FR2812679A1 - REMOTE CONTROL ANTI-PIRACY METHOD FOR MOTOR VEHICLE AND SYSTEM FOR ITS IMPLEMENTATION - Google Patents

Abstract

This remote control method for controlling a component (O) of a vehicle, consisting in establishing a bidirectional dialogue between a central unit (1) carried by said vehicle and an identification device (I) intended to be carried by a user, said dialogue comprising at least a first communication, of a first signal (S1) sent from said central unit to said identification device and a second communication, of a second signal (S2) sent from said identification device to said central unit, is characterized in that it comprises the steps of: triggering said first communication; initiating said second communication; issuing an activation order (38); a step of successive phase comparisons, simultaneously with said first and second communications, said activation of an activation command being prohibited as soon as the result of said successive comparisons () meets a predetermined criterion.

Description

The present invention relates to a method for remote control of a

  member of a motor vehicle, in particular a locking member for access to said vehicle and / or a starting device, and also a control system for carrying out this method. Such a control system is for example used to allow access said hands-free to a vehicle, and / or said hands-free start of said vehicle; "hands free" meaning that it is not necessary to use

a key for these operations.

  As can be seen in FIG. 1, such a system generally comprises an identification device I intended to be worn by a user U and able to establish a bidirectional remote and wireless communication with a central control unit 1 on board the vehicle V , to authenticate the user and to control means for locking / unlocking the locks of the doors when the user has been recognized as genuine. Initialization of the communication protocol can be activated by operating the outside door handle, for hands-free access, or by pressing a start button, in the hands-free start mode. As a variant, this initialization can be triggered by actuating a control button of the identification device I. A system currently proposed consists in using low-frequency carrier waves of the order of 125 kHz for communication from the vehicle to the vehicle. identification device I, and ultra-high frequency carrier waves, for example of the order of 434 or 868 MHz, for the Europe zone, and 315 or 902 MHz for the USA zone, for the communication from the device. identification I to the vehicle V. The identification device I must include a battery to power its own electronic circuits. To minimize the power consumption, it can be provided, for example, that the identification device is dormant for 9 ms and waking 1 ms,

for periods of 10 ms.

  As can be seen in FIG. 1, the bidirectional dialogue comprises a first communication of a first signal Si sent by a first transmitter 2 of the central unit 1 to a first receiver 3 of said identification device I and a second communication of a second signal S2 emitted by a second transmitter 4 from said identification device I to a second receiver 5 of the central unit 1. Here, the signal term is used to designate a sequence, continuous or

interrupted, of data.

  The power of the transmitters 2 and 4 and the efficiency of the receivers 3 and 5 is such that the first and second communications can take place only when the identification device I is at a distance less than or equal to a predetermined communication distance. dc of the vehicle V, generally of the order of a few meters, to avoid, on the one hand, interference with other signal sources of the environment, and, on the other hand, to avoid the operation of the system to a distance such that the user U is too far from the vehicle V to be aware of the operations carried out

by said system.

  For user authentication purposes, said first signal Si comprises data characteristic of said vehicle to be recognized by said identification device and / or the second signal S2 comprises data characteristic of said identification device to be recognized by said vehicle. The bidirectional dialogue between the vehicle and the identification device can be encrypted, in order to avoid any inadvertent operation of the system and to secure it against the perpetrators. However, despite the possible encryption, there is a way to hack the system without knowing the characteristic data. This piracy method is shown in FIG. 2. According to this method, it is assumed that the user U carrying the identification device I is located at a distance from the vehicle V greater than the authorized communication distance,, for example from 10 to 100 m distance from the vehicle. In this case, a pirate equipped with a first relay box 6 can approach the vehicle V at a distance dc 'sufficient to communicate with it, for example at a distance of the order of 1 to m. This hacker activates the beginning of the communication, for example by pulling on the outside door handle. This triggers the transmission of said first signal Si by the vehicle V to the relay box 6. This signal Si sent by the vehicle is received by the relay box 6, which comprises a receiver 8 at 125 kHz. This receiver 8 is connected to a transmitter 9 at high frequency, of the order of several MHz. The transmitter 9 transmits, as represented by the arrow 10, to a second relay box 11, which is carried by another hacker following the user U at a distance of the order of a few meters. The exchange of information between the two relay boxes 6 and 11 is performed at very high frequency, it is possible to perform this communication at a distance dp very large, of the order

  several tens or hundreds of meters for example.

  The second relay box 11 comprises a receiver 12 at the same frequency as the transmitter 9 of the first relay box 6. The signal thus received is retransmitted at the frequency of 125 kHz by a transmitter 13 in order to send a signal 14 to the identification device I which complies with the signal Si emitted by the vehicle. The signal 14 being the repetition of the authentic signal SI of the vehicle, the identification device I will recognize it and in turn transmit its response signal S2, said response signal S2 being sent at high frequency, by

  example at 434 MHz and received by a receiver 15 of the second housing-

  relay 11, which will convert the 434 MHz signal into a signal at a different frequency, for example at 315 MHz. The converted signal 17 is then transmitted by a transmitter 16 to the first relay box 6, this frequency difference being necessary so that the different signals do not interfere with each other. Of course, the frequency of the signal 17 is different from both the frequency of the signal 10 and the signal S2. This signal 17 is picked up by the first relay box 6, which comprises a receiver 18 of the same frequency as the transmitter 16. The receiver 18 is connected to a transmitter 19 which transforms the signal at 315 MHz into a signal S2 'to 434 MHz, according to the signal S2 issued by the identification device I, which is sent to the vehicle V. To detect such hacking and interrupt the communication, one solution could be to use ultra-fast microwave communications. However, such a high-speed system using microwave would have a significant additional cost. There is a significant economic interest in keeping the

  existing systems using frequencies of the order of 125 kHz.

