Mutual authentication and switching authentication method between radio frequency source and equipment in backscatter communication

Abstract

The invention discloses a mutual authentication and switching authentication method between a radio frequency source and equipment in backscatter communication. According to the method, the problems of mutual authentication between equipment and a radio frequency source in a backscatter communication system, switching authentication of long-distance mobile equipment and robustness in an authentication process are solved. The method effectively improves the safety of a backscatter communication system, is suitable for authentication of equipment and a radio frequency source in static and dynamic scenes, and particularly provides comprehensive safety guarantee for switching authentication requirements in a long-distance mobile scene. With the continuous development of the Internet of Things technology, the method provides powerful security support for various backscatter communication application scenes, and ensures that the communication process always keeps high security and reliability in various complex and dynamic environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of backscatter communication, and in particular relates to a mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication. Background Art

[0002] Backscatter Communication (BC) is an important technology that relies on passive devices for information transmission and is a key component in the passive Internet of Things (IoT). It achieves data collection and transmission without the need for external power or built-in batteries through energy harvesting and low-power design, showing great potential. Specifically, the backscatter device (BD) uses the received RF signal or other signals in the environment as a carrier, and by changing the impedance of the device antenna, the carrier signal is backscattered to the receiver with different amplitudes, phases or frequencies. The core advantage of this process is its ultra-low power consumption and low cost, making backscatter communication an ideal technology for realizing large-scale, distributed IoT devices.

[0003] Backscatter devices usually have a simple design structure, mainly composed of a backscatter modulation module, an information receiving module, an energy collection module, and possibly other functional modules (such as sensors). Because of its simple structure, the manufacturing cost of backscatter devices is low, but this also means that the energy and computing power of the device are limited. Such devices are usually unable to perform high-power or complex computing tasks, such as advanced cryptographic calculations. However, the low power consumption characteristics of backscatter devices enable them to be widely used in extreme environments or scenarios where regular maintenance is difficult, such as smart agriculture and wearable devices in the Internet of Things. By applying backscatter communication technology, devices in these scenarios can operate for a long time without frequent battery replacement, reducing maintenance costs and greatly improving system reliability.

[0004] Although backscatter communication systems have many advantages, their broadcast characteristics and the openness of wireless channels also bring about a variety of potential security threats. First, backscatter communication is vulnerable to passive attacks, such as eavesdropping and traffic analysis. Wireless passive eavesdropping attacks are one of the common types of threats in backscatter communication systems. Since the eavesdropper does not actively transmit signals when carrying out the attack, this attack method is extremely concealed and difficult to be detected by the system. By analyzing the traffic pattern in the reflected signal, the eavesdropper may obtain the identity information or confidential data of the device, thereby threatening the confidentiality of the system. This may not only lead to the leakage of the device's identity privacy, but also pave the way for more serious active attacks. In terms of active attacks, attackers can use stolen identity information to forge the device identity, illegally invade the system and implement a series of subsequent attacks, such as man-in-the-middle attacks, malicious data injection, core data theft, etc. These attacks seriously threaten the overall security of the backscatter communication system and may cause system failure or data loss. Therefore, ensuring the security of the backscatter communication system, especially protecting it from eavesdropping and identity forgery attacks, is a key prerequisite for reliable communication of the system.

[0005] In order to meet these security challenges, authentication technology has become an indispensable component of backscatter communication systems. The core task of authentication technology is to verify whether the device requesting access to the system has a legitimate identity, thereby establishing the first line of defense for the system. Physical layer security authentication technology is a method that uses the characteristics of the physical layer channel to identify or locate the signal source. Compared with traditional cryptography-based authentication technology, physical layer security authentication has unique advantages: it relies on the physical layer channel characteristics inherent in the device, which do not require additional calculations and are difficult to copy or forge. Therefore, physical layer security authentication can serve as a powerful supplement to cryptography-based identity authentication technology. By verifying whether the received signal comes from a legitimate device, it provides a strong guarantee for the secure communication of the backscatter communication system.

[0006] Currently, existing physical layer authentication schemes for backscatter communication systems can be divided into three categories according to the authentication objectives: authentication of devices, authentication of RF sources, and mutual authentication between RF sources and devices.

[0007] Device authentication is one of the most important research issues in backscatter communication systems. In backscatter communication, the Radio Frequency Source (RFS), also known as the Access Point (AP), is an active device that can perform complex cryptographic operations or extract physical layer channel characteristics to authenticate other devices. Some such schemes use different physical layer characteristics to implement physical layer security authentication that can resist identity forgery attacks, but these schemes do not support devices to authenticate the RF source.

[0008] Authentication of RF sources is complicated for backscatter devices because they cannot measure channels or perform cryptographic operations. Therefore, physical layer authentication schemes or cryptographic authentication schemes cannot be used to support backscatter devices to authenticate RF sources. Some such schemes can support backscatter devices to authenticate RF sources, but these schemes cannot support mutual authentication between RF sources and devices.

[0009] Existing solutions that support mutual authentication between devices and RF sources require backscatter devices to be able to measure signal strength, but this has certain limitations on application scenarios and cannot defend against eavesdropping and co-location attacks.

[0010] That is to say, although the existing technology has made some progress in the field of backscatter communication, it still has some significant shortcomings and limitations. Specifically, the current technology faces the following major problems:

[0011] 1) Lack of universal mutual authentication methods: Backscatter devices are difficult to support complex computing tasks due to their simple design and limited computing power. This makes it impossible to effectively authenticate the RF source through cryptographic methods in the existing technology. In addition, backscatter devices are unable to extract channel features, making it impossible to authenticate the RF source through physical layer authentication methods. This limitation leads to the lack of an effective mutual authentication mechanism between the device and the RF source in practical applications, increasing the risk of system attacks.

[0012] 2) Insufficient robustness: Existing technologies usually assume that the attacker attacks from a position half a wavelength away from the legitimate device to ensure that the attacker cannot obtain channel information that is highly correlated with the legitimate channel. However, this assumption ignores the threats of eavesdropping attacks and co-location attacks. Eavesdropping attackers can obtain sensitive information by passively monitoring the communication signals between the device and the RF source, thereby laying the foundation for subsequent active attacks (such as signal forgery, identity impersonation, etc.). Co-location attacks are more direct. When the attacker is close to the legitimate device, it is easier to obtain highly correlated channel information, thereby forging legitimate signals. These attacks may pose a serious threat to the system in actual application scenarios, but existing technologies have not yet fully considered and addressed these issues. Summary of the invention

[0013] In order to solve the above problems existing in the prior art, the present invention provides a mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication.

