FR3007877A1 - METHOD FOR SECURING A FREE HANDLING ACCESS AND / OR STARTING SYSTEM OF A VEHICLE USING TEST SIGNALS - Google Patents

Abstract

The present invention relates to a method of securing a system for access and / or freehand start of a motor vehicle, in the case of transmission of electromagnetic waves. This method comprises, before the step of unlocking or starting the vehicle, steps of checking the interception of signals by third-party electronic equipment comprising a transmission by the vehicle of at least one test signal to the key electronic, at least two amplitude measurements made over periods (T1, T2) corresponding to different numbers of periods and starting (t'1, t'2) at the beginning of the received signal (28, 29) by the electronic key , a comparison between the measurements made (V1 ', V2') and when the ratio V1 '/ V2' is less than a predefined threshold, a warning trigger relating to the conditions of access to the vehicle or starting the vehicle.

Description

The present invention relates to a method of securing an access system and / or hands-free start for motor vehicles. The invention relates to vehicles equipped with an electronic key detection system for unlocking or locking the doors as well as authorization to start the engine of the vehicle. The system transmits information between a transmitter / receiver located in the vehicle and the electronic key carried by the user of the vehicle. The vehicles are equipped with complex electronic equipment designed to provide the driver with comfort of use and safety. Unlocking the vehicle and starting are thus facilitated by these electronic equipment. The transmission is carried out by radio signals, in the low-frequency domain, for example 125 kHz, for their transmission from the vehicle to the electronic key, and in an authorized radio frequency range, for example at 433 MHz or 315 MHz, for their emission from the electronic key to the vehicle.

The current evolution of unlocking the door and starting the vehicle called "free hand" allows to leave the electronic key in the pocket or bag of the driver while performing these actions. These systems are called for example PASE system, initials of "passive access and engine start" ("Passive Access and Start Engine" in English terminology) or PKES, initials of "keyless passive access and start system" (" Passive Keyless Entry and Start "in English terminology). These hands free systems are particularly advantageous because the driver no longer has to search his pocket or bag to find the vehicle key. However, these door unlocking and vehicle start systems without a physical key present a security problem: the use of wireless communications instead of the use of a physical key opens the possibility of intercepting the signals circulating over the air. between the vehicle and the dongle, even after the user has locked the vehicle. More specifically, the usual protocol of a free-hand access and start system comprises the following steps: - after detecting an unlock request - by approaching a hand, pressing a handle door or a key button or equivalent -, a call is launched by the transmitter of the vehicle, located in the passenger compartment and / or in the door handles, to authenticate the electronic key; these messages are sent in low frequency (so-called LF) and are short-range, about 1.5 to 2 m; if the electronic key of the vehicle is in the perimeter of this range, it transmits its encrypted response in the radiofrequency band (for example 433 MHz or 315 MHz) with a range between approximately 30 and 120 m; - if the signal received by the vehicle is validated, the doors are unlocked without physical contact; - when the user of the vehicle has settled inside and wishes to start it, the central unit must detect certain appropriate signs, for example pressing the start button, then another exchange of information is initiated with the dongle and it must be authenticated again. If these tests are successful, the vehicle starts. An introduction to this protocol is illustrated by the logic diagram of FIG. 1. After the initial step 1, called Start, the central unit is waiting for an unlocking request that can be carried out as indicated above. If the central unit receives an unlock request (test step 3), the vehicle sends (step 7) an encrypted digital identification request, each frame of which starts with an awakening header called WUP (initials of "Wake"). UP ") to the vehicle's electronic key. If the electronic key does not respond according to the protocol agreed in the test 8, the process is moving again to Step 1 Start. If the dongle responds correctly, the vehicle (step 9) unlocks to allow access to the user. When a start request is subsequently received by the central unit, this request is followed (step 11) by a new coded and encrypted authentication request sent by the central unit to the electronic key which must answer correctly (test 13) to allow start-up (step 15).

However, these communications can be easily intercepted, and signals to the vehicle intercepted by third-party electronic equipment are then re-transmitted to the vehicle. These third-party electronic devices are equipped with resonant electrical circuits which disturb the transmission and cause delays in the reception by the electronic key of the information transmitted by the vehicle. The invention aims to protect the communication between the electronic key and the vehicle, in order to prevent any interception. To this end, the invention highlights, in the event of a disturbance caused by this interception, a time-spreading rise in the amplitude of the signal received by the electronic key, based on amplitude measurements of said signal.