  The risks of piracy by the method described above are due to the fact that it can be implemented using electronic components commercially available in common, in video equipment for example. A relay box designed with such components would have a limited bandwidth, for example less than 1 MHz. The processing time required between the reception by the receiver 8 of the device 6 of a data carried by the signal S1 and the transmission by the transmitter 9 of this same data in the signal 10 would then be of the order of microsecond (its). Thus, the signal S2 ', received by the receiver 5 in the case of the hacking attempt shown in FIG. 2, would have, with respect to the signal S2 that would have been received in the case of a normal use of said control system, as shown in FIG. 1, a transmission delay Δt of the order of 4 to 5 Ès. The calculation of the transmission delay Δt generated by the piracy method described above will be detailed below. The transmission delay Δt is negligible in comparison with the time constants necessary for the authorized normal transmission. For example, the total communication can be of the order of 20 to 40 milliseconds (ms), and the total duration of operation of the system to trigger the unlocking or condemnation of the electric locks can be of the order of 100 ms. On the other hand, the delay of transmission At is of the order of half of the

  TBF period of the low frequency carrier wave at 125 kHz.

  The present invention aims to eliminate the aforementioned drawbacks and to provide a method and a remote control system for a motor vehicle to prevent hacking of the system, in particular via relay boxes, taking into account the propagation time and signal processing between the vehicle and the identification device. The proposed control system can be realized from existing systems

  operating at a frequency of 125 kHz.

  For this, the invention provides a remote control method for controlling a member of a motor vehicle, in particular means for locking the access to said vehicle and / or means for starting said vehicle, consisting in establishing a bidirectional dialogue. over the air between a central unit carried by said vehicle and a portable identification device intended to be worn by a user, said dialogue comprising at least a first communication, continuous or interrupted, of a first signal transmitted from a first transmitter of said central unit to a first receiver of said identification device and a second communication, continuous or interrupted, of a second signal transmitted from a second transmitter of said identification device to a second receiver of said central unit, said dialogue being unable to establish that if the distance separating said central unit from said identification device is sensitive less than a predetermined communication distance, said method being characterized by comprising the steps of: (i) triggering said first communication, said first signal being carried by a first carrier wave; (ii) triggering said second communication, said second communication being at least partially unwound while said first communication continues, said second signal comprising an identification signal of said identification device and a phase signal, said image, representing the phase of said first carrier wave received by said identification device; (iii) transmitting an activation command for activating said member after receiving said identification signal by said central unit; said method also comprises, simultaneously with said first and second communications, a step of successive comparisons between the current value of the phase represented by said image phase signal received by said second receiver, and the current value of the phase of a signal of reference, according to the carrier wave being transmitted by said first transmitter delayed a predetermined reference delay, zero or non-zero; the phase represented by said image phase signal having, during said comparison step, a transmission delay with respect to the phase of said carrier wave being transmitted by said first transmitter, said activation command transmission being prohibited as soon as the result of such comparisons

  successives fulfills a predetermined cancellation criterion.

  Preferably, the phase of said first carrier wave

  undergoes a random modulation during the duration of its emission.

  In this case, said random modulation advantageously comprises the introduction of phase jumps in said first carrier wave at successive random instants at irregular intervals greater than or equal to a predetermined modulation period. Advantageously, said modulation period is substantially greater than the period of said first carrier wave; preferably of the order of 5 to 10 times the period of said first carrier wave. Preferably, the amplitude of said phase jump is

substantially fixed.

  Preferably in this case, the ratio between said amplitude and said modulation period is significantly lower than the fundamental frequency of said first carrier wave, preferably less than

  1 / 5th of this fundamental frequency.

  Preferably, the phase represented by said image phase signal has, with respect to the phase of said carrier wave, alterations introduced by the identification device as a function of said phase jumps according to a predetermined algorithm known to said

central unit.

  According to another characteristic of the invention, said transmission delay being dependent on the time required for the path of said first signal between said central unit and said identification device and the time required for the path of said second signal between said identification device and said central unit, said reference delay is chosen substantially equal to a predetermined normal delay, said normal delay being the substantially fixed value of said transmission delay when the distance separating said central unit from said identification device is substantially lower than said predetermined communication distance . In a particular embodiment of the invention, said cancellation criterion is validated if the difference between said two values of

  compared phase exceeds a predetermined maximum level.

  In another particular embodiment of the invention, the difference between said two compared phase values comprises the sum of a so-called continuous component, substantially constant over a duration greater than said modulation period, and a fluctuating component over the duration of said modulation period, said cancellation criterion being validated as soon as the absolute value of said component

  continuous exceeds a first predetermined threshold.

  Preferably in this case, said cancellation criterion is validated as soon as the integral of the amplitude of said fluctuating component over a predetermined integration time exceeds a second predetermined threshold. The present invention also provides a system for carrying out the method described above, comprising said central unit and said portable identification device, characterized in that said central unit comprises a first microcontroller linked to said member to deliver said said activation command, said first radiofrequency transmitter linked to said first microcontroller for transmitting said first carrier wave and said first signal, said second radio frequency receiver for receiving said second signal, a phase comparator module coupled to said second receiver and said first transmitter for effector said successive comparisons, a decision module linked to said phase comparator module for receiving the result of said comparisons and linked to said first microcontroller to deliver a cancellation signal of said activation order transmission as soon as said cancellation criterion is validated ; said identification device comprising said first radio-frequency receiver for receiving said first signal, a second microcontroller for generating said identification signal, said second radio-frequency transmitter for transmitting said second signal, said second transmitter being linked to said first receiver for receive said image phase signal and said second

  microcontroller for receiving said identification signal.

  Advantageously, said central unit comprises a random signal sequence generator linked to said first transmitter for modulating the phase of said first carrier wave during its first transmission.

program.

  Preferably, said random signal sequence generator is able to deliver periodically to said first transmitter a random binary signal, said first transmitter being able to introduce a phase jump in said first carrier wave each time

  said received binary signal takes a predetermined value.

  According to another characteristic of the invention, said identification device comprises a demodulator connected to the first receiver for receiving said first carrier wave and the second microcontroller to deliver said demodulated random bit signal of said first carrier wave; said second microcontroller being adapted to modify said image phase signal as a function of said signal

random binary.

  Preferably, said decision module comprises a low-pass filter whose input is connected to the output of said phase comparator module and whose output is connected to a signal comparator to compare the difference between said two phase values compared. audit

predetermined maximum level.

  According to yet another characteristic of the invention, said decision module comprises a high-pass filter whose input is connected to the output of said phase comparator module in order to extract said fluctuating component from said result of the comparisons and whose output is connected to a second comparator, distinct or otherwise from the signal comparator, for comparing said fluctuating component with said second predetermined threshold. Advantageously, said first transmitter is able to transmit said first signal by amplitude or phase modulation of said

first carrier wave.

