Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

IEEE International Conference on Acoustics Speech and Signal Processing

Variable guard band construction to support key reconciliation

Alexandra Filip, Rashid Mehmood, Jon W. Wallace, Werner Henkel

Published May 1, 2014• 7 citations
Publisher

Abstract

Key reconciliation procedures are needed to correct key differences that can arise as a consequence of independent noise at the two ends of a reciprocal link. We assume a line-of-sight channel and use reconfigurable antenna elements to randomize it, such that it allows for key generation. The Linde-Buzo-Gray algorithm is employed to quantize the complex channel transfer characteristic, and adaptive guard bands, symmetric to the quantization thresholds, are further constructed. To limit the number of key errors, we ensure that only the points that fall outside the guard band interval are accepted for key generation. The steps for constructing the guard bands are presented.

DOI
10.1109/icassp.2014.6855194

Related papers

Quantization Aspects in LDPC Key Reconciliation for Physical Layer Security

Oana Graur, Nazia Islam, Alexandra Filip +1 more

For physical-layer security, key reconciliation procedures are needed to correct key differences that can arise as a consequence of independent noise at the two ends of a reciprocal link. We assume either a random link in a mobile environment or use reconfigurable antenna elements to randomize the channel, such that it allows for frequent key generation. We apply LDPC codes to reconcile the keys on both sides. In here, we derive the LLRs taking into account the underlying quantization.

•Feb 1, 2015•10 citations

A Simple Physical-Layer Key Generation for Frequency-Division Duplexing (FDD)

Werner Henkel, Maria Namachanja

Common randomness of channels offers the possibility to create cryptographic keys without the need for a key exchange procedure. Channel reciprocity for TDD (time-division duplexing) systems has been used for this purpose many times. FDD (frequency-division duplexing) systems, however, were long considered to not provide any usable symmetry. However, since the scattering transmission parameters S12and S21would ideally be the same due to reciprocity, when using neighboring frequency ranges for both directions, they would just follow a continuous curve when putting them next to each other. To not rely on absolute phase, we use phase differences between antennas and apply a polynomial curve fitting, thereafter, quantize the midpoint between the two frequency ranges with the two measurement directions. This is shown to work even with some spacing between the two bands. For key reconciliation, we force the measurement point from one direction to be in the midpoint of the quantization interval by a grid shift (or likewise measurement data shift). Since the histogram over the quantization intervals does not follow a uniform distribution, some source coding / hashing will be necessary. The key disagreement rate toward an eavesdropper was found to be close to 0.5. Additionally, when using an antenna array, a random permutation of antenna measurements can even further improve the protection against eavesdropping.

International Conference on Signal Processing and Communication Systems•Dec 13, 2021•7 citations

An Interpolated Quantized Guard Band Algorithm for Physical Layer Key Generation

Yongli An, Kun Zha, Wenfeng Song +1 more

With the continuous progress of communication technology, traditional encryption algorithms cannot meet the demands of modern wireless communication security. Secure communication based on physical layer encryption emerges as a solution. To meet the low Key Disagreement Rate (KDR) and high Key Generation Rate (KGR) requirements for physical layer key generation, this paper proposes two quantization algorithms, Improve-CQG and Interpolate-CQG, based on the Channel Quantization with Guard band (CQG) algorithm. The former divides the characteristic quantization into two phases: threshold filtering and guard band quantization, while the latter adds a step after these two phases: interpolation quantization. Compared to the CQG algorithm, the Improve-CQG algorithm enhances the granularity of filtered quantization values. The core concept of the Interpolate-CQG algorithm is to utilize threshold filtering and the rounded-off quantization values from the guard band quantization phase. The symbol information corresponding to these index values is replaced by a new interpolated symbol and inserted into the key by the agreed quantized coordinates. Simulation proves that the Interpolate-CQG is an effective quantization algorithm for the key generation with lower KDR and higher KGR than the Improve-CQA and Improve-CQG.