[0014] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0015] The present invention provides a mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication, comprising:

[0016] During the mutual authentication phase, the RF source uses the identity key s of the backscatter device k and session keys i , and the session information x to be sent i , by randomly adjusting the signal transmission power, generating the current round of RF source signal and sending it to the backscattering device; the identity key s k is generated by the server when the backscatter device registers with the server, and the identity key s k The session key s is sent by the server to the RF source. When the backscatter device is a device that has not been mutually authenticated with any RF source, the RF source is the RF source closest to the backscatter device determined by the server. i The radio frequency source is based on the identity key s k Random generation;

[0017] The backscattering device calculates the received current round of RF source signal y i (l+1) and the reference signal y of the RF source r The normalized cosine similarity between the two is calculated, and the legitimacy of the radio frequency source is verified based on the normalized result obtained, and if it is legal, the identity key s is used to verify the legitimacy of the radio frequency source. k and the information to be sent x b Generate the encrypted current round scattering signal x bs (l+1) is sent to the RF source; the reference signal y of the RF source r It is obtained by the backscatter device through interaction with the radio frequency source before the mutual authentication stage;

[0018] The RF source receives the channel impulse response h of the last round of scattered signals. i,k (l) 2 , the channel impulse response h to the received current round of scattered signal i,k (l+1) 2 Verification is performed by using the reflection coefficient α of the backscattering device and the randomly adjusted signal transmission power used to generate the current round of RF source signals, verifying the signal power of the received current round of scattering signals, determining the legitimacy of the backscattering device based on the verification result, and completing mutual authentication; wherein the random numbers used to generate different rounds of RF source signals are different; the reflection coefficient α, and the channel impulse response of the received previous round of scattering signals when the current round of scattering signals is the first round of scattering signals in the authentication phase, are all obtained through interaction with the backscattering device before the mutual authentication phase.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1) Low computing requirements and high versatility: The authentication scheme of the present invention fully considers the limited computing power of backscatter devices, and designs a simple and effective computing method so that the backscatter device can authenticate the RF source. This design reduces the requirements for device computing power, ensures that the scheme can run smoothly on low-power and resource-constrained devices, and improves the versatility of the scheme. In contrast, existing schemes that support mutual authentication between devices and RF sources require more complex computing resources, limiting their application in low-energy devices. The low-threshold computing design of the authentication scheme of the present invention makes the authentication scheme of the present invention more suitable for promotion and application in large-scale, multi-scenario IoT deployments.

[0021] 2) High-accuracy authentication mechanism: The authentication scheme of the present invention uses the channel impulse response (CIR) and the received signal strength (RSS) as the fingerprint of the physical layer to authenticate the legitimacy of the device. The channel impulse response and the received signal strength are inherent characteristics of the physical layer and are difficult to forge or tamper with, so they can provide a reliable means of identity authentication for the backscattering device. In addition, in order to further defend against replay attacks, the present invention also adopts a strategy of randomly adjusting the power of the excitation signal, so that even if the attacker can capture the legitimate signal, it is difficult to bypass the authentication by a simple replay method, thereby achieving accurate authentication of the backscattering device. In addition, the present invention also uses the method of detecting the signal composition pattern to authenticate the radio frequency source. This process can not only confirm the legitimacy of the radio frequency source, but also protect the content of the transmission signal by encryption to prevent eavesdroppers from stealing sensitive information, significantly enhancing the system's ability to resist eavesdropping attacks, active attacks and co-location attacks, ensuring the security of the signal transmission process, reducing the risk of being attacked, making the authentication process more reliable, and significantly improving the accuracy of authentication. Compared with the existing schemes that support mutual authentication between devices and radio frequency sources, which may have the risk of misjudgment and missed judgment, the authentication scheme of the present invention can more effectively identify legitimate devices and radio frequency sources, reduce the error rate in the authentication process, and thus improve the overall security and stability of the system.

[0022] 3) Highly robust security protection: The authentication scheme of the present invention can not only resist a variety of active attacks such as identity forgery, replay, relay attacks, signal forgery, etc., but also effectively defend against eavesdropping and co-location attacks through key encryption. This all-round security protection design enables the system to maintain a high degree of robustness in the face of various complex attacks, ensuring the security and integrity of communications. Compared with existing solutions that support mutual authentication between devices and radio frequency sources, which have deficiencies in defending against eavesdropping and co-location attacks, the authentication scheme of the present invention further enhances the system's anti-attack capabilities through multi-level protection measures, ensuring the reliable operation of the system.

[0023] In summary, the authentication scheme of the present invention has shown obvious advantages in reducing the computing burden of devices, improving authentication accuracy, and enhancing security protection capabilities. It not only adapts to the needs of device diversity and scenario complexity in current backscatter communication systems, but also provides a more secure and reliable solution for future large-scale Internet of Things deployments.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is an architecture diagram of a backscatter communication system provided by an embodiment of the present invention;

[0026] Figure 2 It is a flow chart of a mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication provided by an embodiment of the present invention;

[0027] Figure 3 It is a process diagram of the registration phase, the authentication phase and the switching authentication phase in the mutual authentication and switching authentication method between the radio frequency source and the device in the backscatter communication provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0029] The present invention provides a mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication. The method is applied to a backscatter communication system. The system includes three entities such as Figure 1 As shown in the figure, they are: server, RF source and backscatter device. The server is static and honest and trustworthy. It is the controller of the system and controls the RF source to transmit signals to stimulate the backscatter device to communicate. Multiple RF sources are evenly distributed in the system. The coverage areas of adjacent RF sources are connected but not overlapped, so that the movable backscatter communication device can receive signals from different RF sources in the system to support device communication. The RF source in the coverage area to which the device belongs is defined as the source RF source, and the RF source in the coverage area that the device enters after long-distance movement is defined as the destination RF source. The RF sources are semi-trustworthy. They will follow the protocol and send signals to specific backscatter devices according to the instructions of the server to obtain feedback. The backscatter devices are distributed in the coverage area of ​​the RF source and communicate with the RF source in a backscattering manner.