  The invention will be better understood, and other objects, details, features and advantages thereof will become more clearly apparent in the art.

  during the following description of a particular embodiment of

  the invention, given solely for illustrative and non-limiting purposes, with reference to the accompanying drawing. In this drawing: - Figure 1 is a block diagram of operation of a remote control method according to the invention in normal operation; FIG. 2 is a block diagram of the operation of a remote control method according to the invention during a hacking attempt; FIG. 3 is a block diagram of a system for carrying out the method according to the invention; FIG. 4 is a chronogram showing schematically the signals compared in the system of FIG. 3 during the normal use of the system and an attempted hacking; FIG. 5 is a chronogram showing schematically the signals compared in the system of FIG. 3 during an attempted hacking after insertion of a phase jump in the first carrier wave; FIG. 6 is a detailed and enlarged view of the decision module of the system defined by the frame VI of FIG. 3 in a first embodiment; FIG. 7 is a timing diagram showing a phase signal received by the decision module of FIG. 6 for different values of the transmission delay between the compared signals; FIG. 8 is a timing diagram representing the phase signal received by the decision module of FIG. 6 for particular values of the transmission delay; FIG. 9 is a detailed and enlarged view of the decision module of FIG. 6 in a second embodiment; FIG. 10 is a timing diagram showing the fluctuating portion of the phase signal received by the decision module of FIG. 9 during normal use of the system; FIG. 11 is a timing diagram showing the same the fluctuating part of the phase signal as in FIG.

an attempt to hack.

  - Figure 12 a block diagram of a variant of a part of the system of Figure 3 delimited by the frame XII; FIG. 13 is a timing diagram representing the phase signal received by the decision module of FIG. 6;

  when the fitness module of Figure 12 is used.

  The control method according to the invention uses a bidirectional dialogue over the air between a central unit 1 carried by a vehicle V to control one of its members O, visible in FIG. 3, and a portable identification device I intended to be carried by a user U of said vehicle. The control system for implementing the method according to the invention comprises the central unit 1 and the portable identification device I, which will now be

  described with reference to FIG.

  The central unit 1 comprises a first microcontroller 20 connected to said member O, which can notably be a contact switch or a door lock, by a communication network 21. The microcontroller 20 is generally in a state of semi-sleep or of waiting for an awakening. When the user actuates the outside door handle, not shown, an activation signal is sent to the microcontroller 20, as indicated by the arrow 22. In response, the microcontroller sends a general supply signal, to supply the various components Then, the microcontroller 20 generates the signal Si to communicate to the identification device I and sends it to the input of a low frequency generator 24 to modulate in amplitude or in phase the carrier wave. at low frequency 27 that it generates. The low frequency generator 24 has a fundamental frequency fo for example of the order of 125 kHz. The output of the low frequency generator 24 is connected to an amplifier device for amplifying the carrier wave 27 carrying the signal Si. The first transmitter 2 comprises said low frequency generator 24 and said amplifier device 25. The output of the amplifier device 25 is connected to antennas 26 to transmit to the identification device I the carrier wave 27 carrying the signal Sl. The antennas 26 comprise several identical antennas, for example three or more, located at different points of the vehicle V to allow the emission of the wave 27 in several directions around the vehicle V. Preferably, the antennas 26 comprise a 26g antenna on the driver's door, an antenna 26d on the front door of the passenger, and an antenna 26c on the trunk of the vehicle V. Conventionally, each antenna 26 has a

  capacitance connected in series to a coil with a core connected to ground.

  The wave 27 is received by antennas 28 of the identification device I with attenuation depending on the propagation distance. The antennas 28 each comprise a winding connected in parallel with a capacitance of which one terminal is connected to ground, the respective windings of the three antennas 28x, 28y and 28z having mutually orthogonal axes so that the carrier wave 27 can be detected whatever its polarization and whatever the orientation of the identification device I. The three antennas 28 are respectively connected to three inputs 3x, 3y and 3z of the low frequency receiver 3. That of the antennas 28 which is the best oriented is thus able to produce an amplitude of 2 mV. The identification device I comprises a second microcontroller 30, the second transmitter 4 and a battery (not shown) to supply its various elements, the low frequency receiver 3 being preferably low consumption. The receiver 3 has a first output connected to a fitness module 31 and a second output linked to the microcontroller 30 to deliver it the first signal SI obtained by demodulation of the carrier wave 27. The receiver 3 sends to the reset module form 31 a crimped signal 64 reproducing, in a clipped form, the carrier wave 27 as it receives, without demodulation, so that the fitness module 31 eliminates the noise generated during the first communication. In an alternative embodiment of the invention which will be explained below, the fitness module 31 is also able to reduce the frequency of the crenellated signal 34 to a fraction of the fundamental frequency f 0, so as to make it suitable for transported by the second transmitter 4 on a carrier wave 35. The crenellated signal 34 may also include alterations with respect to the transitions of the low frequency carrier wave 27, introduced according to an algorithm

predetermined.

  The crenellated signal 34 at the output of the fitness module 31 reproduces the transitions of the low frequency carrier wave 27 as emitted by the transmitter 2, possibly at a reduced frequency, possibly with desired alterations and without disturbances. parasites. A two-input toggle switch 32 is controlled by the second microcontroller 30 by a line 33 to generate the second signal S2. The rocker switch 32 has a first input linked to the fitness module 31 to receive the signal 34 and a second input linked to the second microcontroller 30 to receive an identification signal Si, generated by the second microcontroller 30. According to the position of said flip-flop, the second signal S2 outputted from said flip-flop 32 to the second emitter 4 is alternately composed of data sequences of the identification signal Si and data sequences reproducing the low-frequency carrier wave 27. second transmitter 4 is ultra-high frequency, for transmitting the second signal S2 by frequency modulation of a carrier wave 35 of fundamental frequency, for example of the order of 434 MHz. The carrier wave 35 is transmitted via an antenna 36 of the second transmitter 4 to an antenna 37 connected to the second receiver 5 of the central unit 1. The ultra-high frequency receiver 5 is able to demodulate the carrier wave 35 which it receives to transmit at its output the signal S2 to the first microcontroller 20. The microcontroller 20 is able to authenticate the identification signal Si contained in the signal S2 that it receives, and to issue an activation command 38 to the organ O after

  the authenticity of the identification signal Si has been recognized.

