Method for preventing privacy leakage in beam forming process based on router end space mapping mechanism

Abstract

The invention discloses a method for preventing privacy leakage in a beam forming process based on a router-end space mapping mechanism, which multiplexes the space mapping mechanism of a router, confuses signals used during channel detection at the router end, normally performs channel detection at a receiving end and sends a confused steering matrix back to the router end, so that the privacy leakage in the beam forming process is prevented. The hardware and the processing flow of the receiving end do not need to be modified, the mixing of the signals and the restoration of the steering matrix are completed at the router end, the zero change of the receiving end is realized, and the hardware change is greatly reduced. Compared with the prior art, the method has the advantages that the cost of wide application is remarkably reduced, communication is hardly influenced, and the method is suitable for actual scenes.

Description

Technical Field

[0001] The present invention relates to the problem of privacy leakage in the WiFi field, and in particular to the problem of privacy leakage in beamforming technology in the WiFi field. The present invention provides a method for preventing privacy leakage in the beamforming process based on a router-side space mapping mechanism. Background Art

[0002] In recent years, with the surge in the number and types of smart devices that support WiFi, they have been widely deployed. Beamforming technology is an important direction of WiFi technology, which can enhance WiFi signals and increase the signal-to-noise ratio. Beamforming technology is a technology that improves the signal transmission quality in wireless communication systems by weighting the transmitted signals. It can use antenna arrays or multiple individual antennas to focus and guide signals to obtain better signal quality at the target device or receiver. It has two main improvements over traditional WiFi: it enhances antenna signals, speeds up transmission speeds and increases signal range, and isolates conflict domains in space, increasing network throughput. Therefore, beamforming technology is currently widely used in various WiFi devices.

[0003] However, there is a privacy leakage problem in the beamforming process. The beamforming process is initiated by the router. After the receiving end performs channel measurement, it needs to calculate a steering matrix and send it back to the router. The router uses this steering matrix to guide the spatial mapping of the transmitting antenna. The steering matrix contains the spatial information around the receiving end. Although the steering matrix has lost some spatial information and only retains the information that guides the antenna steering, it will still leak the user's privacy information, such as location and activity, after processing. In addition, the steering matrix is ​​transmitted in plain text, and attackers can obtain the corresponding information from the data packet without decryption. Therefore, the beamforming process has the risk of user location privacy leakage.

[0004] At present, one solution is to encrypt the beamforming feedback packet CBF. This method can effectively prevent privacy leakage, but the computational overhead brought by encryption may cause additional burden on communication. In addition, this method requires updating the firmware on all WiFi devices to support encryption. Considering the huge number of existing WiFi devices, it is a very difficult task to widely apply this method. Another method is to inject fake beamforming feedback packets CBF to confuse the information collected by the attacker, but the router may not be able to distinguish the forged beamforming feedback packets CBF, resulting in the use of the wrong steering matrix for beamforming, which seriously reduces the communication performance. There is no better solution to the problem of privacy leakage in the beamforming process. Summary of the invention

[0005] In view of the defects of the prior art, the technical problem to be solved by the present invention is to overcome the problems of large computational overhead in solving the problem of privacy leakage in the beamforming process, which affects the communication performance, and large hardware changes lead to high costs for wide application. A method for preventing privacy leakage in the beamforming process based on the spatial mapping mechanism of the router is provided, that is, the spatial mapping mechanism of the router is reused, the signal used for channel detection is confused at the router end, the receiving end performs channel detection normally and sends the confused steering matrix back to the router end, the hardware and processing flow of the receiving end do not need to be modified, thereby ensuring minimal hardware changes, and the steering matrix is ​​restored at the router end to ensure that the beamforming can proceed normally.

[0006] The present invention is achieved by using the following technical solutions:

[0007] A method for preventing privacy leakage in a beamforming process based on a router-side spatial mapping mechanism comprises the following steps:

[0008] S1, the router generates a spatiotemporal confusion matrix Q based on the spatial mapping mechanism;

[0009] S2, using the spatiotemporal confusion matrix Q obtained in step S1 as the spatial mapping matrix for router beamforming channel detection;

[0010] S3, the router performs space mapping and sends a null data packet NDP to the receiving end;

[0011] S4, the receiving end calculates the confused steering matrix V based on the NDP received in step S3 obf ;

[0012] S5, the receiving end converts the steering matrix V obtained in step S4 obf After quantization and compression, it is sent back to the router in the form of a compressed beamforming feedback packet CBF;

[0013] S6: The router end decompresses the compressed beamforming feedback packet CBF received in step S5 and obtains the confused steering matrix V obf ;

[0014] S7, the router uses the spatiotemporal confusion matrix Q obtained in step S1 to transform the confused steering matrix V obtained in step S6 obf Perform restoration to obtain the restored steering matrix V;

[0015] S8. The router uses the restored steering matrix V to perform beamforming.