[0030] Assuming that the communication between the server and each RF source is secure, they can authenticate each other and encrypt the communication through complex cryptographic techniques, making it impossible for attackers to decode the communication information. The RF source and the backscatter device in the system communicate in time division duplex (TDD) mode, and the communication round can be expressed as L = [1, 2, ..., l, ...]. In each round of communication, the uplink channel and the downlink channel meet reciprocity, and in the relevant rounds, the channels show high correlation.

[0031] Assume that the adversary has strong capabilities and can launch the following attacks:

[0032] 1) Eavesdropping attack: The attacker passively monitors the channel between the backscatter device and the RF source to perform an eavesdropping attack. The attacker eavesdrops and intercepts the original signal between the backscatter device and the RF source to analyze the channel status, traffic, and other information.

[0033] 2) Active attack: The attacker has a certain distance from the backscatter device or RF source (greater than the half wavelength of the signal between the backscatter device and the RF source), and actively injects the signal into the channel between the backscatter device and the RF source, attempting to pass the authentication by signal injection. The attacker can try to deceive the backscatter device or RF source by identity forgery, replay, relay, and signal forgery. The attacker launches an identity forgery attack by modifying the identity. The attacker transmits false messages and deceives the receiver, thereby disguising himself as a legitimate backscatter device or RF source. The attacker can also use eavesdropping attacks to intercept the signal between the backscatter device and the RF source, and launch a replay attack by retransmitting the signal in the previous communication round, or directly forward the signal of the current round to the receiver to launch a relay attack. In addition, the attacker can analyze the signals in multiple rounds of communication and forge signals to launch signal forgery attacks.

[0034] 3) Co-location attack: The attacker approaches the legitimate backscatter device as close as possible and attacks it, aiming to deceive the RF source. Since the attacker is too close to the RF source and can be easily discovered by the RF source, we only consider the scenario where the co-location attacker is close to the backscatter device. In this case, the attacker can use highly correlated channels to launch identity forgery, replay, relay, and signal forgery attacks on the RF source.

[0035] In order to solve the technical problems in the background technology, the present invention designs a method for mutual authentication and switching authentication between a radio frequency source and a device in backscatter communication, which method may include three stages:

[0036] 1) Registration phase: The device registers on the server side. After the server starts the location prediction model based on the device's location information, it helps the device negotiate keys with the RF source in the device's coverage area. The device and the RF source use the negotiated key to initialize authentication during the registration phase.

[0037] 2) Authentication stage: The RF source and the device communicate normally, and the received signal is used to determine whether the signal source is a legitimate device.

[0038] 3) Switching authentication phase: After a long-distance mobile device moves from a source RF source to a destination RF source, the destination RF source determines whether the device is a legitimate device through a server and generates a new key. The device confirms the signal source through the received signal to complete the switching authentication.

[0039] The following will describe in detail the method for mutual authentication and switching authentication between a radio frequency source and a device in backscatter communication provided by the present invention.

[0040] Figure 2 FIG. 1 is a flow chart of a mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication provided by an embodiment of the present invention, such as Figure 2 As shown, the method includes:

[0041] S101, in the mutual authentication phase, the RF source uses the identity key s of the backscattering device k and session keys i , and the session information x to be sent i , by randomly adjusting the signal transmission power, the current round of RF source signal is generated and sent to the backscattering device; the identity key s k The identity key s is generated by the server when the backscatter device registers with the server. k It is sent by the server to the RF source during the registration phase of the backscatter device. When the backscatter device is a device that has not performed mutual authentication with any RF source, the RF source is the RF source closest to the backscatter device as determined by the server; the session key s i During the registration phase, the RF source uses the identity key s k Randomly generated.

[0042] S102, the backscattering device calculates the received current round of radio frequency source signal y i (l+1) and the reference signal y of the RF source r The normalized cosine similarity between them is used to verify the legitimacy of the RF source based on the normalized result, and if it is legitimate, the session key s is used to verify the legitimacy of the RF source. i and the information to be sent x b Generate the encrypted current round scattering signal x bs (l+1) is sent to the RF source; the reference signal y of the RF sourcer It is obtained during the registration phase through communication interaction between the backscatter device and the RF source.

[0043] S103, the RF source receives the channel impulse response h of the last round of scattered signals. i,k (l) 2 , the channel impulse response h to the received current round of scattered signal i,k (l+1) 2 Verification is performed by using the reflection coefficient α of the backscattering device and the randomly adjusted signal transmission power used to generate the current round of RF source signals to verify the signal power of the received current round of scattering signals, and the legitimacy of the backscattering device is determined based on the verification result to complete mutual authentication; wherein, the random numbers used to generate different rounds of RF source signals are different; the reflection coefficient α, and the channel impulse response of the previous round of scattering signals received when the current round of scattering signals is the first round of scattering signals in the authentication phase, are all obtained during the registration phase through communication interaction between the RF source and the backscattering device.

[0044] Here, the above steps S101 to S103 belong to the backscattering device BD k AP with RF source i The mutual authentication phase between Figure 3 As shown, before the mutual authentication phase, the backscatter device BD k Steps to register with the server, and when the backscatter device BD k If the device has not previously performed mutual authentication with any RF source, the backscatter device BD before the mutual authentication phase k AP with RF source i The interactive steps include the following steps:

[0045] S01, Backscatter Device BD k By reflecting the environmental signal, it sends its own identity information to the server. k signal.

[0046] S02, the server uses the backscatter device BD k The signal sent to the backscatter device BD k Perform positioning and determine the distance from the backscatter device BD based on the positioning results k The nearest RF source AP i , and according to the second random number r k and backscatter device BD k The identity information sent k Generate identity keys k and secretly returns it to the backscatter device BD k , the identity information B k and identity keysk Sent secretly to the RF source AP i .

[0047] Specifically, the backscatter device BD k The identity information can be transmitted by reflecting the baseband signal transmitted by the server. k Send it to the server. After receiving the identity information b k Then, first, for the backscatter device BD k Generate identity keys k =f(b k ,r k ), where function f() represents a hash function, r k ∈(0,1]; Then, the backscattering device BD is detected based on the received signal strength RSS and the arrival angle AoA k For positioning, assume that the server's position is L = (x0, y0), and the backscatter device BD k The position of L0 is L0 = (x k ,y k ), then x k =x0+dsinAoA,y k =y0+dcosAoA, where the server and the backscatter device BD k The distance between P is the power of the received signal. After the server locates the device, it starts the existing path prediction model and calculates the path prediction value based on the backscatter device BD. k Position L0 helps backscatter device BD k Determine the closest RF source AP i , the server will backscatter device BD k Identity informationb k and keys k Sent secretly to the device BD through beamforming technology k , secretly sent to the RF source AP through cryptography technology i , to prevent eavesdroppers from obtaining key information in this step.

