Countermeasure method against man-in-the-middle attacks in the UWB protocol

Abstract

The invention relates to a method for countering an attack aimed at disrupting a distance measurement obtained by measuring signal transmission times between transmitter / receiver devices (TX, RX) of UWB type signals, the method comprising steps consisting in: carrying out a first distance measurement (DTU) by measuring transmission times between first communication interfaces (TX1, RX1) of UWB type, of the transmitter / receiver devices; carrying out a second distance measurement (DTB1) between the transmitter / receiver devices, by second communication interfaces (TX2, RX2) of a type distinct from UWB, of the transmitter / receiver devices; and only if a difference between the first and second distance measurements is less than a first threshold value, activating or not an operation, depending on a comparison of the first distance measurement with a second threshold value (TH). Figure 1

Description

Title of the invention: Method of countermeasure against man-in-the-middle attacks in the context of the UWB protocol Technical field

[0001] The present invention relates to the UWB ("Ultra Wide Band") protocol implemented to evaluate a transmission distance on the basis of the transmission time of messages exchanged between two transmitter / receiver devices. In particular, the present invention aims to counter intermediary or "man-in-the-middle" attacks aimed at disrupting transmissions between two transmitter / receiver devices, in order to distort the evaluation of the distance between these two devices. State of the art

[0002] Many applications implement the UWB protocol to accurately and reliably assess a distance based on a message transmission time between transmitter / receiver devices. This is the case, for example, of a "hands-free" vehicle door opening application for unlocking the vehicle door when the key is detected at a distance less than a threshold value, typically one to two meters. Thus, the user does not need to take the key in his hand to press an opening trigger button on the key, and can therefore leave the key in his pocket. Furthermore, some smartphones are equipped with a UWB interface that can be used by an application installed in the smartphone to act as a "hands-free" key.

[0003] To obtain a distance evaluation with an accuracy of less than one meter, using the UWB protocol, it is necessary to take into account multi-path propagation. Indeed, under the effect of multi-path propagation, the receiver of a message receives several copies of the transmitted message which can be distorted and attenuated. Each of these copies is shifted in time according to the propagation time in the path taken by the copy. Thus, the spread of the propagation times of the copies can correspond to several meters of difference. To obtain the required accuracy, the receiver must determine the arrival time of the first copy received. This task proves to be particularly difficult, especially when obstacles are present between the transmitter and the receiver.

[0004] An attacker located between the transmitter and the receiver can deceive the latter by sending a message configured to be perceived as the first copy of a message sent by an authentic transmitter. Thus, an attacker can, for example, open the door of a vehicle parked in front of a room where the owner of the vehicle is located.

[0005] The IR-UWB ("Impulse Radio" - UWB) protocol based on the transmission of very narrow pulses makes it possible to improve the accuracy of the distance measurement by facilitating the detection of the first copy of the transmitted message. However, this protocol does not make it possible to completely counter intermediate attacks, but simply to limit the alteration of the evaluated distance, resulting from the attack to the period of reception of all the copies produced by the multi-path transmission.

[0006] Distance Bounding protocols introduce cryptographic mechanisms. However, these protocols do not apply to the physical PHY layer which is affected by the type of attack previously described.

[0007] It is therefore desirable to propose a method for countering intermediate attacks within the framework of the UWB protocol applied to the measurement of distance between two transmitter / receiver devices. Summary

