A safety ranging method based on dynamic response signals

Abstract

The application discloses a kind of security ranging methods based on dynamic response signal, comprising the following steps: verifier generates ranging signal and sends to responder;Responder generates response signal after fixed delay processing time after detecting the arrival of ranging signal, and then sends to verifier, wherein, verifier controls the generation of response signal using encrypted payload data in ranging signal, responder decrypts encrypted payload data using initial key shared with verifier, and generates response signal according to decrypted data;Verifier calculates the distance between verifier and responder according to round-trip delay processing time and the delay processing time of responder after detecting the arrival time of response signal, which can realize security ranging.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of wireless communication, and relates to a safety ranging method based on a dynamic response signal. BACKGROUND

[0002] Ultra Wide Band (UWB) technology has the advantages of large channel capacity, fast transmission rate, strong anti-multipath ability, high resolution, low transmission power, and small system power consumption, so that the UWB-based ranging technology has been widely applied at present: the UWB chip for measuring distance has been massively deployed in smart phones, cars and other products, and its applications involve many scenes such as keyless entry and start of cars, mobile payment, space perception and indoor positioning.

[0003] In 2002, the Federal Communications Commission (FCC) approved that UWB technology can be applied to civilian communication systems, and gave two definitions of UWB signals: a signal with an absolute bandwidth greater than or equal to 500MHz or a relative bandwidth less than or equal to 0.2 is considered as a UWB signal. Let the absolute bandwidth of the signal be B:

[0004] B=f H -f L

[0005] In the formula, f H and f L are the high-end frequency and low-end frequency corresponding to the power spectral density decay of the signal by 10dB respectively. The relative bandwidth B frac can be expressed as:

[0006]

[0007] In the formula, f c is the center frequency of the signal:

[0008]

[0009] In addition, the FCC also stipulates that the working frequency band of UWB should be between 3.1GHz and 10.6GHz, and limits the signal power to below-41.3dBm / MHz to avoid interference with other communication signals in the same working frequency band.

[0010] At present, there are various implementations of UWB signals, among which the most widely used is pulse radio. Pulse radio technology refers to a radio technology that uses narrow pulses with a very low duty cycle as a carrier to realize information transmission. The UWB signal generated based on pulse radio technology includes Gaussian pulses and Butterworth pulses, etc.

[0011] Nowadays, malicious attackers can launch distance reduction attacks on the ranging process from the physical layer, causing the ranging device to mistakenly believe that the target user is within a sufficiently close range. Such attacks can lead to incidents that endanger people's property security, such as car theft and unauthorized payments. Therefore, it is necessary to ensure that legitimate ranging devices can still achieve secure ranging even when attackers are present during the ranging process, from the physical layer perspective. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of the prior art and provide a safe ranging method based on dynamic response signals, which can achieve safe ranging.

[0013] To achieve the above objectives, the safe ranging method based on dynamic response signals described in this invention includes the following steps:

[0014] The verifier generates a ranging signal and sends it to the responder;

[0015] After detecting the arrival of the ranging signal, the responder generates a response signal after a fixed delay and sends it to the verifier. The verifier uses the encrypted payload data in the ranging signal to control the generation of the response signal. The responder uses the initial key shared with the verifier to decrypt the encrypted payload data and generates the response signal based on the decrypted data.

[0016] After detecting the arrival time of the response signal, the verifier calculates the distance between the verifier and the responder based on the round-trip delay processing time and the responder's delay processing time.

[0017] Before initiating each ranging process, the verifier first generates a dynamic key (key) to encrypt the payload data in the next ranging frame. n And a random number seed, then the SHA-256 algorithm is used to map key1 to an AES key, and the plaintext sequence is encrypted using the AES-256 algorithm to obtain the encrypted data D = (D1, D2, ..., D) to be placed in the payload for transmission. 256 );

[0018] The ranging signal s(t) generated after modulation of the ranging frame is:

[0019]

[0020] s(t)=P(t)+STS(tT g )+D(tT g -T t )

[0021] Among them, D k Let p(t) be the k-th bit of the load sequence, and T be the pulse signal.p T is the duration of the pulse signal s P(t) is the synchronization signal, STS(t) is the modulated STS signal, T g T is the duration of the synchronization signal t T is the duration of the STS signal.