[0048] S03, RF source AP i According to the identity key s k Randomly generate session keys i , and according to the identity key s k and session keys i , by randomly adjusting the signal transmission power, generating the initial RF source signal and sending it to the backscattering device BD k .

[0049] Specifically, the radio source AP i Received equipment BDk Identity informationb k and identity keys k After that, first use the random number r i Generate and Device BD k Session key in, represents XOR operation; secondly, the radio source AP i Using identity keys k and session keys i Generated signal (i.e. the initial RF source signal, also called the baseband signal) Send to device BD k , where P i RF source AP i The maximum signal transmission power (i.e., maximum transmission power), ρ t and ρ i For two different power parameters and satisfy

[0050] S04, Backscatter Device BD k The received initial RF source signal is used as the RF source AP i The reference signal y r And save it for subsequent use in the RF source AP i The authentication is performed and the reflection coefficient α is used to reflect the received initial RF source signal to the RF source AP. i ; Among them, the backscatter device BD k Reflected to the RF source AP i The initial RF source signal is used as the initial scattered signal.

[0051] Specifically, equipment BD k The signal received at (i.e. the initial RF source signal received) y i,k =h i,k x i,k +ω k , where h i,k Indicates device BD k AP with RF source i CIR between k Indicates device BD k Noise at the equipment BD k This signal y i,k As a RF source AP i The reference signal y r And save it for the RF source AP in subsequent sessions i After that, the device BD k The signal y i,k Reflected to the RF source AP i .

[0052] S05, RF source AP i Extract the reflection coefficient α and the RF source AP from the received initial scattered signal i With backscatter device BD k The channel impulse response between the two is saved for subsequent backscattering device BD k certification.

[0053] Specifically, the radio source AP i The signal received at (i.e. the initial scattered signal received) Where α is the device BD k The reflection coefficient, I k =αh k,i ω k BD for device k Due to the interference caused by the reflected signal, ω i It is a radio source AP i The noise at . According to the channel reciprocity, h i,k =h k,i , RF source AP i From the signal y k,i Extract channel features from And use this feature as device BD k Fingerprint of the device, which is used for device BD in subsequent sessions k certification.

[0054] In some embodiments, the above S101 is implemented by the following steps:

[0055] S1011, RF source AP i Use the first random number r to adjust its maximum transmission power P i , get the adjusted maximum transmission power

[0056] S1012: According to the session information x to be sent i , session key i , the first power parameter ρ t and the adjusted maximum transmission power Generate the first signal portion

[0057] S1013, according to the identity key s k , the second power parameter ρ i and the adjusted maximum transmission power Generate the second signal portion

[0058] S1014: According to the first signal part With the second signal part Generate the current round of RF source signal and send it to the backscatter device BD k .

[0059] For example, the mutual authentication phase between the RF source and the backscatter device can continue to refer to the above Figure 3 Authentication phase in. Exemplarily, the expression of the current round of RF source signal is as follows:

[0060]

[0061] Among them, x i (l+1) represents the current round of RF source signal, l+1 represents the current round, l represents the previous round, and r∈(0,1] is the RF source AP i A randomly selected random number, P i Indicates the radio source AP i The maximum transmission power.

[0062] In some embodiments, in the above S102, the backscatter device BD k The received current round RF source signal y i (l+1) can be expressed as: Among them, h i,k (l+1) is the backscatter device BP k AP with RF source i The CIR of the current round between k Backscatter Device BD k The noise at the RF source AP i The current round RF source signal y i (l+1) and RF source AP i The reference signal y r The cosine similarity between i It can be expressed as:

[0063]

[0064] In this formula, y i Represents the above y i (l+1),y r ·y i Represents y r With y i The convolution of |y i | means y i The norm of |y r |Similarly. Since the RF source AP i Possess the identity key s negotiated during the registration phase k and session keys i , so if the received signal y iFrom the RF source AP i ,y i With the reference signal y r The cosine similarity normalization result between |e i | Close to 1, if the received signal comes from an unknown identity key s k and session keys i The normalized cosine similarity result is close to 0. Therefore, device BD k The cosine similarity normalization result can be used to determine the RF source AP using an appropriate threshold. i Whether it is legal.

[0065] In some embodiments, the “verifying the legitimacy of the radio frequency source based on the obtained normalization result” in the above S102 can be implemented by the following steps:

[0066] S1021, when the normalized result e i Greater than or equal to the preset normalization threshold δ i When the radio source is AP i Legal. For example, the normalization threshold δ is preset i Greater than or equal to 0.5 and less than or equal to 1.

[0067] S1022, when the normalized result e i Less than the preset normalization threshold δ i When the radio source is AP i Illegal.

[0068] In some embodiments, in the above S102, "according to the identity key s when legal" k and the information to be sent x b Generate the encrypted current round scattering signal x bs (l+1) is sent to the radio frequency source" can be implemented as follows: using the identity key to send the information x b The encryption code is: And use the backscattering method to bs (l+1) is sent to the RF source AP i .

[0069] In some embodiments, in the above S103, “the RF source receives the channel impulse response h of the last round of scattered signals received” i,k (l) 2 , the channel impulse response h to the received current round of scattered signal i,k (l+1) 2Verification is performed by using the reflection coefficient α of the backscattering device and the randomly adjusted signal transmission power used to generate the current round of RF source signals to verify the signal power of the received current round of scattered signals, and determining the legitimacy of the backscattering device based on the verification results. This can be achieved by the following steps:

[0070] S1031, RF source AP i Calculate the channel impulse response h of the last round of scattered signal received i,k (l) 2 The channel impulse response h of the received current round of scattered signal i,k (l+1) 2 The distance d(l) between them.

[0071] Since the same channel has high correlation during the correlation time, the CIR during the correlation time can be expressed using a first-order Gauss-Markov process as:

[0072]

[0073] Where a is the channel correlation coefficient, which can be measured using the Yule-Walker equation and the Crame-Rao lower bound, and η is the noise. i Measured from the same device BD k The CIR satisfies the following formula:

[0074]

[0075] in, Indicates that due to device BD k The reflected signal generates self-interference. Therefore, the RF source AP between adjacent communication rounds i The distance d(l) between the measured CIRs can be expressed as: Therefore, the RF source AP i The available threshold δ k The relationship between the distance d(l) and the backscatter device BD k the legitimacy of.

