Delayed Doppler-Based Key Generation Method for Secure Wireless Communications

Abstract

Computer-implemented delay-Doppler-domain-based key generation method for secure wireless communication between at least two devices

Description

[Technical Field]

[0001] The present invention relates to a computer-implemented key generation method for secure wireless communication between at least two devices. [Background technology]

[0002] Securing wireless links is becoming increasingly challenging with the deployment of heterogeneous networks. Due to the differences in capabilities of network entities, it is not possible to apply traditional cryptographic methods at all nodes.

[0003] Traditional cryptographic mechanisms used in wireless systems require significant computational power for communicating nodes. Furthermore, the encryption / decryption process introduces additional latency. Physical layer security (PLS) offers an alternative approach using the characteristics of the wireless channel. This includes key generation-based techniques in which a secret sequence is extracted from the shared propagation medium. Key generation techniques rely on the interrelationship of channel characteristics, such as channel impulse response (CIR), channel frequency response (CFR), and received signal strength (RSS), which generally limits their applicability to time-division duplex (TDD) systems. On the other hand, frequency-division duplex (FDD) systems do not experience reciprocal channels, which makes it difficult to generate a shared key in such systems.

[0004] Frequency division duplex (FDD) systems have a clear advantage in terms of latency compared to time division duplex (TDD) systems, but it comes at the cost of increased complexity in terms of channel estimation. Specifically, TDD systems exploit the channel reciprocity in the uplink (UL) and downlink (DL), thus reducing channel estimation overhead. However, this is only effective for channels with long coherence times (such that both UL and DL transmissions occur within this duration).

[0005] However, FDD systems do not experience reciprocal channel response. Therefore, to generate a shared key, FDD systems rely either on the combined UL and DL channels (which require the same coherence time as TDD systems) or on parameters that are similarly observed at both communicating nodes. Examples of the latter include using delays and angles between nodes to generate equivalent keys. Delays, while reciprocal, require large bandwidths to provide sufficient resolution, and using angles requires the presence of multiple antennas at the communicating nodes.

[0006] A few studies have been proposed for PLS in FDD systems using wireless channel characteristics. Most of these studies involve estimation of the combined (uplink and downlink) channel using some kind of feedback between communicating nodes, such as pilot loopback [1], combined CFR [2], and precoding matrix indicator (PMI) feedback [3].

[0007] An alternative is to use frequency-invariant channel parameters such as delay [4] or angle [5]. The former takes into account device-to-device (D2D) scenarios where time-varying distances (or propagation delays) are used for key generation.

[0008] The angle of arrival (AoA) method in both the elevation and azimuth dimensions is used to generate the key [6]. The angle-based method [6] is extended to unmanned aerial vehicle (UAV) multiple-input multiple-output (MIMO) systems, and the 3D spatial angle between legitimate nodes is used to generate the key. The eigenvalue correlation of the channel covariance matrix [7] is also used to construct a reciprocal channel [8], which is then used to generate the key.

[0009] Among the aforementioned works, the combined channel-based method suffers from the drawback of extra latency caused by the feedback process, while the angle-based method requires a large number of antennas at the communication nodes. Moreover, the covariance matrix-based technique gives a low key generation rate (KGR) [9].

[0010] This invention exploits the capabilities of orthogonal time-frequency space (OTFS) and the underlying symplectic Fourier transform to convert a fast-fading wireless channel (in the time-frequency domain) into a slowly varying wireless channel (in the delay-Doppler domain). Recently, the confidentiality performance of OTFS-based transmissions has been investigated for uplink satellite

[10] and unicast services

[11] . The former considers eavesdropping satellites and cooperative UAV jammers, while the latter analyzes the impact of eavesdropper mobility on confidentiality. A channel-based pre-rotation has been proposed

[12] , which leads to constellation distortion at the eavesdropper. A channel-dependent seed is employed in

[13] to generate a Gosudarstvennyi standard base sequence and then use it to perturb the OTFS modulation to secure the transmission.