[0022] The ranging signal y R (t) is:

[0023] y R (t) = s(t) * h VR (t) + n(t).

[0024] The response signal x R (t) is:

[0025] x R (t) = g(t) + a1g(t - b1T d ) + a2g(t - b2T d )

[0026] where T d is the maximum relative displacement time, g(t) is the base signal, a = (a1, a2) and b = (b1, b2) are two sets of random numbers generated by the responder using the random number seed extracted from the received load data to control the structure of the response signal, a k ∈ [0.5, 2], b k ∈ [0, 1] and b1< b2.

[0027] The base signal g(t) is:

[0028]

[0029] where TM R (t) is the timing signal extracted by the responder from the ranging signal.

[0030] The timing signal TM R (t) extracted by the responder from the ranging signal is:

[0031]

[0032]

[0033] The response signal y V (t) received by the verifier is:

[0034]

[0035] where heq_R (t) and h eq_A (t) are channel impulse responses of equivalent single-path channels between the responder and the verifier and between the attacker and the verifier, respectively;

[0036] The verifier generates the same amplitude gain parameter alpha and relative displacement parameter beta with the responder by using a random number seed seed, and the verifier calculates the local template signal STS in real time local (-t) and the cross-correlation function R V (t) of the current received signal, and determines the legal peak sequence from the cross-correlation function R V (t), and then takes the earliest time in the legal peak sequence as the arrival time of the response signal.

[0037] When there is an attacker in the system, N V +3 sharp peaks appear in R A +3 peaks, of which N A peaks come from the interference of the attacker, and only 3 peaks come from the response signal sent by the responder, and the verifier finds the legal peak sequence in the N A +3 peaks, wherein the ratio of the peak amplitude of the legal peak sequence to the corresponding amplitude gain parameter is the same, and the interval time between any two peaks is beta1, beta2.

[0038] The present application has the following beneficial effects:

[0039] The security ranging method based on dynamic response signal in the present application controls the generation of the response signal by using the encrypted payload data in the ranging signal when the verifier operates, the responder decrypts the encrypted payload data by using the initial key shared with the verifier, and generates the response signal according to the decrypted data, so that the local template of the verifier and the cross-correlation function of the received signal will appear the legal peak sequence with fixed amplitude gain and relative displacement generated by the response signal after receiving the response signal, and the verifier determines the arrival time of the response signal by detecting the legal peak sequence, and the attacker cannot recover the encrypted data in the payload data due to the lack of the key, so as to generate the attack signal with the same structure as the response signal, and therefore the attacker will not affect the ranging process, thereby ensuring the security of the ranging. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 It is a ranging system model diagram of UWB with an attacker;

[0041] Figure 2 It is a ranging process diagram under man-in-the-middle attack;

[0042] Figure 3 It is a ranging frame generation process diagram;

[0043] Figure 4 Fig. 2 is a ranging success rate curve diagram under different scenarios;

[0044] Figure 5 Fig. 3 is a detection success rate curve diagram under different scenarios;

[0045] Figure 6 Fig. 4 is a ranging error cumulative distribution function diagram under LOS scenario;

[0046] Figure 7 Fig. 5 is a ranging error cumulative distribution function diagram under NLOS scenario. DETAILED DESCRIPTION

[0047] In order to make the person skilled in the art better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments, and are not intended to limit the scope of the present application. In addition, in the following description, the description of the known structures and technologies is omitted to avoid unnecessary confusion of the concepts disclosed in the present application. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without making creative efforts should belong to the scope of protection of the present application.

[0048] The structural schematic diagrams according to the disclosed embodiments of the present application are shown in the drawings. These drawings are not drawn to scale, in which some details are exaggerated for the purpose of clear expression, and some details can be omitted. The shapes of various regions, layers and their relative sizes and positional relationships shown in the drawings are only exemplary, and in actuality, there can be deviations due to manufacturing tolerances or technical limitations, and the regions / layers with different shapes, sizes and relative positions can be additionally designed by the person skilled in the art according to actual needs.