[0076] S1032, RF source AP i According to the backscatter device BD k The reflection coefficient α, and the randomly adjusted signal transmission power used to generate the current round of RF source signal Calculate the signal power and convert the calculated signal power into Compare with the signal power of the received current round of scattered signal.

[0077] In the current round of communication, due to the radio source AP i By size The signal power of the transmitted signal is thus transmitted in the backscattering device BD k Under legal circumstances, the RF source AP i The size of the received backscattered signal should also be Therefore, the backscatter device BD can be determined by whether the calculated signal power is the same as the received signal power. k the legitimacy of.

[0078] S1033: When the calculated distance d(l) is less than or equal to the preset distance threshold δ k , and when the calculated signal power is the same as the signal power of the received current round of scattered signals, it indicates that the backscattering device BD k legitimate.

[0079] S1034: When the calculated distance d(l) is greater than the preset distance threshold δ k , and / or, when the calculated signal power is different from the signal power of the received previous round of scattered signals, it indicates that the backscattering device BD k Illegal.

[0080] Through the above two verification steps, the RF source AP i The channel characteristics can be verified by BD for device k Perform authentication. i Determine the backscatter device BD k After legalization, it can be used with backscatter equipment BD k Send and receive data to be sent.

[0081] It should be noted that during the registration phase and when communicating with the backscatter device BD k During the authentication phase, in each round of communication, the RF source AP i The random numbers used each time are randomly generated.

[0082] In actual applications, the backscatter device may move from the coverage of one RF source (source RF source) to the coverage of another RF source (destination RF source) during long-distance movement. In this case, since the destination RF source does not store any information about the device before receiving the switching authentication signal from the backscatter device, it is unable to immediately determine whether the device is a legitimate device when the switching authentication signal arrives. As for the backscatter device, due to its limited capabilities, it is also difficult to distinguish whether the received signal comes from different RF sources. Therefore, current technology is difficult to cope with the switching authentication problem in this scenario. To address this problem, the present invention also designs a specific authentication mechanism, so that the backscatter device can smoothly complete the authentication switching between different RF sources when moving long distances, thereby ensuring the continuity and security of communication. Specifically, in combination with the above Figure 3 The handover authentication phase in the embodiment further includes the following steps after S101 and before S102:

[0083] S201, backscatter device BD k Calculate the received current round RF source signal y i (l+1) and the reference signal y of the RF source r The cosine similarity between (l+1) , and the received RF source signal y i (l) and the reference signal y of the RF source r The cosine similarity between (l) When the absolute value of the similarity difference between them is less than the preset difference threshold δ, it indicates that the backscattering device BD k Currently still in the RF source AP i coverage range, no need to switch authentication; when the similarity difference is greater than or equal to the preset difference threshold δ, it indicates that the backscatter device BD k Moved to the target radio source AP j coverage, you need to switch authentication.

[0084] S202: When switching authentication, the backscatter device BD k Your identity information k Sent to the target radio source AP j .

[0085] S203, target radio source AP j The identity information k Send to server.

[0086] When moving equipment over long distances k When the cosine similarity between the received signal and the reference signal decreases, the degree of decrease in the adjacent round exceeds the threshold device BD kIt can be realized that this result may be that it has moved to the destination radio source AP j Therefore, the device BD k Start the handover authentication phase. Device BD k The identity information k Using environmental signals j Backscatter to the destination RF source AP j , RF source AP j Receive identity information b k After that, the identity information b k Send to the server.

[0087] S204: The server sends a signal to the target radio source AP. j Authentication is performed and the identity key s is sent after the authentication is passed k Secretly sent to the target RF source AP j .

[0088] The server can authenticate the RF source AP through a cryptographic algorithm j And confirm the RF source AP through path prediction j Device BD in the overlay domain k After authentication, the server will send the identity key s k Secretly sent to the target RF source AP j .

[0089] S205, backscatter device BD k The target radio source AP j Communicate with each other to make the target RF source AP j Backscatter Device BD k Generate new session keys j And obtain the reflection coefficient α, target RF source AP j With backscatter device BD k The channel impulse response between the backscatter device BD k Store the target radio source AP j The reference signal y′ r .

[0090] Specifically, the RF source AP j Using a randomly selected random number r j Generate a new session key Then, the RF source AP j Using identity keys k and session keys j Generate signal And send to the device BD k . Equipment BD kThe RF source AP can be identified by recalculating the absolute value of the cosine similarity difference and comparing the recalculated absolute value with a preset difference threshold. j After the authentication is passed, the reference signal y of the RF source stored in itself is sent to r Update to the target radio source AP j The reference signal y′ r And backscatter the signal. RF source AP j Received equipment BD k The reflected signal is then extracted and saved by the device BD k Channel characteristics Used for subsequent mutual authentication. Specifically, device BD k Get the target radio source AP j The reference signal y′ r , and RF source AP j Get device BD k Channel characteristics The principle is the same as that of S03 to S05 above, and will not be repeated here.

[0091] S206, target radio source AP j With backscatter device BD k Based on the data obtained in the mutual communication, the mutual authentication phase is entered to complete the mutual authentication.

[0092] Specifically, the target radio source AP j and backscatter device BD k The specific principle of the mutual authentication phase is to i and backscatter device BD k The principle of the mutual authentication phase is the same as that of the authentication phase and will not be repeated here.

[0093] Obviously, the switching authentication scheme provided by the present invention can meet the needs of seamless switching of long-distance mobile devices between different RF sources. In the process of moving the device from the source RF source to the target RF source, the server plays a key role. By supporting key negotiation and key update, the device can quickly complete the authentication and continue to communicate securely after entering the coverage range of the new RF source. This scheme not only ensures the communication security between the device and the target RF source during the switching process, but also ensures that the subsequent communication process can continue to use the updated key for encrypted transmission, further improving the security of the overall system.

[0094] In summary, the present invention mainly solves the following key technical problems:

[0095] First, the present invention solves the mutual authentication problem between the backscatter device and the radio frequency source. In the backscatter communication system, the radio frequency source usually has strong computing power and can authenticate other devices through an upper layer authentication scheme based on cryptography or a physical layer authentication scheme based on a physical channel. However, due to its simple design, the backscatter device cannot support complex cryptographic operations and cannot even measure channel parameters, which makes mutual authentication between the device and the radio frequency source extremely difficult. The prior art has failed to effectively solve this problem, and the present invention utilizes the unique characteristics of the physical layer signal to enable the backscatter device to effectively authenticate with the radio frequency source, thereby improving the overall security of the system.