[0008] Embodiments relate to a method of countermeasuring an attack aimed at disrupting a distance measurement obtained by measuring signal transmission times between first and second "Ultra Wide Band" - UWB signal transmitter / receiver devices, the method comprising steps consisting of: carrying out a first distance measurement separating the first and second transmitter / receiver devices, by the first transmitter / receiver device, by measuring transmission times between first UWB type communication interfaces, belonging respectively to the first and second transmitter / receiver devices;performing a second distance measurement separating the first and second transmitter / receiver devices, in the first transmitter / receiver device, by second communication interfaces belonging respectively to the first and second transmitter / receiver devices, the second communication interfaces being of a type distinct from UWB; performing a first comparison of the first and second distance measurements; if a difference between the first and second distance measurements is less than a first threshold value, activating or not a first operation by the first transmitter / receiver device, depending on the result of a second comparison consisting of comparing the first distance measurement with a second threshold value;and if a difference between the first and second distance measurements is greater than the threshold value, not activating the first operation, the second distance measurement being carried out by measuring transmission times between the second communication interfaces, the second communication interfaces being of the Bluetooth Low Energy -BLE type, the two devices carrying out the first and second distance measurements and carrying out the first comparison, the second transmitter / receiver device activating a second operation if the difference between the first and second measurements of; distance is greater than the first threshold value, the first distance measurement being calculated using a first measurement of duration between a time of transmission of a query message and a time of reception of a response message, by one of the first communication interfaces of the first and second transmitter / receiver devices, and a second measurement of a duration between a time of reception of the query message and a time of transmission of the response message, by the other of the first communication interfaces of the first and second transmitter / receiver devices, the first distance measurement being further calculated using a third measurement of duration between the time of reception of the response message and a time of transmission of a second query message, by one of the first communication interfaces of the first and second transmitter / receiver devices,and a measurement of a duration between the time of transmission of the first response message and a time of reception of the second interrogation message by the other of the first communication interfaces of the first and second transmitter / receiver devices.

[0009] Thus, by using two separate communication channels, it is possible to obtain two distance measurements and to compare the obtained measurements. Since it is less likely that an attacker can disrupt both measurements simultaneously, such an attack can be detected by a simple comparison of the two distance measurements. The implementation of this countermeasure proves to be particularly simple since devices integrating a UWB type communication interface generally include another communication interface.

[0010] According to one embodiment, the first operation comprises a door unlocking and is activated if the difference between the first and second distance measurements is less than the first threshold value, and if the first distance measurement is less than a second threshold value.

[0011] According to one embodiment, the first operation comprises a door locking and is activated if the difference between the first and second distance measurements is greater than the first threshold value, or if the first distance measurement is greater than a second threshold value.

[0012] Embodiments may also relate to a system comprising first and second transmitter / receiver devices, each of the first and second transmitter / receiver devices comprising: a first communication interface of UWB type, and a second communication interface of a type distinct from UWB, the system being configured to implement the method previously defined. Brief description of the figures

[0013] The present invention will be better understood with the aid of the following description of exemplary embodiments with reference to the appended figures, in which identical reference signs correspond to structurally and / or functionally identical or similar elements.

[0014] [Fig.l] Figure 1 schematically represents two transmitter / receiver devices exchanging distance measurement messages, for example according to the UWB protocol,

[0015] [Fig.2] Figures 2A and 2B schematically represent steps of distance measurement methods, according to the UWB protocol,

[0016] [Fig.3] Figure 3 shows steps of a distance measurement method including countermeasurement steps, according to one embodiment. Detailed description

[0017] Figure 1 shows two transmitter / receiver devices TX, RX exchanging distance measurement messages according to the UWB protocol. The TX device is located at a distance DT from the RX device. The TX device is configured to take the initiative to trigger a distance measurement with the RX device. The RX device is configured to trigger an operation, for example a security operation such as unlocking or opening a door if the measured distance between the TX and RX devices is less than a distance threshold value TH.

[0018] In an attack configuration presented in FIG. 1, the TX device exchanges position measurement messages with the RX device. Thus, the RX device evaluates the distance DT which separates it from the RX device. An attacker equipped with a transmitter device AX positions itself at a distance DA from the RX device, less than the threshold value TH and emits signals capable of disrupting the messages received by the RX device. The signals emitted by the attacker's AX device are configured to distort the distance evaluated by the RX device, so that this distance corresponds to the distance DA with the AX device. The attacker can thus trigger the action executed by the RX device by positioning itself at a distance DA less than the threshold value TH. For this purpose, the AX device can be configured to exploit the multi-path processing of the received signals, executed by the RX device.

[0019] Note that the action executed by the RX device can also be a door locking when the distance DL with the TX device is greater than a second threshold value. In this case, the attacker can aim to prevent this action by positioning the AX device sufficiently close to the RX device so that the distance measured by the RX device remains less than this second threshold value.