More specifically, the subject of the present invention is a method for securing an access and / or hands-free starting system of a motor vehicle equipped with at least one opening element, this method comprising: a transmission step a request for identification by at least one antenna on board the vehicle and receipt of the identification request by an electronic key; a step of sending a signal by the electronic key in response to the identification request; - A step of unlocking at least one of the opening (doors and tailgate) of the vehicle; and / or - an authorization step of starting the vehicle. In addition, this method comprises, before the unlocking and / or start authorization step, security steps, comprising transmitting at least one periodic type of test signal, in particular sinusoidal, and amplitude signal. substantially constant by the on-board antenna to the electronic key, at least two amplitude measurements made over predefined durations corresponding to different numbers of periods and beginning at the beginning of reception of the signal received by the electronic key, a comparison between the measurements taken to derive a safety factor and, when this safety factor is substantially different from a predetermined value, an alert trigger relating to the conditions of access to the vehicle. The term "security" refers to the verification of the presence or absence of signal interception by third-party electronic equipment. According to advantageous features, the method according to the invention provides that: the first amplitude measurement is performed over a number of periods to reach a constant value of the amplitude of the signal in the absence of interception and the second measurement over a substantially greater number of periods; a single test signal is transmitted and two amplitude measurements of the signal received by the electronic key are successively carried out; two test signals are emitted successively and an amplitude measurement is performed on each corresponding received signal; each amplitude measurement relates to the determination of the amplitude of the signal at the end of the number of periods on which the measurement is made; each amplitude measurement relates to the average amplitude of the signal determined over the number of periods on which the measurement is made; - the number of periods covered by the second measurement is at least twice the number of periods covered by the first measurement; - The safety factor refers to the ratio between the first and the second measurement, and the alert is triggered when this ratio is less than a ratio substantially equal to 0.9.

Other data, characteristics and advantages of the present invention will appear on reading the following nonlimited description, with reference to the appended figures which represent, respectively: FIG. 1, a logic diagram of the protocol of an access system and free hand start of the state of the art (already commented); FIGS. 2a to 2c, representations of the sinusoids of an example of a test signal emitted by the vehicle (FIG. 2a) and received by the key, in the absence (FIG. 2b) and in the presence of interception (FIG. 2c); and FIG. 3, an exemplary logic diagram for securing an access and hands-free start system according to the invention.

FIGS. 2a to 2c present the test signals according to the invention at their transmission (FIG. 2a), at their reception in the absence of interception (FIG. 2b) or in the presence of interception (FIG. 2c). FIG. 2a illustrates in detail the sinusoids of two test signals 21 and 22 according to the invention, transmitted at the low frequency of 125 kHz by a free hand access system antenna of a vehicle. They are separated by a rest period AT, equal to one millisecond in this example. The sinusoids of the test signals 21 and 22 have respectively 4 and 8 periods of constant amplitude A. FIGS. 2b and 2c show the signals received 25 to 29 by the electronic key, respectively in the absence (FIG 2b) and in the presence (FIG 2c) of an interception caused by an external equipment. The signals 25 and 26 (FIG. 2b) are the signals received by the electronic key respectively of the emitted test signal 21 and of the emitted test signal 22. They are received without interception. In this example, the electronic key contains a unit of measure which makes it possible to calculate the amplitudes at the end of predefined durations corresponding to numbers of selected periods. The predefined duration T1 of the first 4 periods of the first received signal lasts 32 microseconds, and allows this signal 25 to reach its maximum amplitude at the beginning of the plateau phase.

The preset duration T2 of the first 8 periods of the second received test signal 26, which lasts 64 microseconds, makes it possible to reach the plateau phase and to remain there for 4 periods, ie half of its duration. At the beginning of reception of each test signal, from the instants t1 and t2, the amplitude of the received signals 25 and 26 increases to reach plateau values V1 and V2, identical in the example (V1 = V2), to measurement uncertainties close. The allowed tolerance is 20% in this example. Thus, when V1 is at least 0.8 x V2, the method concludes that there is no interception. With reference to FIG. 2c, the signals 28 and 29 are received by the key respectively of the transmitted test signal 21 and of the transmitted test signal 22, in the case of an interception. The electronic key performs in this case the amplitude measurements V'1 and V'2, at the end of each of the predefined periods T1 and T2, with in this case V'1 substantially smaller than t V'2, here V'1 = 0.6 x V'2. Because of the interception, the predefined duration T1 of the first signal 28 is insufficient in this case to allow the amplitude of the signal 28 to reach its maximum V1 because the rise towards the plateau is spread over time, whereas this was possible in the case of no interception (see the signal received from Figure 2b). By comparison, the predefined duration T2 of the second signal 29 is sufficient for this signal to arrive at a level V'2 substantially close to or equal to its maximum of intensity V2. In this case, the condition "V1 at least equal to 0.8 x V2" is no longer respected, which allows the electronic key to detect the presence of an interception. The electronic key communicates this detection to the central unit which then triggers alarm alerts and / or preventive actions to block the unlocking or starting as detailed with reference to FIG. 3. The logic diagram of FIG. embodiment of the security method according to the invention. In the start step 33 "Start", the central unit is waiting for the detection of an unlock request, for example by pressing a key button. If an unlock request is detected (test step 34), the vehicle transmits (step 35) coded identification requests from which each frame begins with a header called WUP to the attention of the vehicle key. The dongle responds (answer step 36). If in the response step 36 the electronic key does not respond or responds improperly, the process is reset with return to step 33. Before unlocking the doors (door and tailgate) to the door. In step 49, security steps are advantageously implemented. The first security test called "test 1" (step 37) is the transmission of a first test signal 21 (FIG. 2a), followed by the measurement (step 39) of the amplitude V1 of the corresponding signal 25 (FIG. 2b). ) or 28 (Figure 2c) once received after the lapse of the duration T1. The method continues with a test called "test 2" (step 41), which consists of sending a second test signal 22 (FIG. 2a), followed by the measurement (step 43) of the amplitude V2 of the corresponding signal 26 (FIG. 2b or 29 (Figure 2c) once received after the lapse of the duration T2. Then the values of V1 and V2 are compared (step 45) by establishing their ratio V1 / V2 and submitting this report to a test (step 47). In a variant, the first and second test signals form a single signal whose amplitude is measured on reception from the same instant and after the flows of durations T1 and T2.