  Alternatively, the second signal S2 may be emitted by amplitude modulation of the carrier wave 35. In this case, the toggle switch 32 is replaced by a summing module and the signal S2 is formed by amplitude modulation. signal 34 within said summing module (not shown). The signal S2 then simultaneously comprises, and no longer alternatively, the identification signal Si and the signal 34 reproducing the transitions of the wave

low frequency carrier 27.

  Preferably, the second microcontroller 30 is linked to a permanent memory 56 where are stored identification and encryption data characteristics of said identification device I, to use these identification data in the authentication of the first signal Si and / or the generation of the identification signal Si. The first microcontroller 20 is also linked to a permanent memory 49 where are stored identification and encryption data characteristics of said vehicle V, in order to use these identification data in the generation of the first signal Sl and / or the signal authentication

Si identification.

  The remote control method according to the invention makes it possible to provide an anti-piracy function, by making it possible to detect the transmission delay At generated by an attempted hacking by the method described above. To detect the presence of the transmission delay At, the central unit 1 comprises a phase comparator module 40 whose two inputs are respectively connected to the low frequency generator 24 and the second receiver 5, and the output of which is connected to a module decision 43 to deliver a phase signal (). The decision module 43 is connected to the microcontroller 20 to deliver a cancellation signal An when the phase signal <(satisfies a predetermined cancellation criterion.) The phase signal (<is a voltage signal which is between a minimum value, for example equal to -0.75V, taken when the phase shift measured by the phase comparator module is substantially zero (modulo 2r) and a maximum value, for example equal to + 0.75V, taken when the phase shift measured by the

  phase comparator module 40 is substantially n (modulo 2z).

  The calculation of the transmission delay generated by the hacking method described above will now be made with reference to FIGS. 1 and 2. In the normal use of the control system, as shown in FIG. 1, assume that a given transition of the low-frequency wave 27 carrying the signal S1 is reset at time t1 by the transmitter 2. This transition is received by the receiver 3 at time t2, separated from the instant t1 by the propagation time of the low frequency carrier wave 27 over the distance separating the vehicle V from the portable identification device I, that is substantially from dJc, oc is the speed of light in the air, substantially equal to 3.0.108 m / s. This same transition is represented by a part of the signal 34 included in the signal S2. The second ultra-high frequency transmitter 4 emits this part of the signal 34 at the instant t3, separated from the reception instant t2 by a response delay R, due to the signal processing time by the first receiver 3, the module 31 and the second transmitter 4. The portion of the signal S2 representative of this same transition of the low frequency carrier wave 27 is received by the second receiver 5 at time t4; then it is finally received by the phase comparator 40 at time tB after a reception delay Q due to the reception and processing of the second signal S2 in the second receiver 5. Thus, tB is substantially: tB = ti + P + R + Q, where P = 2dIc is the total propagation time of the electromagnetic wave to go back and forth between the

  vehicle V and the identification device I, which is of the order of 13.2 ns.

  The delays Q and R are for example of the order of 2 to 10 ps each. Thus P can be neglected in front of Q and R. When using the piracy method described above, shown in FIG. 2, suppose that a given transition of the low frequency wave 27 carrying the signal Si is emitted at the instant This transition is received by the receiver 8 of the first relay box 6 at time t2 ', separated from the instant th by the propagation time of the low frequency carrier wave over the distance. The part of the signal 10 representative of this same transition is emitted by the transmitter 9 of the first relay-box 6 at the instant t3 ', separated from the instant t2' by the second gearbox 6. response time Tr of the relay box 6, which is substantially of the order of 1! This part of the signal 10 is received by the receiver 12 of the second relay box 11 at time t4 ', separated from the instant t3' by the propagation time of the wave over the distance dp separating the two relay boxes 6 and 11. This portion of the received signal 10 is converted in the second relay box 11 into a part of the signal 14 representative of the same transition and transmitted by the transmitter 13 at time t5 ', separated from the instant t4 by the response time Tr of the second relay box 11,

  substantially equal to the response time of the first relay box 6.

  The identification device I receives said part of the signal 14 at the instant t6 'and responds to the part of the signal S2 representative of this same transition at the instant t7', with the same response delay R as during the use normal system. The propagation and processing times of the signals S2, 17 and S2 'constituting the communication of the identification device I to the vehicle V are identical to the times involved in the communication of the signal S1. The part of the signal S2 'representative of said transition of the low frequency wave transmitted at time t1 is received by the second receiver 5 at an instant t12', and finally received by the phase comparator module 40 at the instant tB ', substantially equal to: tB' = tl + 2dt / c + R + Q + 4Tr. The total propagation time 2d / c is of the order of 100 to 1000 ns for a distance dt of between 15 m and 150 m. It has thus been shown that the signal representing the transition emitted at th is finally received by the phase comparator module 40 with a transmission delay Δt = tB'-tB of the order of 4 to 5 μs in the case of an attempt of hacking with relay boxes compared to the case of normal use of the system. Most of the delay

  It is due to the response time Tr of the relay boxes.

  In a preferred embodiment of the invention, the low frequency generator 24 is able to delay the signal 41 transmitted to the phase comparator module 40 by an operational delay Dr relative to the carrier wave 27. The operational delay Dr is chosen substantially equal to the sum of the response delay R of the identification device I and the reception delay Q. The transition of the carrier wave 27 transmitted at the instant t1 is thus received by the phase comparator module 40 in the signal 41 at time tA = tI + Dr tB. The delayed signal

  41 serves as a reference signal in the phase comparator module 40.

  The signal 42 received by the phase comparator module 40 comprises the signal 34 representative of the carrier wave 27. This signal 42, for its part, has a delay (tB-tI) relative to the reception by the phase comparator 40. to the carrier wave 27 generated by the low generator

frequency 24.

  The operation of detecting a hacking attempt by the system according to the invention will now be described with reference to FIGS. 4 to 13. FIG. 4 shows, for a given period TBF, the signal 41 conforming to FIG. the carrier wave at low frequency 27 and delayed the operational delay Dr relative to it. The

  curve 44 represents the phase of this signal varying over the interval [0, 2n [.