Intelligent and Converged Networks•Mar 1, 2025•2 citations

Adaptive Quantization for Key Generation in Low-Power Wide-Area Networks

Chen Chen, Junqing Zhang, Yingying Jennifer Chen

Physical layer key generation based on reciprocal and random wireless channels has been an attractive solution for securing resource-constrained low-power wide-area networks (LPWANs). When quantizing channel measurements, namely received signal strength indicator (RSSI), into key bits, the existing works mainly adopt fixed quantization levels and guard band parameters, which fail to fully extract keys from RSSI measurements. In this paper, we propose a novel adaptive quantization scheme for key generation in LPWANs, taking LoRa as a case study. The proposed adaptive quantization scheme can dynamically adjust the quantization parameters according to the randomness of RSSI measurements estimated by Lempel-Ziv complexity (LZ76), while ensuring a predefined key disagreement ratio (KDR). Specifically, our scheme uses pre-trained linear regression models to determine the appropriate quantization level and guard band parameter for each segment of RSSI measurements. Moreover, we propose a guard band parameter calibration scheme during information reconciliation during real-time key generation operation. Experimental evaluations using LoRa devices show that the proposed adaptive quantization scheme outperforms the benchmark differential quantization and fixed quantization with up to 2.35$\times$ and 1.51$\times$ key generation rate (KGR) gains, respectively.

arXiv:2310.07853•Oct 11, 2023•2 citations

A Simple Physical-Layer Key Generation Scheme for Power-Line Transmission

Werner Henkel, Ha Young Kim, Abderraheem M. Turjman +1 more

We have already shown in earlier publications that reciprocity of power-line channels, expressed by, e.g., S12= S21using scattering parameters, can provide the desired common randomness for physical layer key generation. We had used minima or maxima of those transfer S-parameters to select possible keys. The tree-like power-line topology with bridge taps that are imperfectly terminated, possibly just left open, provide the means to create deep notches and, of course, local maxima in between. Using those positions, however, does not work well under noise conditions and power-line channels are known for their stationary and non-stationary disturbances. Minima will just be filled by noise, maxima that are wider than the minima experience a ripple thereby making it difficult to obtain identical positions under uncorrelated noise at the legitimate users’ ends. To solve this issue, in here, we propose to instead use the amplitude values at maxima positions. Disturbances there are directly related to the noise amplitudes. High maxima and corresponding key sequences resulting from amplitude quantization of the transfer characteristic are then less error-prone. Further improvements to reduce noise effects are obvious, just like averaging measurements, smoothing over frequency, or just only accepting measurements above certain thresholds. Quantization of amplitudes is carried out in log domain and mapping to bit patterns is realized in a cyclic fashion together with Gray coding. Key reconciliation is realized by shifting measurements into the middle of quantization intervals.

IEEE International Symposium on Power Line Communications and Its Applications (ISPLC)•Oct 26, 2021•9 citations

Quantization for Physical Layer Security

Oana Graur, Nazia Islam, Werner Henkel

We propose a multi-level CSI quantization and key reconciliation scheme for physical layer security. The noisy wireless channel estimates obtained by the users first run through a transformation, prior to the quantization step. This enables the definition of guard bands around the quantization boundaries, tailored for a specific efficiency and not compromising the uniformity required at the output of the quantizer. Our construction results in an better key disagreement and initial key generation rate trade-off when compared to other level-crossing quantization methods.