[0011] As a result, all of the above-mentioned problems have created a need to provide novelty in the relevant field. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] S.J. Goldberg, Y.C. Shah, and A. Reznik, "Method and apparatus for performing JRNSO in FDD, TDD and MIMO communications," March 19, 2013, U.S. Patent No. 8,401,196. [Non-patent literature]

[0013] [Non-Patent Document 1] X. Wu et al., "A secret key generation method based on CSI in OFDM FDD system," Globecom Workshops (GC Wkshps). IEEE, 2013, pp. 1297-1302. [Non-patent document 2] H. Taha and E. Alsusa, "Secret key exchange using private random precoding in MIMO FDD and TDD systems," IEEE Trans. Veh. Technol., vol. 66, no. 6, pp. 4823-4833, 2016. [Non-patent document 3] O. Gungor, F. Chen, and C. E. Koksal, "Secret key generation from mobility," in Globecom Workshops (GC Wkshps). IEEE, 2011, pp. 874-878. [Non-patent document 4] Badawy et al., "Secret key generation based on AoA estimation for low SNR conditions," 81st Veh.Technol.Conf.(VTC Spring).IEEE, 2015, pp. 1–7. [Non-Patent Document 5] K. Lin et al., "Secret key generation based on 3D spatial angles for UAV communications," Wireless Commun.Netw.Conf.(WCNC).IEEE, 2021, pp. 1–6. [Non-patent document 6] B. Liu, A. Hu, and G. Li, "Secret key generation scheme based on the channel covariance matrix eigenvalues ​​in FDD systems," IEEE Commun. Lett., vol. 23, no. 9, pp. 1493-1496, 2019. [Non-Patent Document 7] G. Li et al., "Constructing reciprocal channel coefficients for secret key generation in FDD systems," IEEE Commun. Lett., vol. 22, no. 12, pp. 2487–2490, 2018. [Non-patent document 8] J. Zhang et al., "A new frontier for IoT security emerging from three decades of key generation relying on wireless channels," IEEE Access, vol. 8, pp. 138-406–138-446, 2020. [Non-Patent Document 9] J. Hu et al., "Secrecy analysis for orthogonal time frequency space scheme based uplink LEO satellite communication," IEEE Wireless Commun. Lett., vol. 10, no. 8, pp. 1623-1627, 2021. [Non-Patent Document 10] Z. Tie et al., "Security performance analysis for an OTFS-based joint unicast-multicast streaming system," IEEE Trans. Commun., vol. 70, no. 10, pp. 6764–6777, 2022. [Non-Patent Document 11] J. Sun, Z. Wang, and Q. Huang, "Secure precoded orthogonal time frequency space modulation," 13th Int. Conf. Wireless Commun. Signal Process. (WCSP). IEEE, 2021, pp. 1-5. [Non-Patent Document 12] W. Liang et al., "Underlying security transmission design for orthogonal time frequency space (OTFS) modulation," Sensors, vol. 22, no. 20, pp. 7919, 2022. Summary of the Invention [Problem to be solved by the invention]

[0014] The main objective of this invention is to establish a secure key generation method for secure wireless communication between at least two devices in FDD and TDD systems, and to mitigate different security threats such as eavesdropping, jamming, and spoofing, especially in high mobility scenarios.

[0015] Another object of the present invention is to provide a security key generation method that does not require multiple antennas at the device / communication node in FDD and TDD systems. [Means for solving the problem]

[0016] The present invention discloses a secure key generation method in which security keys are generated based on delay-Doppler domains, more specifically, the keys are generated based on delay and Doppler bin indices and quantized fractional delay and Doppler values.