  The signal 41 is represented as a sinusoidal signal for the sake of clarity, but in practice it can be clipped so as to be substantially a crenellated signal whose transitions correspond to the passages

  by the null value of the sinusoidal signal represented.

  In the case of normal use of the system according to the invention, at a given instant to, the phase of the signal 41 at the input of the phase comparator 40 is represented by the point A, and the phase of the signal 42 is represented by the point B The phase shift pB between the signals 41 and 42 compared by the phase comparator 40 is (pB = 2n (tB-tA) / TBF, which is of the order of 0.01 radians.) In other words, the phase shift measured by the phase comparator 40 is substantially zero in this case.In contrast, in case of attempted piracy using relay boxes, the phase of the signal 41 is unchanged, but the phase of the signal 42 at the same time to The measured phase shift is then gpB '= 2n (tB'-tA) / TBF, ie (pB' = 2At / TBF, which is substantially greater than n radians.) Like the vehicle and the carrier of the identification device I can not move a significant distance from the wavelength of the wave 27 during said di alogue, whose total duration is substantially a fraction of a second, the delay of

  At transmission is substantially constant throughout this duration.

  Thus, the phase shift PB 'proportional to the transmission delay At is

  substantially constant throughout the duration of said dialogue.

  With the simple phase shift measurement described above, an attempt to pirate using relay boxes could not always be detected. Indeed, in the case where the transmission delay At is equal to an integer N greater than or equal to 1 of periods TBF, with reference again to FIG. 4, the phase of the signal 41 represented by the point A is unchanged, but the phase of the signal 42 at the same given instant is represented in this case by the point B ". The measured phase shift is then substantially (pBq" = 2Nn, therefore, the phase signal CI is substantially minimal. in FIG. 4, the integer number N is equal to 1. To also detect an attempted hacking with such a well-chosen transmission delay, the method and the system according to the invention use a random modulation of the phase of the wave.

carrier 27.

  For this purpose, the control system according to the invention comprises, in the central unit 1, a random signal sequence generator 39 controlled by the microcontroller 20 and connected at the output to the low frequency generator 24 to randomly modulate the phase of the generated carrier wave 27. Preferably, the phase modulation of the carrier wave 27 is performed as follows: the random signal sequence generator 39 periodically delivers with a

  modulation period Tm, a modulation bit bm equal to 0 or 1.

  The transmission of the modulation bits bm is controlled by clock signals delivered to the generator of random signal sequences.

  by the microcontroller 20, which comprises a clock (not shown).

  The modulation bits bm are transmitted to the low frequency generator 24 by a voltage signal Vm which can take a high value h and a low value t. The voltage signal Vm makes a transition between its two values h and t whenever a bit of value 1 is emitted, and keeps

a constant value in the meantime.

  If the value of the modulation bit bm received by the low frequency generator 24 is 0, the generated carrier wave 27 is unchanged; if the value of the modulation bit bm received by the low frequency generator 24 is 1, the low frequency generator 24 instantaneously undergoes a phase jump of amplitude 5 (p to the carrier wave 27. The generated phase jumps the generator 24 is alternately a phase advance and a phase delay.The signal 41 delivered by the generator 24 to the phase comparator 40 is of course still in conformity with the wave

  carrier 27, following its phase jumps.

  Referring back to FIG. 4, suppose that the transmission delay Δt is such that the measured phase shift qB "is substantially equal to 2r at said instant to given, After the flow of one or more modulation periods Tmn, a first In fact, the opposite case would indicate that the random signal generator 39 generates only O, which is excluded. the carrier wave 27 has the effect of suddenly transforming the curve 41 into the

  curve 41 'sketched in Figure 4, as shown by the arrow 51.

  In this example, the first phase hop is a phase delay

of amplitude 8 (p equal to x / 2.

  FIG. 5 shows the signal 41 'in which the phase jump has been reflected, as well as its phase 44', and the signal 42 in which, because of the delay substantially equal to an integer greater than or equal to 1 of TBF periods that it has with respect to the signal 41, the phase jump has not yet been passed on, as well as its phase 50. Between the insertion of the first phase jump and the insertion of the next phase jump, whose date is by definition random, the phase comparator 40 compares the phase 44 with the delayed phase 50 of TBF. Thus, the phase shift measured by the comparator module 40 becomes, as represented in FIG. 5, substantially equal to & p. After the passing of an additional modulation period Tm, either the modulation bit generated will be a 0 and the carrier wave 27 will remain continuous, or the modulation bit bm generated will be a 1 and the carrier wave 27 will be advanced. of phase of amplitude equal to 6 (p) Because of the unpredictable succession of phase jumps 8 (p of the carrier 27, it is then no longer possible to choose the transmission delay At so as to produce a

  phase shift measured PB "which remains permanently zero.

  Due to the random phase modulation of the carrier wave 27 described above, the QI phase signal at the output of the phase comparator 40 has, in superposition, a DC component (IO and a fluctuating component (f whose amplitude The random phase modulation of the carrier wave 27 has the effect of frequency spreading the signal S 1. More specifically, the carrier wave 27 of fundamental frequency f0 has, after

  frequency modulation, a spectrum spread out substantially in the range [f0-

  & p / (2nTm), f0 + 9 (p / (2cTm)] The choice of the phase jump 8p and the modulation period Tm must therefore be done with the concern of respecting the regulation on the spectral width of the signals emitted in In order to reduce the frequency spreading, it is possible to lengthen the modulation period Tm or to reduce the amplitude of the phase jump (p The modulation period Tm is thus chosen greater than or equal to the low signal period. Preferably, the modulation period Tm is of the order of 5 to 10 times TBF, ie 40 to 80 μs Thus, as in the example shown in FIG. 11, the modulation period Tm is preferably longer than the transmission delay At. The typical frequency ff of fluctuations of the fluctuating phase signal (f is therefore of the order of 1 / At, ie for example a few

tens of kilohertz (kHz).

  The phase QI signal at the output of the phase comparator module 40 is sent to a decision module 43 able to detect the

  presence of a significant phase shift between the signals 41 and 42.