[0049] Establishment of system model

[0050] There are three nodes in the system, namely a verifier, a responder and an adversary. The verifier needs to measure the distance from the responder to itself. The entire ranging process is divided into two stages. In the first stage, the verifier generates a ranging signal and sends it to the responder. In the second stage, after detecting the arrival of the ranging signal, the responder generates a response signal after a fixed delay processing time, and then sends it to the verifier. After detecting the arrival time of the response signal, the verifier calculates the distance between the verifier and the responder according to the round-trip delay time and the delay processing time of the responder.

[0051] The attacker detects whether a ranging process is currently happening by a limited number of preambles defined in the standard. When the frame structure of the communication of two legitimate ranging devices is known to the attacker, since both the signal transmission processes in the two phases are in the broadcast channel, it means that the ranging signal and the response signal sent by the verifier and the responder respectively can be obtained by the attacker. The attacker can send an attack signal in the first phase or the second phase to induce the receiver of the legitimate ranging device to make a false estimate of the first arrival time of the timing sequence, thereby affecting the ranging distance.

[0052] The UWB channel model proposed in IEEE 802.15.4a is based on the S-V model and is proposed after a large number of channel simulations and actual tests. The channel model is suitable for residential scenarios, office scenarios, factory scenarios and outdoor scenarios. In the S-V model, the multipath components arrive at the receiver in the form of clusters, and the channel impulse response h(t) is:

[0053]

[0054] where L is the number of clusters, K is the number of multipath components in each cluster, α l,k is the amplitude gain of the kth multipath component in the lth cluster, is the phase difference of the kth multipath component in the lth cluster, which is uniformly distributed in [0, 2π), T l is the propagation delay of the lth cluster, τ l,k is the relative propagation delay of the kth multipath component in the lth cluster.

[0055] Let the signal sent by the verifier in the first phase be x V (t), and the corresponding received signal of the responder be y R (t); the responder estimates the arrival time of the signal using the forward search algorithm after receiving y R (t), and then sends the signal x R (t) in the second phase, and the corresponding received signal of the verifier is y V (t). The received signals of the responder and the verifier are respectively:

[0056] y R (t) = x V (t) * h VR (t) + n(t)

[0057] y V (t) = x R (t) * h RV (t) + n(t)

[0058] where h VR(t) is a channel impulse response of a channel between the verifier and the responder, n(t) is white noise in the system, and since the channel is reciprocal, then h RV (t) = h VR (t).

[0059] The attacker can receive the signals sent by the verifier and the responder in two stages respectively, and suppose that the signals received by the attacker in the two stages are y A1 (t) and y A2 (t) are:

[0060] y A1 (t) = x V (t) * h VA (t) + n(t)

[0061] y A2 (t) = x R (t) * h RA (t) + n(t)

[0062] Wherein, h VA (t) and h RA (t) are channel impulse responses of communication channels between the attacker and the verifier and the responder respectively, the attacker attacks the ranging process in the first stage or the second stage, and the subsequent attack on the second stage will be called a man-in-the-middle attack.

[0063] The communication frame structure of the two legitimate ranging devices is known to the attacker, so after receiving the signal y A1 (t), the attacker will imitate the legitimate communication signal, send the attack signal x A (t) to the verifier, try to make the verifier think that the response signal arrives in advance, and realize the distance reduction attack, at this time the signal received by the verifier is:

[0064] y V (t) = x R (t) * h RV (t) + x A (t) * h AV (t) + n(t)

[0065] The security ranging method based on dynamic response signals provided by the application comprises the following steps:

[0066] 1) The verifier generates a ranging signal

[0067] The ranging frame of the verifier uses an STS sequence with a length of 128 bits as a timing sequence, and the load length is 256 bits, and the two legitimate ranging devices need to be initially paired before the ranging process starts, that is, the two parties share a pseudo-random number seed for generating the STS sequence and an initial key key1 for encrypting the load data.