The test 47 consists of comparing the ratio of measurements V1 / V2 as a safety factor to a ratio k. If the ratio V1 / V2 is lower than the ratio k, in the example k = 0.80 (the ratio k may be assigned another value less than 1), the central unit is informed by the electronic key and triggers alerts and preventive actions (alert step 54), which can be an audible (vibration) and visual alert on the electronic key itself or on the vehicle, or a locking of the unlocking of the doors of the vehicle. Alternatively, the central unit is informed of all V1 / V2 ratio measurements, and analyzes this ratio itself. If, in the test 47, the ratio V1 / V2 is greater than 0.80, the method concludes that there is no interception and proceeds to the normal unlocking of the opening (step 49). During a consecutive request for start recognized by the central unit, for example by pressing the start button, the central unit performs all the security tests (step 51) in a similar way to the tests performed for the first time. securing the unlocking (37, 39, 41, 43, 45, 51). In the test of step 53, the ratio V1 / V'2 of the measured voltages must be greater than a ratio k '(k' = 0.8 in the example, the ratio k 'may be assigned a value equal to or different from that of k, while remaining less than 1) to allow startup without a physical key (start authorization step 55). If at the test of step 53 the ratio is less than k ', the method triggers at least one preventive action (step 57 of alert), for example: blocking of the start 30 without intervention of the physical key The invention does not is not limited to the embodiments described and shown. For example, for measuring signals, these signals can be measured at the end of their transmission, or before. Furthermore, characteristics other than the amplitude of these signals can be measured, such as, for example, the potential difference of the received current with respect to the potential of the key. It is also possible to apply tests according to the invention at different stages of the information exchange between the vehicle and the electronic key, for example at the encrypted request step sent to the electronic key before the step access authorization or before the start authorization step.

Claims (8)

REVENDICATIONS1. A method of securing an access system and / or hands-free starting of a motor vehicle equipped with at least one opening, comprising a step of issuing an identification request (35) by at least one antenna on board the vehicle and receiving the identification request by an electronic key, a step of responding (36) to the identification request by a signal transmission by the electronic key, an unlocking step (49) opening of the vehicle, and / or a starting authorization step (55) of the vehicle, characterized in that, before the unlocking step (49) or starting authorization (55), this method further comprises securing steps (37, 39, 41, 43, 45, 51), comprising transmitting at least one test signal (21, 22) of periodic type and substantially constant amplitude by the on-board antenna to of the electronic key, at least two amplitude measurements (V1, V2) performed over predefined durations (T1, T2) corresponding to different numbers of periods and starting at the beginning (t1, t2; 1'1, t'2) receiving the received signal (25, 26; 28, 29) by the electronic key, a comparison between the measurements made to deduce a safety factor (V1 / V2, V'1 / V 2) and, when this safety factor is substantially different (47, 53) from a preset value (k, k '), an alert trip (54, 57) relating to the conditions of access to the vehicle and / or starting it. 2. Method for securing an access system and / or free hand start according to the preceding claim, characterized in that the first measurement (V1, V'1) is performed over a number of periods to achieve a constant value of the amplitude of the signal in the absence of interception and the second measurement (V2, V'2) over a substantially greater number of periods. 3. A method of securing an access system and / or free hand start 25 according to any one of the preceding claims, characterized in that a single test signal is transmitted and two amplitude measurements of the signal received by the electronic key are successively performed. 4. A method of securing an access system and / or free hand start according to any one of claims 1 to 2, characterized in that two test signals (21, 22) are emitted successively and a measurement of amplitude (V1, V2, V'1, V'2) is performed on each corresponding received signal (25, 26, 28, 29). 5. Method for securing an access system and / or free hand start according to any one of the preceding claims, characterized in that each amplitude measurement relates to the determination of the amplitude of the signal (V1 , V2; V'1, V'2) at the end of the number of periods (T1, T2) on which the measurement is made. 6. A method of securing an access system and / or free hand start according to any one of claims 1 to 4, characterized in that each amplitude measurement relates to the average amplitude of the signal determined on the number of periods (T1, T2) on which the measurement is made. 7. A method of securing an access system and / or free hand start according to any one of the preceding claims, characterized in that the number of periods (T2) on which bears the second measurement is at least twice higher than the number of periods (T1) to which the first measurement relates. 8. A method of securing an access system and / or free hand start according to any one of the preceding claims, characterized in that the safety factor relates to the ratio between the first and second measurements (V1, V2; V'1, V'2), and the alert is triggered when this ratio is less than a ratio substantially equal to 0.9.