the vehicle, additional steps of adapting the amplitude of a coded identification request signal received by the key to reach the detection threshold of the key as soon as possible; measuring the sum of the duration of the emission of the coded interrogation signal and of the duration of the response signal of the electronic key; comparing the sum of the measured durations to a reference duration, and triggering an alarm relating to the conditions of access to and/or starting of the vehicle when the separation between this sum of durations and the reference duration is above a preset threshold.