[0068] The verifier generates a dynamic key key for encrypting the payload data in the next ranging frame before initiating each round of ranging process n and a random number seed seed, wherein the seed is used to generate parameters for controlling the structure of the response signal, the dynamic key key n and the length of the random number seed seed are both 128 bits, the verifier concatenates them into a plaintext sequence with a length of 256 bits, then uses the SHA-256 algorithm to map the key1 into an AES key with a length of 256 bits, and encrypts the plaintext sequence through the AES-256 algorithm to obtain the encrypted data D = (D1, D2,..., D 256 ) actually placed in the payload part for transmission.

[0069] Let the ranging signal generated after the ranging frame is modulated be s(t), which is:

[0070]

[0071] s(t) = P(t) + STS(t-T g ) + D(t-T g -T t )

[0072] Where D k is the kth bit of the payload sequence, p(t) is the pulse signal, T p is the duration of the pulse signal, T s is the symbol period of the payload sequence, P(t) is the synchronization signal, STS(t) is the modulated STS signal, T g is the duration of the synchronization signal, T t is the duration of the STS signal.

[0073] 2) Dynamic response signal generation;

[0074] The ranging signal y R (t) received by the responder from the verifier is:

[0075] y R (t) = s(t) * h VR (t) + n(t)

[0076] The responder calculates the cross-correlation function R local (t) of the local template signal STS R (t) and its received signal in real time, since the timing sequence of the verifier is composed of a segment of STS sequence, when the receiver receives y R (t), R R(t) a cluster of higher peaks will appear, and then the responder uses the two-way search algorithm to detect the first and last arrival time of the signal, denoted as tr_fir and tr_last, respectively.

[0077] Since the responder knows the structure of the ranging frame, after detecting the first arrival time of the ranging signal tr_fir, the responder determines that the payload part will appear in the time range of [tr_fir + T t , tr_fir + T t + T c ], where T c is the duration of D(t), and then the responder extracts the encrypted data in the payload to obtain the estimated value of the payload part

[0078] The responder has the same initial key key1 as the verifier, so the same AES key as the verifier is generated using the SHA-256 algorithm, and then the data is decrypted using the AES key, and the high 128 bits of the decrypted data is the dynamic key key n used in the next ranging process, and the low 128 bits is the random number seed seed.

[0079] The timing signal TM R (t) extracted by the responder from the ranging signal is:

[0080]

[0081] TM R (t) = y R (t) Rec(t)

[0082] = STS(t) * h VR (t + τ VR ) + n(t)

[0083] After time reversal and conjugation of TM R (t), the base signal g(t) is:

[0084]

[0085] The responder uses the random number seed seed extracted from the received payload data to generate two groups of random numbers α = (α1, α2) and β = (β1, β2) used to control the structure of the response signal, where α k ∈ [0.5, 2], β k ∈ [0, 1] and β1 < β2.

[0086] The response signal generated by the responder is composed of three basic signals with different amplitude gain parameters and relative displacement parameters, which are determined by a and β, respectively. The response signal x R (t) is:

[0087] x R (t) = g(t) + aig(t - β1T d ) + aig(t - β2T d )

[0088] where T d is the maximum relative displacement time, T d needs to be shared by both legitimate ranging devices before the ranging process starts, and T d is set to keep the response frame structure consistent in each round of ranging process, making it easier for the verifier to estimate the arrival time of the response signal.

[0089] 3) Secure ranging method of the verifier;

[0090] In the presence of an attacker in the system, the attacker can detect the arrival time of the ranging signal in the first stage and extract the timing signal part, denoted as TM A (t):

[0091] TM A (t) = STS(t) * h VA (t) + n(t)

[0092] The attacker will then try to generate an attack signal with the same structure as the legitimate response signal and send it to the verifier, causing the verifier to misjudge the arrival time of the response signal and achieve the distance reduction attack.

[0093] After detecting the first arrival time of the ranging signal, the attacker cannot obtain the random number seed seed from the encrypted payload data, which means that the attacker cannot accurately obtain the amplitude gain parameters and relative displacement parameters that determine the structure of the responder's timing signal.