[0096] Secondly, the present invention also solves the problem of switching authentication between different RF sources for a backscatter device that moves over long distances. In practical applications, a backscatter device may move from the coverage of one RF source (source RF source) to the coverage of another RF source (destination RF source) during long-distance movement. In this case, since the destination RF source does not store any information about the device before receiving the switching authentication signal from the backscatter device, it is unable to immediately determine whether the device is a legitimate device when the switching authentication signal arrives. As for the backscatter device, due to its limited capabilities, it is also difficult to distinguish whether the received signal comes from different RF sources. Therefore, current technology is difficult to cope with the switching authentication problem in this scenario. The present invention designs a specific authentication mechanism so that the device can smoothly complete the authentication switching between different RF sources when moving over long distances, thereby ensuring the continuity and security of communication.

[0097] In addition, the present invention also pays special attention to the robustness of the authentication process. The current physical layer authentication scheme based on physical layer features usually assumes that the distance between the adversary and the legitimate device is greater than half the wavelength of the signal to avoid the channel observed by the adversary being highly correlated with the channel between the legitimate device, thereby preventing the adversary from forging physical layer features that can pass authentication. However, in practical applications, the adversary can flexibly choose the attack method, especially when the distance between the adversary and the device is close, the success rate of the attack will be significantly improved. Therefore, defending against co-location attacks has become one of the problems to be solved urgently. In order to deal with such attacks, the present invention designs a highly robust authentication scheme, which can still ensure the reliability of authentication even when the distance between the adversary is close, thereby effectively defending against co-location attacks. At the same time, the present invention also considers the defense problem of eavesdropping attackers. Eavesdropping attacks are usually not fully considered in existing authentication schemes, because eavesdropping attacks are hidden and difficult to detect, and are often used as preliminary preparations for attackers to implement more serious active attacks (such as identity forgery, replay, relay and signal forgery attacks, etc.). The attacker eavesdrops on the signal characteristics between the analysis device and the radio frequency source, and forges the signal based on this to launch an attack. Therefore, in order to ensure the high robustness of the authentication scheme, the present invention pays special attention to the defense against eavesdropping attacks during the design process, so that the system can effectively respond to eavesdropping attacks, further improving the overall security.

[0098] In summary, the present invention solves the problems of mutual authentication between devices and radio frequency sources in backscatter communication systems, switching authentication of long-distance mobile devices, and robustness of the authentication process. This solution effectively improves the security of the backscatter communication system. With the increasing application of the Internet of Things, it is crucial to ensure the security and reliability of communication equipment in various complex environments. The proposal of the present invention not only fills the gap in the prior art in terms of technology, but also provides a solid foundation for the further development of backscatter communication technology. In the future, with the further development of the Internet of Things technology, the application scenarios of backscatter communication systems will become more diversified and complex. Therefore, it is necessary to continue to explore and improve the physical layer-based security authentication mechanism to cope with the increasing security challenges and ensure the security and reliability of the backscatter communication system in different application scenarios.

[0099] The present invention also provides a medical information system, comprising: an implantable medical device as a backscattering device, a hospital management end as a server, and different department medical devices as different radio frequency sources, wherein the backscattering device and the radio frequency source use the above-mentioned method for mutual authentication; wherein, before each mutual authentication, the hospital management end is used to use the department medical device currently required to be used as the department medical device currently required to be mutually authenticated with the implantable medical device according to the patient's treatment plan, and the implantable medical device is used to measure the patient's clinical data or to control the release of drugs, and after mutual authentication with the corresponding department medical device, the measured clinical data is sent to the department medical device or the release of drugs is controlled according to the control instructions of the department medical device, and accordingly, the medical device is used to treat the patient or assist the doctor in treating the patient; when the implantable medical device needs to be registered and mutually authenticated with the next department medical device, the hospital management end is also used to verify the implantable medical device, and after the verification is passed, the identity key of the implantable medical device is secretly sent to the next department medical device, so that the next department medical device and the implantable medical device can be mutually authenticated.

[0100] Specifically, embedded medical devices can act as sensors to measure clinical data such as blood pressure and heart rate of patients, and feed back to the hospital's medical equipment to help doctors make clinical medical decisions; they can also act as drug controllers to control the time and concentration of drug release under the control of external medical devices to help patients recover. Since medical devices are closely related to patients' privacy data and are related to the treatment effect and even life safety of patients, protecting the communication security between implantable medical devices and external medical devices is of great significance to protecting patients' life safety.

[0101] In the field of implantable medical devices, the solution proposed by the present invention involves the registration stage, the authentication stage and the switching authentication stage, which can provide all-round security protection for the implantable medical device system. Among them, the registration stage can protect against unregistered implantable medical devices from entering the system; the authentication stage supports mutual authentication between implantable medical devices and external devices to prevent the privacy information in the implantable medical devices from being stolen, and at the same time prevents the external devices from receiving false information; the implantable medical device moves with the human body. If the patient needs joint treatment in different departments, the switching authentication stage can support the implantable medical device to switch authentication between external devices in different departments, ensuring secure communication between the implantable medical device and external devices in different departments.

[0102] Exemplarily, the operation process of this implementation case includes three parts:

[0103] 1) Registration phase: The implantable medical device is registered at the hospital management end, and the hospital management end generates an identity key for the implantable medical device. Since the departments that need to participate in the treatment of the patient can be determined by the treatment plan, the hospital management end does not need to perform path prediction analysis on the implantable medical device. After the identity key is generated, the medical device in the department where the patient first receives treatment is used as the source RF source of the implantable medical device. The hospital management end transmits the identity key to the medical device as the source RF source using a password encrypted method. The medical device generates a session key based on the identity key, and uses the identity key and session key to generate a reference signal and send it to the registered implantable medical device, and records the physical layer characteristics of the device's reflected signal to complete the registration.

[0104] 2) Authentication stage: The implantable medical device formally communicates with the medical device that serves as the source RF source to obtain patient health information or perform treatment. In each round of communication, the implantable medical device and the medical device verify the received signal and authenticate the sender of the signal.