  In a first embodiment, visible in FIG. 6, the decision module 43 comprises a low-pass filter 65 of cut-off frequency fc, for example substantially equal to 100 kHz, in order to suppress noise, connected in series with a comparator. signal comparator 66 with a predetermined maximum level E. The signal comparator 66 is adapted to supply the microcontroller 20 with the cancellation signal An when the value of the phase signal Q is greater than the maximum level E. In FIGS. 7 and 8, has represented the evolution of the Q signal received by the signal comparator 66 as a function of time, around the transmission of a modulation bit bm of value 1, represented by the transition carried out at time t1 = 100pls by the voltage signal Vm, represented by the curve 73. At each transmission of a modulation bit bm of value 1, the corresponding phase jump, of amplitude 9p chosen equal to n in this example, is reflected on the signal reference number 41 with e operational delay Dr and on the signal 42 with the delay At + Q + R. Thus, the phase I signal has from time t1 + Dr a slot of time width substantially equal to the delay of

  transmission At. Because of the low-pass filter 65, this slot is rounded.

  Curve 67 represents the phase I signal for a transmission delay Δt = 0.2 pts, i.e., typical of normal system use. It can be seen that the phase I signal is substantially constant, with a value substantially equal to -0.75V. An oscillation 68 marks the location of the slot corresponding to the phase jump introduced at t. The oscillation 68 is of very low amplitude because it is very attenuated by the low-pass filter 65. The curve 69 represents the phase 1 signal for a transmission delay Δt = 2 gs. In this case, the signals 41 and 42 compared are in quadrature. We see that the phase signal

  oscillates weakly around a value substantially equal to 0V.

  The oscillation 70 marks the phase jump introduced at t. The curve 71

  represents the phase signal (1) for a delay of transmission At = - 4 ls.

  In this case, the signals 41 and 42 compared are in phase opposition.

  It can be seen that the phase signal <I oscillates weakly around a value substantially equal to + 0.75V. The oscillation 72, of greater amplitude than the previous ones because less attenuated by the filter 65, marks the phase jump introduced at ti. With these three examples, it can be seen that the choice of a threshold E substantially equal to -0.5V makes it possible to detect a transmission delay greater than or equal to 2 μs. In these examples, it is the average value of the phase signal (D which allows the detection and the

  phase jumps are not exploited.

  In FIG. 8, the phase signal () is represented when the transmission delay Δt is an integer of periods TBF. For curve 74, the transmission delay is At = 8ps = TBF. In this case, it is found that the phase signal 1 is on average substantially equal to -0.75V, but that it has a large oscillation corresponding to the phase jump introduced at t1. This oscillation, whose temporal width is 8 gs, is not attenuated by the filter 65, so that the phase signal (momentarily crosses the threshold E = -0.5 V. The curves 75, 76 and 77 represent the signal of phase () in the case of a transmission delay At equal to 2, 4 and 8 TBF, respectively, it is found that the oscillation corresponding to the phase jump introduced at th double of width from one curve to another and its maximum value approaches 0, 75 V. Thus, the four examples of FIG. 8 show that the threshold E = -0.5V also makes it possible to detect any transmission delay At substantially equal to one

  integer N greater than or equal to 1 of TBF periods.

  In FIGS. 7 and 8, the phase signal D is represented as produced by an analog system, but it is understood that a digital processing system can be used to obtain a digital signal.

equivalent result.

  In a second embodiment, visible in FIG. 9, the decision module 43 has two branches. A first branch comprises a low-pass filter 45 for smoothing the phase signal. The cutoff frequency duf of the low-pass filter 45 is, for example, less than 1 kHz, so that the signal at the output of the low-pass filter 45 is a so-called continuous phase signal (D, which does not fluctuate over a period of time). very large before the period TBF of the low frequency carrier wave 27. The continuous phase signal qDc is sent to a first signal comparator 46 with a predetermined threshold e, said continuous threshold.The signal comparator element 46 is suitable to deliver a characteristic signal 47 when the value of the continuous phase signal q> c is greater than or equal to the continuous threshold e, and to deliver no signal when the value of the

  continuous phase signal qDc is below the continuous threshold e.

  In the second embodiment, the decision module 43 comprises, in parallel with the first branch, a second branch with a high-pass filter 52 for detecting the fluctuating phase signal Qf. The cut-off frequency f 2 of the high-pass filter 52 is, for example, less than 10 kHz, to select the fluctuating component (f and eliminate the DC component C. The high-pass filter 52 is connected to an amplifier 53 to amplify the phase signal fluctuating (> f, then to a second signal comparator element 54, able to deliver a characteristic signal 57 when the absolute value of the fluctuating phase signal of is greater than or equal to a fluctuation threshold e, and not provide no signal when the absolute value of the fluctuating phase signal (If is less than the fluctuation threshold ú) To be simultaneously responsive to the existence of the continuous phase signal (ID and the fluctuating phase signal (f, the decision module 43 comprises a non-exclusive OR logic gate 55, connected in input to the two signal comparator elements 46 and 54, and able to output the cancellation signal An to the microcontroller 20 when it receives the characteristic signal 47 and / or

the characteristic signal 57.

  In FIG. 10, the curve 60 represents the evolution of the absolute value of the fluctuating component (If as a function of time over several modulation periods Tm during normal use of the system. modulation bm of value 1, the corresponding phase jump is reflected on the reference signal 41

  with the operational delay Dr and on the signal 42 with the delay P + Q + R.

  Thus, the fluctuating phase signal (If has a succession of slots 61 of time width substantially equal to the time of

  P propagation, a few nanoseconds.

  In FIG. 11, the curve 62 represents the evolution of the absolute value of the fluctuating component (I) f as a function of time over several modulation periods Tm, during an attempted piracy by relay boxes. In this case, each phase jump is reflected on the signal 42 with the delay At + Q + R. Thus, the fluctuating phase signal (tIf in this case has a succession of slots 63 of time width substantially equal to the transmission delay Δt, that is

the order of a few microseconds.