[0094] Let g A (t) be the basic signal used to generate the attack signal. At this time, in order to improve the success rate of the attack, the attack signal is superimposed by several basic signals with different amplitude gain parameters and relative displacement parameters, both of which are randomly generated by the attacker. Denote the attack signal x A (t) as:

[0095]

[0096] where N A is the number of superimposed signals, and δ iis the ith amplitude gain parameter, λ i is the ith relative displacement parameter, T d is the maximum relative displacement time, where, δ i ∈ [0.5, 2], λ i ∈ [0, 1], both of which are random numbers generated by the attacker.

[0097] The response signal y V (t) received by the verifier is:

[0098]

[0099] where h eq_R (t) and h eq_A (t) are the channel impulse responses of the equivalent single-path channel between the responder and the verifier and between the attacker and the verifier, respectively, and their propagation time delays are τ VR and τ VA , respectively. When the attacker is located between the verifier and the responder, then τ VA ≤ τ VR From the perspective of the verifier, detecting the first arrival time of the responder's response signal x R (t) in a multipath channel is equivalent to detecting the occurrence time of the STS(-t) signal with fixed amplitude gain parameters and relative displacement parameters in an equivalent single-path channel.

[0100] Since the responder's response signal structure parameters are controlled by the random number seed seed generated by the verifier, the verifier can use the random number seed to generate the same amplitude gain parameters α and relative displacement parameters β as the responder. The verifier will calculate the cross-correlation function R local (t) of the local template signal STS V (-t) and the current received signal in real time. When there is an attacker in the system, there will be at most N A + 3 sharp peaks in R V (t), where N A peaks come from the attacker's interference, and only 3 peaks come from the responder's response signal. The verifier needs to find the legal peak sequence among the N A + 3 peaks. The ratio of the peak amplitudes of the legal peak sequence should be the same as the ratio of the corresponding amplitude gain parameters, and the pairwise interval times of the three peaks should be β1, β2, respectively. After finding the legal peak sequence, the earliest occurrence time of the three peaks is taken as the arrival time of the responder's signal. The specific detection method is shown in Table 1:

[0101] Table 1

[0102]

[0103]

[0104] Meanwhile, in the present application, in order to avoid the reuse of the key, the verifier will use different keys to encrypt the load data in each round of ranging process, and place the dynamic key used for the next round of encryption in the load data and send it to the responder. In the initial pairing stage, the legitimate ranging device realizes the sharing of the initial key, so that the responder will cache the dynamic key in the load data after receiving the ranging signal of the current round, and use the dynamic key to decrypt the load data in the next ranging signal. As can be seen, after the initial pairing, the responder can obtain the dynamic key used by the verifier in the subsequent ranging process, thereby realizing permanent pairing.

[0105] 4) Attack detection of the verifier.

[0106] In addition to being able to realize secure ranging, the present application can also detect whether there is an attacker in the current ranging process, which is discussed in two cases:

[0107] 41) After the highest peak Peak_1 in the first detection of R b (t) is found to have no matching legitimate peak sequence in the search center center1 and center2, the verifier considers that the highest peak Peak_1 is generated by the signal of the attacker, and determines that the current ranging process is attacked.

[0108] If the legitimate peak sequence is hit by the verifier once, that is, the highest peak Peak_1 found in the first search process is part of the legitimate peak sequence, and another two peaks that meet the conditions are found near the search center center1, center2, and the appearance times of the legitimate peak sequence are tr_1, tr_2 and tr_3 respectively, then when the verifier detects that there are peaks exceeding the noise threshold in the interval [tr_1, tr_2] and [tr_2, tr_3], it is determined that the current ranging process is attacked.

[0109] Figure 1The system model diagram of UWB ranging with an attacker, there are three nodes in the system, namely the verifier, the responder and the adversary, the verifier needs to measure the distance between the responder and itself, the whole ranging process is divided into two stages, the first stage is that the verifier generates ranging signals and sends them to the responder. The second stage is that the responder generates response signals after detecting the arrival of the ranging signals and after a fixed delay processing time, and sends them to the verifier. After detecting the arrival time of the response signals, the verifier calculates the distance between the two based on the round-trip delay time and the delay processing time of the responder.