[0020] Figures 2A, 2B illustrate SS-TWR ("Single Sided - Two Way Ranging") and DS-TWR ("Double Sided - Two Way Ranging") distance evaluation methods TFM1, TFM2 that can be used to measure the distance DT between the devices TX and RX. In the evaluation method TFM1 illustrated in FIG. 2A, the TX device sends a distance measurement request message M1 to the RX device, and the RX device sends a distance measurement response message M2 to the TX device in response. The distance DT between the TX and RX devices can thus be evaluated by the following equation:

[0021] DT = C.(T1'- Tl) / 2, (1)

[0022] in which Tl is the time elapsed between the instant of reception of the message Ml by the RX device and the instant of transmission of the message M2 by the RX device, Tl' is the time elapsed between the instant of transmission of the message Ml by the TX device and the instant of reception of the message M2 by the TX device, and C is the speed of propagation of electromagnetic waves in the air. The time of flight (Tl' - Tl) / 2 (= (TOFl+TOF2) / 2) corresponds to the average of the transmission time TOF1 of the message Ml and the transmission time TOF2 of the message M2 between the TX and RX devices. The duration Tl' can be transmitted by the TX device to the RX device in an MD message following the message M2.

[0023] In the DS-TWR evaluation method TFM2 of FIG. 2B, the TX device sends the distance measurement request message M1 to the RX device, the RX device sends the distance measurement response message M2 to the TX device in response, and the TX device sends a distance measurement response message M3 to the RX device in response. The distance DT between the TX and RX devices can be evaluated by the following equation:

[0024] DT = C.(T1'.T2' - T1.T2) / (2.(T1+T2+T1'+T2')), (2)

[0025] in which Tl is the time elapsed between the time of reception of the message Ml by the RX device and the time of transmission of the message M2 by the RX device, Tl' is the time elapsed between the time of transmission of the message Ml by the TX device and the time of reception of the message M2 by the TX device, T2 is the time elapsed between the time of reception of the message M2 by the TX device and the time of transmission of the message M3 by the TX device, and T2' is the time elapsed between the time of transmission of the message M2 by the RX device and the time of reception of the message M3 by the RX device. The times Tl' and T2 can be transmitted by the TX device to the RX device in the message M3 or in a following message MD'.

[0026] Once the distance DT is evaluated, the RX device can compare the distance DT to a threshold value TH and trigger an action based on the result of the comparison.

[0027] It should be observed that in Figures 2A, 2B, the roles of the TX and RX devices can be reversed, and the TX device can finally evaluate the distance DT and transmit it to the RX device.

[0028] Furthermore, the distance measurement DT can be obtained from the duration measurements Tl, Tl', T2, T2' by different equations. For example, the distance measurement can be obtained by calculating the average of distances obtained using equation (1) applied on the one hand to the duration measurements Tl and Tl', and on the other hand to the duration measurements T2 and T2'.

[0029] Figure 3 represents steps S1 to S26 of a remote control method as a function of the distance between a device triggering a command, namely the transmitter / receiver device TX and a device executing the command, namely the device RX. The devices TX, RX each comprise a first communication interface TX1, RX1 of UWB type, and a second communication interface TX2, RX2, for example of BLE ("Bluetooth Low Energy") or WiFi™ type. The communication interfaces of BLE or WiFi™ type have the advantage of being able to remain active or on standby without excessive power consumption, which is not the case for communication interfaces of UWB type. It may therefore be advantageous for the first interface RX2 to be inactive outside of periods when it is not necessary to measure the distance DT with the device TX.

[0030] In step S1, the TX device controls the transmission of a wake-up message WK by its second communication interface TX2. In the following step S2, the TX device activates its first communication interface TX1. In step S3, the WK message is transmitted by the second communication interface TX2 of the TX device to the second communication interface RX2 of the RX device. In step S4, the second communication interface RX2 transmits the wake-up message WK to the RX device which activates its first communication interface RX1, in step S5. In step S6, the activation of the first communication interface RX1 triggers the transmission of a message AK for activating a distance evaluation method. The AK message is received by the first communication interface TX1 of the TX device. In step S7, the first communication interface TX1 activates the TFM evaluation method which can be the TFM1 or TFM2 method previously described.At the end of the execution of the TFM evaluation method by the communication interface TX1, in steps S8 and S9, the first communication interface TX1 transmits to the device TX and to the first communication interface RX1, the time of flight measurement T1' and possibly the time of flight measurement T2, according to the TFM1 or TFM2 evaluation method executed.