[0105] 3) Switching authentication phase: When the patient completes treatment in the current department and goes to the next department for treatment, the hospital management end verifies the patient through the patient's identity information and registration information, thereby verifying the implanted medical device. After that, the hospital management end sends the identity key of the implanted medical device to the medical device in the department waiting for treatment using a password encryption method. The medical device acts as the destination RF source and performs switching authentication with the implanted medical device. The medical device, which acts as the destination RF source, generates a new session key based on the identity key, and uses the identity key and the new session key to generate a reference signal and send it to the registered implanted medical device, and records the physical layer characteristics of the device's reflected signal to complete the switching authentication. After switching authentication, the implanted medical device and the medical device, which acts as the destination RF source, can formally communicate.

[0106] The present invention also provides an intelligent drug management system, comprising: a drug tag as a backscattering device, a pharmaceutical factory management device as a server for producing drugs with drug tags, and devices of different operators or users who need to purchase or count drugs as different radio frequency sources; the backscattering device and the radio frequency source are registered and mutually authenticated using the above method; the process of mutual authentication between the drug tag and a device is the process of counting drugs or the process of buying and selling management; when a pharmaceutical factory, operator or user currently holds drugs, and a purchaser or counter needs to purchase or count drugs from the pharmaceutical factory, operator or user who currently holds drugs, the pharmaceutical factory, operator or user who currently holds drugs secretly sends the identity key of the drug tag of the drug to the device of the purchaser or counter through its own device, so that the device of the purchaser or counter and the drug tag carried by the drug are mutually authenticated to realize the purchase management or counting of drugs.

[0107] Backscatter communication equipment can be attached to drugs as tags to help pharmaceutical factories, distributors, hospitals and pharmacies to conduct intelligent drug management, trace the entire process of drug production and circulation, prevent the circulation of counterfeit drugs, and protect the rights and interests of pharmaceutical factories, hospitals, pharmacies and customers who buy drugs. It can also prevent malicious third parties from obtaining information on drug labels and counterfeiting labels.

[0108] The application of the solution proposed in the present invention in the field of intelligent drug management equipment involves the registration stage, the authentication stage and the switching authentication stage, which can provide all-round security protection for the intelligent drug management system. Among them, the registration stage can protect against unregistered drugs from entering the system; the authentication stage supports mutual authentication and identification between drugs and management equipment; drugs will be displaced during the circulation process, and the switching authentication stage can switch and authenticate drugs between scanning devices in pharmaceutical factories, hospitals and pharmacies to ensure the traceability of the drug circulation process. In the event of a dispute, this method can also be used as proof to confirm the authenticity of the drug.

[0109] Exemplarily, the operation process of this implementation case includes three parts:

[0110] 1) Registration stage: After the drug is manufactured, a backscatter tag is attached, and the pharmaceutical factory management device generates an identity key for it. Since the circulation of drugs can be determined by the purchase records of hospitals or pharmacies, the pharmaceutical factory management device does not need to perform path prediction analysis on the tag. After the identity key is generated, the management end of the drug purchaser (distributor, etc.) serves as the source RF source of the tag. The pharmaceutical factory can send the identity key to the management end as the source RF source through other confidential methods. After the management end generates the session key, it uses the identity key and session key to generate a reference signal, sends it to the tag, and records the characteristics of the tag to complete the registration.

[0111] 2) Authentication stage: The tag device and the management end device as the source RF source formally communicate for management such as drug inventory or buying and selling. In each round of communication, the tag device and the management end as the source RF source verify the received signal and authenticate the sender of the signal.

[0112] 3) Switching authentication stage: When the drug transaction is completed, the distributor can hand over the device's identity key and the corresponding drug to the buyer through the purchase record. After that, the buyer's management end uses the tag device's identity key to generate a new session key, and uses the identity key and the new session key to generate a reference signal and send it to the tag device, recording the physical layer characteristics of the device's reflected signal to complete the switching authentication. After switching authentication, the tag device and the buyer's management end can communicate formally for drug inventory or sale, etc.

[0113] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0114] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0115] In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality of components. Certain measures are recorded in different embodiments, but this does not mean that these measures cannot be combined to produce good effects.

[0116] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for mutual authentication and switching authentication between a radio frequency source and a device in backscatter communication, characterized in that: include: During the mutual authentication phase, the RF source uses the identity key s of the backscatter device k and session keys i , and the session information x to be sent i , by randomly adjusting the signal transmission power, generating the current round of RF source signal and sending it to the backscattering device; the identity key s k is generated by the server when the backscatter device registers with the server, and the identity key s k The session key s is sent by the server to the RF source. When the backscatter device is a device that has not been mutually authenticated with any RF source, the RF source is the RF source closest to the backscatter device determined by the server. i The radio frequency source is based on the identity key s k Random generation; The backscattering device calculates the received current round of RF source signal y i (l+1) and the reference signal y of the RF source r The normalized cosine similarity between the two is calculated, and the legitimacy of the radio frequency source is verified based on the normalized result obtained, and if it is legal, the identity key s is used to verify the legitimacy of the radio frequency source. k and the information to be sent x b Generate the encrypted current round scattering signal x bs (l+1) is sent to the RF source; the reference signal y of the RF source r It is obtained by the backscatter device through interaction with the radio frequency source before the mutual authentication stage; The RF source receives the channel impulse response h of the last round of scattered signals. i,k (l) 2 , the channel impulse response h to the received current round of scattered signal i,k (l+1) 2 Verify the signal power of the received current round of scattered signals by using the reflection coefficient α of the backscattering device and the randomly adjusted signal transmission power used to generate the current round of RF source signals, determine the legitimacy of the backscattering device according to the verification result, and complete mutual authentication; wherein the random numbers used to generate different rounds of RF source signals are different; The reflection coefficient α, and the channel impulse response of the received previous round of scattered signals when the current round of scattered signals is the first round of scattered signals in the authentication phase, are both obtained through interaction with the backscattering device before the mutual authentication phase.

2. The mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication according to claim 1, characterized in that: The RF source uses the backscatter device's identity key s k and session keys i , and the session information x to be sent i , by randomly adjusting the signal transmission power, generating the current round of RF source signal and sending it to the backscattering device, including: The radio frequency source uses the first random number to adjust its own maximum transmission power to obtain an adjusted maximum transmission power; According to the session information x to be sent i , the session key s i , the first power parameter ρ t and the adjusted maximum transmission power, generating a first signal part; According to the identity key s k , the second power parameter ρ i and the adjusted maximum transmission power, generating a second signal portion; The current round of RF source signal is generated according to the first signal part and the second signal part and sent to the backscattering device.