[0017] The figures and related descriptions necessary for a better understanding of the subject matter of the present invention are given below. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of devices communicating with each other. [Figure 2] 3 is a flow chart illustrating the start-up steps of the present invention. [Figure 2a] 1 is a flow chart illustrating the steps of the present invention in a TDD system. [Figure 2b] 3 is a flow chart showing the steps of the present invention in an FDD system. [Figure 2c] 1 is a flow chart showing the final steps of the present invention. [Figure 3] 1 is a schematic diagram of a system configured to perform the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] For a better understanding of the subject matter of the present invention, reference will be made to the parts and components given in the drawings.

[0020] The present invention relates to a computer-implemented key generation method for secure wireless communication between at least two devices and a communication method using said security key, a system for performing said key generation method or said communication method, and a program comprising instructions for causing a computer, e.g., said system, to perform said method.

[0021] The devices are configured to communicate with each other. The devices of the present invention are any devices capable of wireless communication. They may be communication nodes, base stations, mobile devices (e.g., smartphones, laptops, etc.), or fixed devices.

[0022] In Figure 1, two devices are shown as device A (10a) and device B (10b). Device A (10a) is shown as a base station, and device B (10b) is shown as a device located on a moving vehicle moving in the direction of the arrow. The vehicle shown with a dotted line represents the previous location of the vehicle. Also shown in Figure 1 is an unauthorized user (I), which is a person or system that poses security threats such as eavesdropping, jamming, and spoofing.

[0023] Referring to Figure 2, first, a delay-Doppler grid is designed and the location of pilot symbols within the grid is determined. The location of the pilot symbols on the grid is known by both Device A (10a) and Device B (10b).

[0024] In a preferred embodiment, the dimensions of the delay Doppler grid in both directions are calculated according to at least one, and preferably all, of the available bandwidth, the number of available subcarriers, the subcarrier spacing, and the transmission duration.

[0025] In the first stage of the method, the pilot signal is in the delay Doppler domain. The signal is converted to the time domain for transmission between device A (10a) and device B (10b). In one embodiment, the conversion is performed using an inverse symplectic Fourier transform (ISFT) followed by a Heisenberg transform.

[0026] The time domain pilot signal is converted back to the delay and Doppler domain at device A (10a) and device B (10b), and delay and Doppler values ​​are obtained from the signal at both device A (10a) and device B (10b). Preferably, a channel estimation framework method or framework is used to obtain the delay and Doppler values. Preferably, the conversion is performed by using a Wigner transform followed by a symplectic Fourier transform (SFT).

[0027] Referring to Figure 2c, the delay and Doppler bin indices for the shared wireless channel (WC) are then obtained, either by calculation or by checking the system, and fractional delay and Doppler values ​​are obtained, where the indices are the first part of the shared secret. These fractional delay and Doppler values ​​are then quantized, and the quantized values ​​are the second part of the shared secret. These values ​​are used to generate a shared security key.

[0028] To generate the shared security key, the delay and Doppler bin indices and the quantized fractional delay and Doppler values ​​are converted to binary representations. For integer delay and Doppler indices, the decimal representation (base 10) is converted directly to binary (base 2). For the fractional portions of the delay and Doppler shifts, the values ​​are first converted and divided by the quantization interval, and the result is converted to binary equivalents as the integer portions. It is also possible to directly divide the full (integer and fractional) delay and Doppler values ​​by the quantization interval and convert them to binary representations.

[0029] A method for generating security keys for secure wireless communication between at least two devices, the method comprising the steps of: designing a delay-Doppler grid and determining locations of pilot symbols; converting delay-Doppler pilot signals to the time domain on both devices; transmitting time-domain pilot signals to each other by the devices and converting the pilot signals to the delay-Doppler domain by the devices; obtaining delay-Doppler values ​​at both devices; obtaining indices of the delay-Doppler values ​​at both devices; and obtaining and quantizing fractional delay-Doppler values ​​at both devices.

[0030] As can be seen in Figure 2, at this point there is a decision phase to determine whether the system is a frequency division duplex (FDD) or a time division duplex (TDD) system. However, this decision step is optional. The method can be configured to work with only frequency division duplex or only time division duplex systems. For both frequency division duplex (FDD) or time division duplex (TDD) systems, the method follows the same steps, although the order of the steps may differ.