[0016] As a further improvement, in step S1 of the present invention, the router generates a spatiotemporal confusion matrix Q according to a spatial mapping mechanism, which is used to confuse the signal sent during channel detection, specifically:

[0017] Obtain the channel bandwidth and protocol type; refer to the corresponding relationship table of channel bandwidth, protocol type and channel subcarrier number, and determine the number of subcarriers k of the channel according to the channel bandwidth and protocol type; use QR decomposition technology to randomly generate a unitary matrix Q of size k×k, and the unitary matrix Q is used to confuse the signal used for subsequent channel detection.

[0018] As a further improvement, in step S2 of the present invention, the spatiotemporal confusion matrix Q obtained in step S1 is used as a spatial mapping matrix during router beamforming channel detection to confuse the signal sent during channel detection, specifically:

[0019] Replace the default direct mapping spatial mapping matrix that maps the transmit antenna on the router end to the spatial stream, and use the confusion matrix Q obtained in step S1 to perform spatial mapping on the transmit antenna. The signal sent during channel detection is the long training field LTF information X in the empty data packet NDP. LTF is a fixed signal in the protocol. The default direct mapping spatial mapping matrix will send LTF intact to the receiving end. After using the confusion matrix Q to perform spatial mapping on the transmit antenna, the signal transmitted by the router end to the receiving end is expressed as:

[0020] X obf =QX

[0021] Where X obf is the confused signal, Q is the confusion matrix, and X is the LTF information.

[0022] As a further improvement, in step S4 of the present invention, the receiving end calculates the obfuscated steering matrix V based on the NDP received in step S3. obf , the steering matrix V obf The time and space state information is obfuscated, specifically:

[0023] The unobfuscated NDP contains the long training domain LTF information X required for channel detection. The obfuscated NDP carries QX. After channel detection, the obfuscated steering matrix V is calculated. obf The process is as follows:

[0024] First, the receiver uses the obfuscated LTF signal QX to calculate the obfuscated channel state information CSI, which is expressed as:

[0025] H obf =HQ

[0026] Among them, H obfis the channel state information CSI after confusion, H is the channel state information without confusion, and Q is the confusion matrix. The steering matrix is ​​calculated from CSI using the SVD decomposition technique and is expressed as:

[0027]

[0028] Where U is the unitary matrix obtained after SVD decomposition, V obf is the steering matrix after confusion.

[0029] As a further improvement, in steps S4 and S5 of the present invention, the receiving end receives the empty data packet NDP and calculates the obfuscated steering matrix V obf The process of sending the received data to the router in the form of a compressed beamforming feedback packet CBF does not require any changes to the hardware and processing process of the receiving end. The hardware modification cost is extremely low. Specifically:

[0030] In the entire protection mechanism, the router uses the confusion matrix Q to confuse the channel detection signal, and the processing flow of the receiving end is not changed. The receiving end performs channel detection normally and calculates the steering matrix V obf It is sent to the router in the form of compressed beamforming feedback packet CBF. obf The restoration is performed at the router end, ensuring minimal modification at the receiving end and reducing costs.

[0031] As a further improvement, in step S7 of the present invention, the router uses the spatiotemporal confusion matrix Q obtained in step S1 to transform the confused steering matrix V obtained in step S6. obf The restored steering matrix V is obtained. The restored steering matrix V can perform normal beamforming without affecting normal communication. Specifically, it is:

[0032] The relationship between the obfuscated steering matrix and the unobfuscated steering matrix can be expressed as:

[0033]

[0034] Where V obf is the steering matrix after confusion, is the conjugate matrix of the confusion matrix, and V is the unconfused steering matrix. Since Q is a unitary matrix, we use V = QV obf The restored steering matrix V can be calculated, and the restored steering matrix V obtained by calculation can be used to perform spatial mapping on the transmitting antenna to achieve a normal beamforming process.

[0035] The beneficial effects of the present invention are as follows:

[0036] Beamforming technology is widely used in existing WiFi devices, but there is a privacy leakage problem in the beamforming process. The existing solutions have the problem of large computational overhead, affecting communication performance and large hardware changes, and the cost of widespread application is too high. In order to solve the problem that the existing solutions have large computational overhead and affect communication performance, the present invention uses the mathematical characteristics in the beamforming channel detection process. The router side generates the spatiotemporal confusion matrix Q according to the spatial mapping mechanism. When restoring from the confused steering matrix, it only needs to multiply the spatiotemporal confusion matrix Q, which has high computational efficiency and low overhead. The restored steering matrix can be used normally for beamforming, realizing efficient protection of personal location privacy without affecting communication performance; in order to solve the problem that the existing solutions have large hardware changes and the cost of widespread application is too high, the present invention reuses the spatial mapping mechanism of the router side, uses the spatiotemporal confusion matrix Q as the spatial mapping matrix during the router beamforming channel detection, and the confusion of the signal and the restoration of the steering matrix are completed on the router side, achieving zero changes on the receiving end, greatly reducing hardware changes. Compared with the prior art, the present invention significantly reduces the cost of widespread application, has almost no impact on communication, and is suitable for actual scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of the present invention;