[0031] In step S10, at the end of the execution of the TFM evaluation method by the first communication interface RX1, the latter transmits to the RX device the flight time measurement T1 and possibly the flight time measurement T2', according to the TFM1 or TFM2 evaluation method executed. In step S11, the flight times T1', T2 received by the first communication interface RX1 are transmitted to the RX device. In step S12, the RX device records the current time and stores it in a timestamp data ("timestamp") TS1. In step S13, the timestamp data TS1, and possibly the flight time T1 and the flight time T2' are transmitted to the second communication interface RX2. In step S14, the second communication interface RX2 transmits the timestamp data TS1, and possibly the flight time T1, and the flight time T2' to the second communication interface TX2 of the TX device. In step S15, the second communication interface TX2 transmits the received data (TS1, T1, T2') to the TX device. In step S16, the TX device records the current time and stores it in a timestamp data TS2. In steps S17, S18 and S19, the timestamp data TS2 is transmitted to the RX device, via the second interfaces TX2 and RX2. Upon receipt of the timestamp data TS2, in step S20, the RX device records the current time and stores it in a timestamp data TS3.Then, the RX device calculates a distance DTB1 based on the timestamp data TS2 and TS3, and calculates a distance DTU based on the flight times Tl' and possibly T2 received and the flight times Tl and possibly T2' measured and provided by the first communication interface RX1.

[0032] In step S21, the RX device compares the distances DTU and DTB1. The RX device executes step S22 if the distances DTB2 and DTU have a non-significant difference, for example less than a first threshold value, otherwise it executes step S23. In step S22, the RX device executes an operation CM1 according to the distance measurement DTU which is then judged to be correct. This operation may consist of comparing the distance measurement DTU with a second distance threshold value and executing a command, for example unlocking a door, if the distance measurement DTU is less than the distance threshold value. Step S23 may comprise the execution of another command CM2 and possibly the emission of an alarm signal.

[0033] In the example where the command CM1 is a door unlocking, the command CM2 may comprise the locking of the door.

[0034] Following step S18, the device TX can execute steps S24 to S26 for verifying measured distances. In step S24, the device TX in turn calculates the distance DTU as a function of the flight times T1 and possibly T2' received and the flight times T1' and possibly T2 measured and supplied by the first communication interface TX1, and calculates a distance DTB2 as a function of the time stamp data TS1 and TS2. In step S25, the device TX compares the distances DTB2 and DTU, and emits an alarm signal in step S26 if the distances DTB2 and DTU have a significant difference, for example greater than the first threshold value.

[0035] The first threshold value and the comparison mode implemented in steps S21 and S25 are determined so as to take into account the differences in precision of the distance measurements obtained by the flight time calculations of the transmissions between the first interfaces TX1, RX1 and between the second interfaces TX2, RX2. Indeed, a distance calculation from the flight time of a BLE transmission for example (of the order of a meter) is much less precise than a distance calculation from the flight time of a UWB transmission (of the order of 10 cm).

[0036] If the second communication interfaces TX2, RX2 have the capability, they can directly read the timestamp data TS1, TS2, TS3. Thus, it is possible to reduce the latency times between the time of reading each timestamp data and the time to be timestamped of transmission or reception of the message, and therefore the accuracy of the timestamp.

[0037] In a simplified version, the timestamp data TS3 is not recorded, and the distance DTB1 is calculated by the device RX in step S20, as a function of the timestamp data TS1 and TS2.

[0038] Thanks to these provisions, it is possible to detect an attack on the transmissions between the first interfaces TX1 and RX1, aimed at disrupting the distance measurement between the devices TX and RX. Indeed, for such an attack to be carried out successfully, the attacker would also have to disrupt the transmissions between the second interfaces TX2 and RX2 and this disruption would have to lead to a disrupted distance measurement close to the disrupted distance measurement determined using the transmissions between the first interfaces TX1, RX1.