[0031] Referring to Figure 2a, if the system is determined to be a frequency division duplex system (FDD), both devices (Device A (10a) and Device B (10b)) transmit converted pilot signals to each other simultaneously. Then, each of Device A (10a) and Device B (10b) converts the signal to the delay-Doppler domain and obtains delay and Doppler values ​​from the signal.

[0032] Referring to Figure 2b, if the system is determined to be a time division duplex system (TDD), device A (10a) transmits a converted pilot signal to device B (10b), which converts the received signal to the delay-Doppler domain and obtains delay and Doppler values ​​from the signal. Device B (10b) then transmits the time-domain converted pilot signal to device A (10a), which converts the signal to the delay-Doppler domain and obtains delay and Doppler values ​​from the signal.

[0033] 2a and 2b, for both Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems, pilot signals are transmitted between devices and the received signals are converted to the delay-Doppler domain to obtain delay and Doppler values ​​from the signals. The only difference here is the order of transmission. In Time Division Duplex systems, transmissions are simultaneous between devices, while in Frequency Division Duplex systems, the same transmissions are sequential.

[0034] For both time division duplex (TDD) and frequency division duplex (FDD) systems, the remaining steps are the same key generation steps described above.

[0035] In a preferred embodiment, the above steps are followed by information reconciliation, which is used to eliminate key mismatches. In the present invention, it is primarily used to address Doppler shifts for both nodes, especially in FDD scenarios where Doppler is not reciprocal but is related to the specific carrier frequency of the uplink / downlink transmissions.

[0036] In a preferred embodiment, the above steps are followed by privacy amplification, which is used to increase the randomness of the generated keys.

[0037] The method is executed by a computer or a system as described below. The program comprises instructions for executing the method on the computer or the system as described below. The program may be stored on a computer-readable medium.

[0038] Referring to Figure 3, a system is configured to perform the same above-described method, comprising at least two devices (Device A (10a) and Device B (10b)), both of which are equipped with at least one antenna (A) for communicating with each other over a wireless channel (WC).

[0039] Both devices comprise at least one processing unit (PU) for performing the same above-mentioned method steps.

[0040] In a preferred embodiment, the processing units (PUs) are configured to perform specific steps of the method of the present invention. For example, device A (10a) includes a processing unit (PU) configured to design a delay-Doppler grid and pilot allocation and convert the delay-Doppler to a time-domain signal. Device B (10b) includes a processing unit (PU) configured to convert the time domain to the delay-Doppler domain, estimate delay and Doppler values ​​and indices, and quantize the estimated delay / Doppler values. Alternatively, one specific processing unit (PU) can be used separately for each function.

[0041] In an alternative embodiment, both devices comprise a processing unit (PU) configured to perform all steps and functions. Preferably, the processing units (PU) of both devices are identical.