[0038] Figure 2 It is a schematic diagram of an implementation of the present invention. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below by combining the accompanying drawings of the specification through specific embodiments:

[0040] The present invention aims at the problem of privacy leakage in the beamforming process, and aims to solve the problems that the existing solutions have large computational overhead, affect communication performance, require large hardware changes, and are too expensive for wide application. A method for preventing privacy leakage in the beamforming process based on a router-side spatial mapping mechanism is proposed. Figure 1 is a flow chart of the present invention;

[0041] The specific implementation method of the present invention is as follows:

[0042] S1. The router obtains the bandwidth and WiFi protocol of the current network channel, determines the number of subcarriers k of the channel according to the relationship between the bandwidth and the WiFi protocol and the number of subchannels, and uses the QR decomposition technology to randomly generate a unitary matrix of size k×k as the confusion matrix Q. The unitary matrix Q is used to confuse the signals used in subsequent channel detection. The confusion matrix is ​​regenerated in each beamforming process to prevent the confusion matrix from being cracked.

[0043] S2. Use the confusion matrix Q described in step S1 as the spatial mapping matrix for mapping the router transmit antenna to the spatial stream, replacing the default direct mapping spatial mapping matrix. The signal transmitted by channel detection during beamforming is the long training field LTF in the empty data packet NDP. It is a fixed signal in the protocol, denoted as X. The default direct mapping spatial mapping matrix will send the LTF intact to the receiving end. After using the confusion matrix Q for spatial mapping, the LTF transmitted by the router end is a confused signal, denoted as X. obf , the specific formula is:

[0044] X obf =QX

[0045] Where X obf is the signal obtained after confusion, Q is the confusion matrix, X is the long training domain LTF,;

[0046] S3, the receiving end receives the obfuscated LTF signal X described in step S2 obf After that, the default channel detection process is performed. After the receiving end performs channel detection, it will obtain the channel state feature CSI after confusion, which is recorded as H obf , and then the confused channel state feature H obf After SVD decomposition, the confused steering matrix V is obtained obf , expressed as:

[0047]

[0048] Where U is the unitary matrix obtained after SVD decomposition, V obf is the steering matrix after confusion, Σ is the singular value matrix denotes conjugation;

[0049] S4. According to the WiFi protocol, bandwidth, and MIMO configuration, the receiver selects the appropriate number of bits to convert the obfuscated steering matrix V obf Quantization compression is performed. There are two combinations of quantization bit numbers, namely 4 bits, 6 bits, and 7 bits, 9 bits. Two types of angle information are generated and written into the beamforming feedback packet CBF, and the beamforming feedback packet CBF is sent back to the router;

[0050] S5. After receiving the beamforming feedback packet, the router extracts the angle information from it and performs dequantization according to the quantization algorithm to obtain the confused steering matrix V obf ;

[0051] S6. The router uses the confusion matrix Q described in step S1 to restore the confused steering matrix. The relationship between the confused steering matrix and the unconfused steering matrix can be expressed as:

[0052]

[0053] Where V obf is the steering matrix after confusion, is the conjugate matrix of the confusion matrix, and V is the unconfused steering matrix. Since Q is a unitary matrix, we use V = QV obf The restored steering matrix V can be calculated;

[0054] S7. The router uses the restored steering matrix V as a spatial mapping mechanism for mapping transmit nature to spatial streams, and performs the subsequent process of normal beamforming.

[0055] The method of preventing privacy leakage in the beamforming process by using the router-side spatial mapping mechanism of the present invention is experimentally verified as follows:

[0056] In a laboratory setting, Figure 2 As shown, a router and two receivers are used to build an experimental scenario. The user moves around the router, including walking, stationary, and not in the room. The attacker sniffs the beamforming feedback packet outside the room and parses it, trying to analyze the user's spatial information. The user performs three states: walking, stationary, and not in the room, each state lasts for 3 minutes; the receiver connects to the router's WiFi and keeps the network high load by downloading large files; the attacker sniffs the beamforming feedback packet CBF during the beamforming process outside the room and groups the data in a window of 50 seconds; the router first takes no defense measures and performs beamforming normally, and then uses the present invention for defense, collecting 3 minutes of data for each of the three states, for a total of 9 minutes of data;