[0110] Figure 2 The UWB ranging process diagram in the presence of an attacker. In the figure, T VA , T VR and T AR are the channel propagation delays between the verifier and the attacker, the verifier and the responder, and the attacker and the responder, respectively. The physical position of the attacker is between the verifier and the responder, so T VA <T VR and T AR <T VR . Assuming that the attacker and the responder have the same signal delay processing time T reply , the attack signal x adv (t) will arrive at the verifier before the response signal x res (t), and the difference between the arrival times of the two is: T AR + T VR -T VA .

[0111] Figure 3 The generation process diagram of the ranging frame, the verifier will generate a dynamic key key n for encrypting the load data in the next ranging frame and a random number seed seed before initiating each round of ranging process, wherein the seed is used to generate parameters for controlling the structure of the response signal, both of which have a length of 128 bits. The verifier splices them into a plaintext sequence with a length of 256 bits, then uses the SHA-256 algorithm to map key1 to an AES key with a length of 256 bits, and encrypts the plaintext sequence through the AES-256 algorithm to obtain encrypted data D=(D1, D2,..., D 256 ) actually placed in the load part for transmission.

[0112] Figure 4 The ranging success rate curve diagram of the secure ranging scheme based on dynamic response signals in different scenarios within a given signal-to-noise ratio range. From Figure 4As can be seen from the figure, the ranging success rate of the application in the outdoor NLOS scene is about 94%; for the other seven scenes, the ranging success rate of the application is more than 95%. Although under the influence of the attacker, the correlation function R V (t) will generate multiple peaks, but the verifier can find a set of legal peak sequences generated by the response signal among several peaks: the legal peak sequence has specific amplitude gain parameters and relative displacement parameters, and the two sets of parameters are controlled by the encrypted payload data transmitted by the verifier in the first stage, the responder can decrypt the encrypted payload data using the key shared with the verifier before the transmission process starts, and generate a response signal with the expected structure of the verifier according to the decrypted data, so as to facilitate the verifier to accurately estimate the arrival time of the response signal. The attacker cannot recover the encrypted data in the payload due to the lack of the key, so he cannot generate an attack signal with the same structure as the response signal, and therefore in this scheme, the attacker will not theoretically interfere with the ranging process, and the simulation results also confirm this phenomenon.

[0113] Figure 5 The figure is the false alarm rate curve of the application in a given signal-to-noise ratio range. As can be seen from the figure, in different scenes, the false alarm rate of the application is less than 99.5%.

[0114] Figure 6 And Figure 7 The figures are the cumulative distribution functions of the average ranging error of the application in four LOS scenes and four NLOS scenes. As can be seen from the figures, in the LOS scene, the probability of the ranging error being 0ns to 10ns is 97.2%; at the same time in the NLOS scene, the probability of the ranging error being 0ns to 10ns is 95.6%. And whether in the LOS scene or in the NLOS scene, the probability of the ranging error exceeding 20ns is not more than 1.5%.

Claims

1. A method of safety ranging based on dynamic response signals, characterized in that, The method comprises the following steps: The verifier generates a ranging signal and sends it to the responder; After detecting the arrival of the ranging signal, the responder generates a response signal after a fixed delay processing time, and then sends it to the verifier. The verifier controls the generation of the response signal by using the encrypted payload data in the ranging signal. The responder decrypts the encrypted payload data by using the initial key shared with the verifier, and generates the response signal according to the decrypted data; After detecting the arrival time of the response signal, the verifier calculates the distance between the verifier and the responder according to the round-trip delay processing time and the delay processing time of the responder. responder from a verifier is: wherein, is a ranging signal generated after the ranging frame is modulated, is a channel impulse response of the verifier-to-respondent communication channel, is white noise in the system; Response signal generated by responder Is: wherein, is the maximum relative displacement time, is the base signal, and are respectively the responder's use of a random number seed extracted from the received load data to generate two sets of random numbers for controlling the structure of the response signal, , and ; Base signal Is: wherein, a timing signal extracted from the ranging signal by the responder.

2. The dynamic response signal based safety ranging method of claim 1, wherein, Timing signals extracted by responders from ranging signals To: wherein, is the channel impulse response of the channel between the verifier and the responder at time t, is the duration of the STS signal, the first and last arrival times of the signal detected by the responder using the two-way search algorithm are denoted as and , is an intermediate variable.

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