3. The mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication according to claim 2, characterized in that: The expression of the current round RF source signal is as follows: Among them, x i (l+1) represents the current round RF source signal, l+1 represents the current round, l represents the previous round, r represents the first random number, P i Indicates the maximum transmission power of the RF source.

4. The mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication according to claim 1, characterized in that: The verifying the legitimacy of the radio frequency source based on the obtained normalization result includes: When the normalization result is greater than or equal to a preset normalization threshold, it indicates that the RF source is legal; the preset normalization threshold is greater than or equal to 0.5 and less than or equal to 1; When the normalization result is less than the preset normalization threshold, it indicates that the radio frequency source is illegal.

5. The mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication according to claim 1, characterized in that: The RF source receives the channel impulse response h of the last round of scattered signals. i,k (l) 2 , the channel impulse response h to the received current round of scattered signal i,k (l+1) 2 Verifying the signal power of the received current round of scattered signals by using the reflection coefficient α of the backscattering device and the randomly adjusted signal transmission power used to generate the current round of radio frequency source signals, including: The RF source calculates the channel impulse response h of the last round of scattered signals received i,k (l) 2 The channel impulse response h of the received current round of scattered signal i,k (l+1) 2 The distance between them is d(l); The RF source calculates the signal power according to the reflection coefficient α of the backscattering device and the randomly adjusted signal transmission power used to generate the current round of RF source signals, and compares the calculated signal power with the signal power of the received current round of scattered signals.

6. The mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication according to claim 5, characterized in that: Determining the legitimacy of the backscatter device according to the verification result includes: When the calculated distance d(l) is less than or equal to the preset distance threshold, and the calculated signal power is the same as the signal power of the received current round of scattered signals, it indicates that the backscattering device is legal; When the calculated distance d(l) is greater than a preset distance threshold, and / or the calculated signal power is different from the signal power of the received current round of scattered signals, it indicates that the backscattering device is illegal.

7. The mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication according to claim 1, characterized in that: The step of registering the backscatter device with the server, and when the backscatter device is a device that has not yet mutually authenticated with any radio frequency source, the step of interacting with the radio frequency source before the mutual authentication phase comprises the following steps: The backscatter device sends its own identity information b to the server by reflecting the environmental signal. k signal; The server locates the backscatter device according to the signal sent by the backscatter device, determines the radio frequency source closest to the backscatter device according to the positioning result, and locates the backscatter device according to the second random number and the identity information b k Generate the identity key s k and secretly returns it to the backscattering device, and the identity information b k and the identity key s k secretly sent to the radio frequency source; The radio frequency source is based on the identity key s k The session key s is randomly generated i , and according to the identity key s k and the session key s i , generating an initial radio frequency source signal by randomly adjusting the signal transmission power and sending it to the backscattering device; The backscatter device receives the initial RF source signal as the reference signal y of the RF source r and save it for subsequent authentication of the radio frequency source, and use the reflection coefficient α to reflect the received initial radio frequency source signal to the radio frequency source; wherein the initial radio frequency source signal reflected by the backscattering device to the radio frequency source is used as the initial scattering signal; The radio frequency source extracts the reflection coefficient α and the channel impulse response between the radio frequency source and the backscattering device from the received initial scattered signal and saves them for subsequent authentication of the backscattering device.

8. The mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication according to claim 1, characterized in that: The backscattering device calculates the received current round RF source signal y i (l+1) and the reference signal y of the RF source r Before calculating the normalized cosine similarity between the two, the method further comprises: The backscattering device calculates the received current round of RF source signal y i (l+1) and the reference signal y of the RF source r The cosine similarity between the received RF source signal y i (l) and the reference signal y of the RF source r When the absolute value is less than a preset difference threshold, it indicates that the backscatter device is still in the coverage of the radio frequency source and does not need to switch authentication; when the absolute value is greater than or equal to the preset difference threshold, it indicates that the backscatter device has moved to the coverage of the target radio frequency source and needs to switch authentication; When switching authentication, the backscatter device sends its own identity information b k Sending to the target radio frequency source; The target radio frequency source transmits the identity information b k Sending to the server; The server authenticates the target radio frequency source and sends the identity key s k secretly sending it to the target radio frequency source; The backscatter device communicates with the target radio frequency source so that the target radio frequency source generates a new session key for the backscatter device and obtains the reflection coefficient α, the channel impulse response between the target radio frequency source and the backscatter device, and so that the backscatter device stores a reference signal of the target radio frequency source; The target radio frequency source and the backscatter device enter the mutual authentication phase according to the data obtained in the mutual communication to complete the mutual authentication.

9. The mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication according to claim 1, characterized in that: The backscatter device is an implantable medical device, the server is a hospital management end, and different radio frequency sources are medical devices of different departments; wherein, before each mutual authentication, the hospital management end is used to use the department medical device currently needed as the department medical device that currently needs to be mutually authenticated with the implantable medical device according to the patient's treatment plan, and the implantable medical device is used to measure the patient's clinical data or to control the release of drugs and after mutual authentication with the corresponding department medical device, the measured clinical data is sent to the department medical device or the release of drugs is controlled according to the control instructions of the department medical device. Accordingly, the medical device is used to treat the patient or assist the doctor in treating the patient; when the implantable medical device needs to be mutually authenticated with the next department medical device, the hospital management end is also used to verify the implantable medical device, and after the verification is passed, the identity key of the implantable medical device is secretly sent to the next department medical device, so that the next department medical device and the implantable medical device can be mutually authenticated.

10. The mutual authentication and switching authentication method between a radio frequency source and a device in backscatter communication according to claim 1, characterized in that: The backscatter device is a drug tag, the server is a pharmaceutical factory management device for producing drugs with the drug tags, and different radio frequency sources are devices of different operators or users who need to purchase or count the drugs; wherein, the process of mutual authentication between the drug tag and a device is the process of counting the drugs or the process of buying and selling management; and, when a pharmaceutical factory, operator or user currently holds the drug, and a purchaser or counter needs to purchase or count the drugs from the pharmaceutical factory, operator or user currently holding the drug, the pharmaceutical factory, operator or user currently holding the drug secretly sends the identity key of the drug tag of the drug to the device of the purchaser or counter through its own device, so that the device of the purchaser or counter and the drug tag carried by the drug are mutually authenticated to achieve purchase management or inventory of the drug.

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