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Conference on Information Sciences and Systems

Secret key generation through OFDM multipath channel

Yanpei Liu, Stark Christiaan Draper, A.M. Sayeed

Published Mar 1, 2011• 24 citations
Publisher

Abstract

We analyze the fundamental limits of key generation and describe an implementation based on error correcting codes. We show that key extraction based on channel coefficients significantly outperforms key extraction based on received signal strength indicators (RSSI). The development in this paper is based on an IEEE 802.11a orthogonal frequency-division multiplexing (OFDM) model and We demonstrate that it is feasible to use the sampled channel coefficients in OFDM as the key source. The key extraction problem is cast as a Slepian-Wolf coding and decoding problem. We construct regular and irregular forms of binary and non-binary low-density parity check (LDPC) codes to prototype our key extraction.

DOI
10.1109/ciss.2011.5766103

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We analyze the fundamental limits of key generation and describe an implementation based on error correcting codes. We show that key extraction based on channel coefficients significantly outperforms key extraction based on received signal strength indicators (RSSI). The development in this paper is based on an IEEE 802.11a orthogonal frequency-division multiplexing (OFDM) model and We demonstrate that it is feasible to use the sampled channel coefficients in OFDM as the key source. The key extraction problem is cast as a Slepian-Wolf coding and decoding problem. We construct regular and irregular forms of binary and non-binary low-density parity check (LDPC) codes to prototype our key extraction.
We design and analyze a method to extract secret keys from the randomness inherent to wireless channels. We study a channel model for the IEEE 802.11a orthogonal frequency-division multiplexing channel. We analyze the fundamental limits of key generation for this model and describe an implementation based on error correcting codes. We study key extraction based both on channel state information (CSI) and on received signal strength indicators (RSSI). Due to the reduction in the degree-of-freedom when going from CSI to RSSI, the rate of key extraction based on CSI is far higher than that based on RSSI. This suggests that making CSI information available to higher layers would greatly assist in key generation. We prototype a key generation system based on low-density parity-check codes. We describe the implementation and performance of two systems: one based on binary LDPC codes and the other (useful at higher signal-to-noise ratios) based on four-ary LDPC codes.
We design and analyze a method to extract secret keys from the randomness inherent to wireless channels. We study a channel model for a multipath wireless channel and exploit the channel diversity in generating secret key bits. We compare the key extraction methods based both on entire channel state information (CSI) and on single channel parameter such as the received signal strength indicators (RSSI). Due to the reduction in the degree-of-freedom when going from CSI to RSSI, the rate of key extraction based on CSI is far higher than that based on RSSI. This suggests that exploiting channel diversity and making CSI information available to higher layers would greatly benefit the secret key generation. We propose a key generation system based on low-density parity-check (LDPC) codes and describe the design and performance of two systems: one based on binary LDPC codes and the other (useful at higher signal-to-noise ratios) based on four-ary LDPC codes.
Abstract—We design and analyze a method to extract secret keys from the randomness inherent to wireless channels. We study a channel model for multipath wireless channel and exploit the channel diversity in generating secret key bits. We compare the key extraction methods based both on entire channel state information (CSI) and on single channel parameter such as the received signal strength indicators (RSSI). Due to the reduction in the degree-of-freedom when going from CSI to RSSI, the rate of key extraction based on CSI is far higher than that based on RSSI. This suggests that exploiting channel diversity and making CSI information available to higher layers would greatly benefit the secret key generation. We propose a key generation system based on low-density parity-check (LDPC) codes and describe the design and performance of two systems: one based on binary LDPC codes and the other (useful at higher signal-to-noise ratios) based on four-ary LDPC codes. Index Terms—Common randomness, secret key generation, channel diversity, LDPC codes, Slepian-Wolf decoder I.
Key generation from the randomness of wireless channels is a promising technique to establish a secret cryptographic key securely between legitimate users. This paper proposes a new approach to extract keys efficiently from the channel responses of individual orthogonal frequency-division multiplexing (OFDM) subcarriers. The efficiency is achieved by: 1) fully exploiting randomness from time and frequency domains and 2) improving the cross-correlation of the channel measurements. Through the theoretical modeling of the time and frequency autocorrelation relationship of the OFDM subcarrier's channel responses, we can obtain the optimal probing rate and use multiple uncorrelated subcarriers as random sources. We also study the effects of non-simultaneous measurements and noise on the cross-correlation of the channel measurements. We find that the cross-correlation is mainly impacted by noise effects in a slow fading channel and use a low-pass filter to reduce the key disagreement rate and extend the system's working signal-to-noise ratio range. The system is evaluated in terms of randomness, key generation rate, and key disagreement rate, verifying that it is feasible to extract randomness from both time and frequency domains of the OFDM subcarrier's channel responses.
Securing wireless communication remains challenging in dynamic mobile environments due to the shared nature of wireless medium and lacking of fixed key management infrastructures. Generating secret keys using physical layer information thus has drawn much attention to complement traditional cryptographic-based methods. Although recent work has demonstrated that Received Signal Strength (RSS) based secret key extraction is practical, existing RSS-based key generation techniques are largely limited in the rate they generate secret bits and are mainly applicable to mobile wireless networks. In this paper, we show that exploiting the channel response from multiple Orthogonal Frequency-Division Multiplexing (OFDM) subcarriers can provide fine-grained channel information and achieve higher bit generation rate for both static and mobile cases in real-world scenarios. We further develop a Channel Gain Complement (CGC) assisted secret key extraction scheme to cope with channel non-reciprocity encountered in practice. Our extensive experiments using WiFi networks in both indoor as well as outdoor environments demonstrate that our approach can achieve significantly faster secret bit generation rate at 60 ~ 90bit/packet, and is resilient to malicious attacks identified to be harmful to RSS-based techniques including predictable channel attack and stalking attack.
In this paper, a novel physical layer key generation method for extracting secret key from mutual channel information in orthogonal frequency division multiplexing (OFDM) systems has been proposed. Firstly, a well-designed data extraction process has been introduced to reduce the redundancy and inconsistency of channel state information (CSI). After that, a new quantization method using gray code is proposed. Furthermore, an associated method is designed to reduce key error rate (KER). With these improvements, higher key generation rate (KGR) can be obtained compared to existing methods. Finally, available secret keys have been generated after information reconciliation and privacy amplification. The proposed method has been analyzed and verified in long term evolution advanced (LTE-A) systems and the generated secret keys have passed randomness test.