[0042] References 1. S.J. Goldberg, Y.C. Shah, and A. Reznik, “Method and apparatus for performing JRNSO in FDD, TDD and MIMO communications,” March 19, 2013, U.S. Patent No. 8,401,196. 2. X. Wu et al., "A secret key generation method based on CSI in OFDM FDD system," Globecom Workshops (GC Wkshps). IEEE, 2013, pp. 1297-1302. 3. H. Taha and E. Alsusa, "Secret key exchange using private random precoding in MIMO FDD and TDD systems," IEEE Trans. Veh. Technol., vol. 66, no. 6, pp. 4823-4833, 2016. 4. O. Gungor, F. Chen, and C. E. Koksal, "Secret key generation from mobility," Globecom Workshops (GC Wkshps). IEEE, 2011, pp. 874-878. 5. Badawy et al., "Secret key generation based on AoA estimation for low SNR conditions," 81st Veh.Technol.Conf.(VTC Spring).IEEE, 2015, pp. 1–7. 6. K. Lin et al., "Secret key generation based on 3D spatial angles for UAV communications," Wireless Commun.Netw.Conf.(WCNC).IEEE, 2021, pp. 1–6. 7. B. Liu, A. Hu, and G. Li, "Secret key generation scheme based on the channel covariance matrix eigenvalues ​​in FDD systems," IEEE Commun. Lett., vol. 23, no. 9, pp. 1493-1496, 2019. 8. G. Li et al., "Constructing reciprocal channel coefficients for secret key generation in FDD systems," IEEE Commun. Lett., vol. 22, no. 12, pp. 2487–2490, 2018. 9. J. Zhang et al., "A new frontier for IoT security emerging from three decades of key generation relying on wireless channels," IEEE Access, vol. 8, pp. 138-406–138-446, 2020. 10. J. Hu et al., "Secrecy analysis for orthogonal time frequency space scheme based uplink LEO satellite communication," IEEE Wireless Commun. Lett., vol. 10, no. 8, pp. 1623-1627, 2021. 11. Z. Tie et al., "Security performance analysis for an OTFS-based joint unicast-multicast streaming system," IEEE Trans. Commun., vol. 70, no. 10, pp. 6764–6777, 2022. 12. J. Sun, Z. Wang, and Q. Huang, "Secure precoded orthogonal time frequency space modulation," 13th Int. Conf. Wireless Commun. Signal Process. (WCSP). IEEE, 2021, pp. 1-5. 13. W. Liang et al., "Underlying security transmission design for orthogonal time frequency space (OTFS) modulation," Sensors, vol. 22, no. 20, pp. 7919, 2022. [Explanation of symbols]

[0043] 10a Device A 10b Device B A Antenna PU Processing Unit WC Wireless Channel I Unauthorized User

Claims

1. 1. A computer-implemented key generation method for secure wireless communication between at least two devices, comprising: designing a delay Doppler grid and determining pilot symbol locations; converting the delayed Doppler pilot signal to the time domain on both devices; transmitting time domain pilot signals to each other by the devices and converting the pilot signals to the delay Doppler domain by the devices; acquiring delay Doppler values ​​at both devices; obtaining an index of the delayed Doppler value at both devices; obtaining and quantizing fractional delay Doppler values ​​at both devices; Including, The index and the quantized fractional delay and Doppler values ​​are converted to binary representations for use as security keys.

1. A computer-implemented key generation method comprising:

2. 10. The method of claim 1 further comprising the step of determining whether the system is a frequency division duplex system or a time division duplex system.

3. 3. The method according to claim 1 or 2, characterized in that the transmitting of the converted pilot signals is performed simultaneously.

4. 3. The method of claim 1, wherein the converted pilot signal is first transmitted to one of the devices from another of the devices, and a delay Doppler value is obtained at the receiving device, and thereafter a pilot signal is transmitted to a transmitting device, and the delay Doppler value is obtained at the transmitting device.

5. The method of claim 1, characterized in that the index of the delay Doppler value is obtained by a channel estimation framework method or framework.

6. 2. The method of claim 1, wherein the dimensions of the grid in both directions are calculated according to at least one of the following: available bandwidth, number of available subcarriers, subcarrier spacing, and transmission duration.

7. 2. The method of claim 1, wherein the conversion of the delay Doppler domain to the time domain is performed by an inverse symplectic Fourier transform followed by a Heisenberg transform.

8. 2. The method of claim 1, wherein the conversion of the time domain to the delay-Doppler domain is performed by a Wigner transform followed by a symplectic Fourier transform.

9. 10. The method of claim 1, further comprising applying information matching to eliminate key mismatches.

10. 10. The method of claim 1, further comprising applying privacy amplification to increase the randomness of the generated key.

11. A system comprising means for carrying out the steps of the method according to any one of claims 1 to 10.

12. A computer program comprising instructions which, when said program is executed by a computer, cause said computer to perform the steps of the method according to any one of claims 1 to 11.

13. A computer readable medium storing the computer program of claim 12.

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