[0039] It will be clear to those skilled in the art that the present invention is susceptible to various variant embodiments and various applications. In particular, the invention is not limited to the measurement of the distance between the TX and RX devices by measuring flight times using the second communication interfaces TX2, RX2. Indeed, this second distance measurement can be carried out by any other means sufficiently precise to allow validation of the first distance measurement obtained by the flight times measured by the first communication interfaces TX1, RX1. For example, one of the TX, RX devices can be fixed and have a precisely known position. The other of the devices can determine its position by any means, for example using a satellite geographic positioning system.

[0040] The invention can be applied to the control of operations such as the opening and locking of a door such as a vehicle door or a room door, the opening of a barrier for example for access to parking lots. The invention can also be applied to validation operations for example of a payment by mobile phone, or even of a concert or public transport ticket. The invention can also be applied to access operations for example to a personal device such as a personal computer or tablet, or to activate devices such as household appliances.

Claims

1. Claims 1. Method of countermeasure against an attack aimed at disrupting a distance measurement obtained by measuring signal transmission times between first and second transmitter / receiver devices (TX, RX) of "Ultra Wide Band" - UWB type signals, the method comprising steps consisting of: carrying out a first distance measurement (DTU) separating the first and second transmitter / receiver devices, by the first transmitter / receiver device (RX), by measuring transmission times between first communication interfaces (TX1, RX1) of UWB type, belonging respectively to the first and second transmitter / receiver devices; performing a second distance measurement (DTB1) separating the first and second transmitter / receiver devices, in the first transmitter / receiver device, by second communication interfaces (TX2, RX2) belonging respectively to the first and second transmitter / receiver devices, the second communication interfaces being of a type distinct from UWB; performing a first comparison of the first and second distance measurements; if a difference between the first and second distance measurements is less than a first threshold value, activating or not a first operation by the first transmitter / receiver device, depending on the result of a second comparison consisting of comparing the first distance measurement to a second threshold value (TH);and if a difference between the first and second distance measurements is greater than the threshold value, not activating the first operation, the second distance measurement being carried out by measuring transmission times between the second communication interfaces (TX2, RX2), the second communication interfaces (TX2, RX2) being of the Bluetooth Low Energy - BLE type, the two devices (TX, RX) carrying out the first and second distance measurements (DTU, DTB1, DTB2) and carrying out the first comparison, the second transmitter / receiver device activating a second operation (AL) if the difference between the first and second distance measurements is greater than the first threshold value, the first distance measurement being calculated using a first measurement of; duration (TT) between a time of transmission of an interrogation message (Ml) and a time of reception of a response message (M2), by one of the first communication interfaces of the first and second transmitter / receiver devices (TX, RX), and a second measurement of a duration (Tl) between a time of reception of the interrogation message and a time of transmission of the response message, by the other of the first communication interfaces of the first and second transmitter / receiver devices, the first distance measurement being further calculated using a third measurement of duration (T2) between the time of reception of the response message (M2) and a time of transmission of a second interrogation message (M3), by one of the first communication interfaces of the first and second transmitter / receiver devices (TX, RX),and a measurement of a duration (T2') between the time of transmission of the first response message and a time of reception of the second interrogation message by the other of the first communication interfaces of the first and second transmitter / receiver devices.,

2. 2. The method of claim 1, wherein the first operation comprises door unlocking and is activated if the difference between the first and second distance measurements is less than the first threshold value, and if the first distance measurement is less than a second threshold value.

3. 3. Method according to one of claims 1 or 2, in which the first operation comprises a door locking and is activated if the difference between the first and second distance measurements is greater than the first threshold value, or if the first distance measurement is greater than a second threshold value.

4. 4. System comprising first and second transmitter / receiver devices (TX, RX), each of the first and second transmitter / receiver devices comprising: a first communication interface (RX1, TX1) of UWB type, and a second communication interface (RX1, TX1) of a type distinct from UWB, the system being configured to implement the method according to one of claims 1 to 3.

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