[0057] When the method for preventing privacy leakage in the beamforming process of the present invention is not used, the attacker can analyze the data in the beamforming feedback packet and determine that the user is in the room with an accuracy rate of up to 82.7% when the user is active in the room, and with an accuracy rate of up to 96.7% when the user is not in the room; when the method of the present invention is used, since the data in the beamforming feedback packet sniffed by the attacker has been obfuscated, the attacker can determine that the accuracy rate of both situations is about 50%, which is equivalent to random judgment; and the network speed is evaluated at the receiving end, and the defense method of the present invention has almost no effect on the network speed; while ensuring that privacy is not leaked in the beamforming process, the present invention reduces the computing overhead and reduces the impact on communication, and at the same time, the modification of the hardware is relatively small, which is suitable for application deployment in actual scenarios.

[0058] The above is not a limitation of the present invention. It should be pointed out that for ordinary technicians in this technical field, several changes, modifications, additions or substitutions can be made without departing from the essential scope of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preventing privacy leakage in a beamforming process based on a router-side spatial mapping mechanism, characterized in that: The following steps are involved: S1, the router generates a spatiotemporal confusion matrix Q based on the spatial mapping mechanism; S2, using the spatiotemporal confusion matrix Q obtained in step S1 as the spatial mapping matrix for router beamforming channel detection; S3, the router performs space mapping and sends a null data packet NDP to the receiving end; S4, the receiving end calculates the confused steering matrix V based on the NDP received in step S3 obf ; S5, the receiving end converts the steering matrix V obtained in step S4 obf After quantization and compression, it is sent back to the router in the form of a compressed beamforming feedback packet CBF; S6: The router end decompresses the compressed beamforming feedback packet CBF received in step S5 and obtains the confused steering matrix V obf ; S7, the router uses the spatiotemporal confusion matrix Q obtained in step S1 to transform the confused steering matrix V obtained in step S6 obf Perform restoration to obtain the restored steering matrix V; S8. The router uses the restored steering matrix V to perform beamforming.

2. The method for preventing privacy leakage in beamforming process based on router-side spatial mapping mechanism according to claim 1 is characterized in that: In the step S1, the router generates a spatiotemporal confusion matrix Q according to the spatial mapping mechanism, which is used to confuse the signal sent during channel detection, specifically: Obtain channel bandwidth and protocol type; determine the number k of subcarriers of the channel according to the channel bandwidth and protocol type; and randomly generate a unitary matrix of size k×k using QR decomposition.

3. The method for preventing privacy leakage in beamforming process based on router-side spatial mapping mechanism according to claim 1, characterized in that: In the step S2, the spatiotemporal confusion matrix Q obtained in step S1 is used as the spatial mapping matrix during the router beamforming channel detection to confuse the signal sent during the channel detection, specifically: The default direct mapping spatial mapping matrix for mapping the transmitting antennas at the router end to the spatial streams is replaced, and the confusion matrix Q obtained in step S1 is used to perform spatial mapping on the transmitting antennas.

4. The method for preventing privacy leakage in beamforming process based on router-side spatial mapping mechanism according to claim 1, characterized in that: In step S4, the receiving end calculates the obfuscated steering matrix V based on the NDP received in step S3. obf , specifically: The unobfuscated NDP contains the long training field LTF information X required for channel detection. The obfuscated NDP carries QX, and the obfuscated steering matrix V calculated after channel detection is obf The relationship with the unconfused steering matrix is: V = QV obf , the steering matrix V obf The time-space state information is obfuscated to hide the privacy information carried in V.

5. The method for preventing privacy leakage in beamforming process based on router-side spatial mapping mechanism according to claim 1, characterized in that: In step S5, the receiving end converts the steering matrix V obtained in step S4 into obf After quantization and compression, it is sent back to the router in the form of a compressed beamforming feedback packet CBF, specifically: In the entire protection mechanism, the router uses the confusion matrix Q to confuse the channel detection signal. The processing flow of the receiving end has not been changed. The receiving end performs channel detection normally and calculates the steering matrix V obf It is sent to the router in the form of compressed beamforming feedback packet CBF. obf The restoration is done on the router side.

6. The method for preventing privacy leakage in beamforming process based on router-side spatial mapping mechanism according to claim 1, characterized in that: In step S7, the router uses the spatiotemporal confusion matrix Q obtained in step S1 to transform the confused steering matrix V obtained in step S6. obf Restore and obtain the restored steering matrix V, which is: Using the spatiotemporal confusion matrix Q obtained in step S1, use V = QV obf The restored steering matrix V is calculated, and the calculated restored steering matrix V is used to perform spatial mapping on the transmitting antenna to achieve a normal beamforming process.

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