  As shown in FIG. 10, during normal use of the system according to the invention in the second embodiment, a fluctuating component (non-zero 1f is also observed, but it has a very short characteristic time, of the order The integral of the fluctuating component (I) f over a modulation period Tm therefore has a value of at least a factor of at least 100 in the case of normal use of the system compared to the case of an attempt In order to avoid the emission of the cancellation signal An in response to this fluctuation of very short characteristic time, and to limit the sensitivity to noise of the system according to the invention, the second signal comparator element 54 is preferably , capable of integrating the fluctuating phase signal (If over an integration time Ti longer than the modulation period Tm and of comparing said fluctuating phase signal (Of with the threshold of uctuation after this integration. For example, the integration time Ti is of the order of 50 to 100 times Tm. The duration of integration

  Ti is of course less than the total duration of the bidirectional dialogue.

  Thus, to summarize, the decision module 43 of the second embodiment is able to deliver the cancellation signal An in the event of an attempt to pirate using relay boxes, excluding the case of normal use. of the system according to the invention, in two complementary ways: - either by detecting a continuous component (Oc greater than the continuous threshold e, when the transmission delay At is substantially different from an integer N greater than or equal to 1 of periods TBF or by detecting a fluctuating component Of of integrated amplitude greater than the fluctuation threshold c, especially when the transmission delay At is substantially equal to an integer N greater than

equal to 1 of TBF periods.

  As a variant, with the second embodiment of the decision module 43, the operational delay Dr can be chosen to be zero, in order to limit the cost of the system for example. In this case, the continuous phase signal Oc has a non-zero reference value 9o substantially equal to (po = 2n (R + Q) / TBF during normal use of the system The continuous threshold e of the first signal comparator 46 is then chosen to be greater than the reference value q 0. In this case, the fluctuating phase signal (Of, during normal use and an attempted hacking, has a characteristic elongated fluctuation time substantially of R + Q The second comparator element 54 is then designed to discriminate from one another the generally normal width cranial signal R + Q + P, obtained in normal use, of the typical width signal R + Q + At, which would be obtained during an attempted hack.In this variant, the

  modulation period Tm is chosen greater than the delay R + Q.

  The microcontroller 20 is able to inactivate the transmission of the activation command 38 as soon as it receives the cancellation signal An. For example, the microcontroller 20 is able to interrupt the current communication protocol before the data of the signal If necessary to issue the order 38 have been received by the central unit 1 and / or to prohibit the issuance of the order 38 during a period of prohibition

  determined from the reception of the cancellation signal An.

  In an alternative embodiment of the identification device I, the fitness module 31 is connected to the second microcontroller 30, as can be seen in FIG. 12. In this variant, the crenellated signal 64 is sent to a demodulator 87 in the fitness module 31 for recovering the modulation bits bm. The demodulator 87 includes a clock recovery module 79 for recovering a signal 83 conforming to the carrier wave 27 at 125 kHz and an exclusive OR gate 80. The signal 83 and the slot signal 64 are sent to the input of the exclusive OR gate. 80, for outputting a square wave signal 81 representing the modulation bit sequence bm

  having served to modulate the wave 27 at its emission.

  The second microcontroller 30 is able to use the signal 81 to generate, according to a predetermined algorithm known to the unit

  1, an alteration signal 82 for altering the square-wave signal 64.

  The tamper signal 82 is inputted to a second exclusive OR gate 88 of the fitness module 31. At the second input of the second exclusive OR gate 88 is sent a crimped signal 64 ', which is generated by a frequency divider 78 of the fitness module 31. The crenellated signal 64 'represents the transitions of the square wave signal 64 at a frequency f0' equal to a fraction of the fundamental frequency fo. The frequency divider 78 makes it possible to limit the band

  passing necessary for the transport of the signal 34 to the central unit 1.

  The phase signal 34 is finally obtained at the output of the second gate

Exclusive OR 88.

  In this variant embodiment, the signal 34 represents the transitions of the carrier wave 27 with its phase jumps introduced by the generator 24, at a possibly reduced frequency, and with the alterations introduced by the second microcontroller 30. For example, the second microcontroller 30 can, with the aid of the alteration signal 82, reverse for a predetermined period the phase of the signal 34 relative to

to that of signal 64.

  Thus, in FIG. 13, the phase signal (q at the input of the comparator module 66 during a period of several modulation periods Tm is represented as a function of time. The curve 84 represents the voltage signal Vm corresponding to a random sequence of modulation bits bm During normal operation of the control system, the phase signal (D is in accordance with that represented by curve 85 and exhibits a low amplitude oscillation following each transmission of a value modulation bit 1, as previously explained In the embodiment described above, the second microcontroller 30 can introduce a phase inversion in the signal 34 at time t1, which causes a phase opposition between the signals 41 and 42 compared by the phase comparator 40. The phase signal (I then takes a maximum value, as represented by the curve 86, until the second microcontroller 30 introduces a second signal. phase inversion me that will return the phase signal (at its minimum value. In this variant, the decision module 43 is able to recognize the alterations introduced by the microcontroller 20 according to a predetermined algorithm and as a function of the bit sequence bm received, so as not to trigger the cancellation signal An when such a alteration causes the momentary crossing of the threshold E by the phase signal (Q. The introduction by the second microcontroller 30 of alterations of the phase signal 34 makes it possible to defeat a possible hacking attempt with the aid of a simple repeater signal that retransmits to the vehicle V a signal identical to the signal Si sent by it to the identification device I. Although the invention has been described in connection with several particular embodiments, it is obvious that it is in no way limited and includes all the technical equivalents of the means described and their combinations, if they fall within

the scope of the invention.

Claims (18)