IEEE Globecom Workshops (GC Wkshps)•Dec 1, 2016•8 citations
Key reconciliation procedures are needed to correct key differences that can arise as a consequence of independent noise at the two ends of a reciprocal link. We assume a line-of-sight channel and use reconfigurable antenna elements to randomize it, such that it allows for key generation. The Linde-Buzo-Gray algorithm is employed to quantize the complex channel transfer characteristic, and adaptive guard bands, symmetric to the quantization thresholds, are further constructed. To limit the number of key errors, we ensure that only the points that fall outside the guard band interval are accepted for key generation. The steps for constructing the guard bands are presented.
Common randomness of channels offers the possibility to create cryptographic keys without the need for a key exchange procedure. Channel reciprocity for TDD (time-division duplexing) systems has been used for this purpose many times. FDD (frequency-division duplexing) systems, however, were long considered to not provide any usable symmetry. However, since the scattering transmission parameters S12and S21would ideally be the same due to reciprocity, when using neighboring frequency ranges for both directions, they would just follow a continuous curve when putting them next to each other. To not rely on absolute phase, we use phase differences between antennas and apply a polynomial curve fitting, thereafter, quantize the midpoint between the two frequency ranges with the two measurement directions. This is shown to work even with some spacing between the two bands. For key reconciliation, we force the measurement point from one direction to be in the midpoint of the quantization interval by a grid shift (or likewise measurement data shift). Since the histogram over the quantization intervals does not follow a uniform distribution, some source coding / hashing will be necessary. The key disagreement rate toward an eavesdropper was found to be close to 0.5. Additionally, when using an antenna array, a random permutation of antenna measurements can even further improve the protection against eavesdropping.
With the continuous progress of communication technology, traditional encryption algorithms cannot meet the demands of modern wireless communication security. Secure communication based on physical layer encryption emerges as a solution. To meet the low Key Disagreement Rate (KDR) and high Key Generation Rate (KGR) requirements for physical layer key generation, this paper proposes two quantization algorithms, Improve-CQG and Interpolate-CQG, based on the Channel Quantization with Guard band (CQG) algorithm. The former divides the characteristic quantization into two phases: threshold filtering and guard band quantization, while the latter adds a step after these two phases: interpolation quantization. Compared to the CQG algorithm, the Improve-CQG algorithm enhances the granularity of filtered quantization values. The core concept of the Interpolate-CQG algorithm is to utilize threshold filtering and the rounded-off quantization values from the guard band quantization phase. The symbol information corresponding to these index values is replaced by a new interpolated symbol and inserted into the key by the agreed quantized coordinates. Simulation proves that the Interpolate-CQG is an effective quantization algorithm for the key generation with lower KDR and higher KGR than the Improve-CQA and Improve-CQG.
Physical layer key generation based on reciprocal and random wireless channels has been an attractive solution for securing resource-constrained low-power wide-area networks (LPWANs). When quantizing channel measurements, namely received signal strength indicator (RSSI), into key bits, the existing works mainly adopt fixed quantization levels and guard band parameters, which fail to fully extract keys from RSSI measurements. In this paper, we propose a novel adaptive quantization scheme for key generation in LPWANs, taking LoRa as a case study. The proposed adaptive quantization scheme can dynamically adjust the quantization parameters according to the randomness of RSSI measurements estimated by Lempel-Ziv complexity (LZ76), while ensuring a predefined key disagreement ratio (KDR). Specifically, our scheme uses pre-trained linear regression models to determine the appropriate quantization level and guard band parameter for each segment of RSSI measurements. Moreover, we propose a guard band parameter calibration scheme during information reconciliation during real-time key generation operation. Experimental evaluations using LoRa devices show that the proposed adaptive quantization scheme outperforms the benchmark differential quantization and fixed quantization with up to 2.35×\times× and 1.51×\times× key generation rate (KGR) gains, respectively.
We have already shown in earlier publications that reciprocity of power-line channels, expressed by, e.g., S12= S21using scattering parameters, can provide the desired common randomness for physical layer key generation. We had used minima or maxima of those transfer S-parameters to select possible keys. The tree-like power-line topology with bridge taps that are imperfectly terminated, possibly just left open, provide the means to create deep notches and, of course, local maxima in between. Using those positions, however, does not work well under noise conditions and power-line channels are known for their stationary and non-stationary disturbances. Minima will just be filled by noise, maxima that are wider than the minima experience a ripple thereby making it difficult to obtain identical positions under uncorrelated noise at the legitimate users’ ends. To solve this issue, in here, we propose to instead use the amplitude values at maxima positions. Disturbances there are directly related to the noise amplitudes. High maxima and corresponding key sequences resulting from amplitude quantization of the transfer characteristic are then less error-prone. Further improvements to reduce noise effects are obvious, just like averaging measurements, smoothing over frequency, or just only accepting measurements above certain thresholds. Quantization of amplitudes is carried out in log domain and mapping to bit patterns is realized in a cyclic fashion together with Gray coding. Key reconciliation is realized by shifting measurements into the middle of quantization intervals.
We propose a multi-level CSI quantization and key reconciliation scheme for physical layer security. The noisy wireless channel estimates obtained by the users first run through a transformation, prior to the quantization step. This enables the definition of guard bands around the quantization boundaries, tailored for a specific efficiency and not compromising the uniformity required at the output of the quantizer. Our construction results in an better key disagreement and initial key generation rate trade-off when compared to other level-crossing quantization methods.