  1. A remote control method for controlling a member (O) of a motor vehicle (V), in particular means for locking the access to said vehicle and / or means for starting said vehicle, consisting in setting up a bidirectional dialogue by radio transmission between a central unit (1) carried by said vehicle (V) and a portable identification device (I) intended to be worn by a user (U), said dialogue comprising at least a first communication, continuous or interrupted a first signal (S1) transmitted from a first transmitter (2, 24) of said central unit (1) to a first receiver (3) of said identification device (I) and a second communication, whether continuous or interrupted, a second signal (S2) transmitted from a second transmitter (4) of said identification device (I) to a second receiver (5) of said central unit (1), said dialogue being able to be established only. if the distance separating said central unit (1) from said identification device (I) is substantially less than a predetermined communication distance (d), said method being characterized by comprising the steps of: (i) triggering said first communication, said first signal (SI) being carried by a first carrier wave (27); (ii) triggering said second communication, said second communication being at least partially conducted while said first communication continues, said second signal (S2) comprising an identification signal (Si) of said identification device and a signal of said image phase (34), representing the phase of said first carrier wave (27) received by said identification device, (iii) the emission of an activation command (38) for activating said member (O) after receiving said identification signal (Si) by said central unit (1); said method also comprises, simultaneously with said first and second communications, a step of successive comparisons between the current value of the phase represented by said image phase signal (42) received by said second receiver (5) and the current value of the phase a reference signal (41) conforming to the carrier wave (27) being transmitted by said first transmitter (2,24) delayed by a predetermined reference delay (Dr), zero or non-zero, the phase represented by said image phase signal (42) having, during the comparisons step, a transmission delay with respect to the phase of said carrier wave (27) being transmitted by said first transmitter (2, 24), said activation order transmission (38) being prohibited as soon as the result of said successive comparisons ()) fills a   predetermined cancellation criterion.   2. Method according to claim 1, characterized in that the phase of said first carrier wave (27) undergoes a   random modulation during the duration of its emission.   3. Method according to claim 2, characterized in that said random modulation comprises the introduction of phase jumps in said first carrier wave (27) at successive random instants at irregular intervals greater than or equal to one period.   of predetermined modulation (T ,,).   4. Method according to claim 3, characterized in that said modulation period (TmT) is substantially greater than the period (TBF) of said first carrier wave (27); preferably of the order of 5 to 10 times the period (TBF) of said first carrier wave (27).   5. Method according to one of claims 3 or 4,   characterized by the fact that the amplitude of said phase jump (5 (p) is substantially fixed.   6. Method according to claim 5, characterized in that the ratio between said amplitude (& (p) and said modulation period (Tm) is significantly lower than the fundamental frequency (f0) of said first carrier wave (27), preferably less than 1 / 5th of this fundamental frequency (f0).   7. Method according to one of claims 3 to 6,   characterized in that the phase represented by said image phase signal (42) has, with respect to the phase of said carrier wave (27), alterations introduced by the identification device (I) as a function of said phase jumps according to a predetermined algorithm known to said central unit (1).   8. Method according to one of claims 1 to 7,   characterized by the fact that, said transmission delay being dependent on the time required for the path of said first signal (S1) between said central unit (1) and said identification device (I) and the time required for the path of said second signal (S2 ) between said identification device (I) and said central unit (1), said reference delay (Dr) is chosen substantially equal to a predetermined normal delay (R + Q), said normal delay (R + Q) being substantially the fixed value of said transmission delay when the distance separating said central unit (1) from said identification device (I) is substantially less than said distance   predetermined communication (dj).   9. Method according to one of claims 1 to 8,   characterized by the fact that said cancellation criterion is validated if the difference between said two compared phase values (I) exceeds a level predetermined maximum (E).   10. Method according to one of claims 2 to 9,   characterized in that the difference between said two compared phase values (I) comprises the sum of a so-called continuous component (Ic), substantially constant over a duration greater than said modulation period (Tm), and a fluctuating component (If) over the duration of said modulation period (Tm), said cancellation criterion being validated as soon as the absolute value of said DC component (> c) exceeds a first predetermined threshold (_).   11. Method according to claim 10, characterized in that said cancellation criterion is validated as soon as the integral of the amplitude of said fluctuating component ('f) over a predetermined integration time (Ti) exceeds a second predetermined threshold (E).   12. System for implementing the method according to claim 1, comprising said central unit (1) and said portable identification device (I), characterized in that said central unit (1) comprises a first microcontroller (20). ) connected to said member (0) for delivering said activation command (38), said first radiofrequency transmitter (2,24) linked to said first microcontroller (20) for transmitting said first carrier wave (27) and said first signal (IF ), said second radio frequency receiver (5) for receiving said second signal (S2), a phase comparator module (40) linked to said second receiver (5) and said first transmitter (2,24) for performing said successive comparisons, a decision module (43) linked to said phase comparator module (40) for receiving the result of said comparisons (<) and linked to said first microcontroller (20) to deliver a cancellation signal (An) thereof activation (3 8) as soon as the said cancellation criterion is validated; said identification device (I) comprising said first radio frequency receiver (3) for receiving said first signal (SI), a second microcontroller (30) for generating said identification signal (Si), said second radio frequency transmitter (5) for transmitting said second signal (S2), said second transmitter (5) being coupled to said first receiver (3) for receiving said image phase signal (34) and said second microcontroller   (30) for receiving said identification signal (Si).   13. System according to claim 12, characterized in that said system is also for implementing the method according to claim 2, said central unit (1) comprising a random signal sequence generator (39) linked to said first transmitter (2,24) for modulating the phase of said first carrier wave (27) during its transmission. 14. System according to claim 13, characterized in that said system is also for implementing the method according to claim 3, said random signal sequence generator (39) being able to deliver periodically to said first transmitter ( 2) a random binary signal (bm), said first transmitter (2,24) being able to introduce a phase jump in said first carrier wave (27) each time said received binary signal (bi) takes a value predetermined.   15. System according to claim 14, characterized in that said system is also for implementing the method according to claim 7, said identification device (I) comprising a demodulator (87) linked to the first receiver (3). receiving said first carrier wave (27) and the second microcontroller (30) to deliver said demodulated random bit signal (bin) of said first carrier wave (27); said second microcontroller (30) being adapted to modify said image phase signal (34) according to said binary signal random (bm).   16. System according to one of claims 12 to 15,   characterized in that said system is also for carrying out the method according to claim 9, said decision module (43) comprising a low-pass filter (65) whose input is connected to the output of said comparator module of phase (40) and whose output is connected to a signal comparator (66) for comparing the difference between said two compared phase values (D) with said predetermined maximum level (E). 17. System according to claim 16, characterized in that said system is also for implementing the method according to claim 11, said decision module (43) comprising a high-pass filter (52) whose input is connected to the output of said phase comparator module (40) for extracting said fluctuating component ('f) from said comparison result (<) and whose output is connected to a second comparator (54), distinct or otherwise from the signal comparator ( 66), for comparing said fluctuating component (Df) with said second threshold predetermined (ú).   18. System according to one of claims 12 to 17,   characterized in that said first transmitter (2,24) is adapted to transmit said first signal (SI) by amplitude modulation or phase modulation.   said first carrier wave (27).