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Electronics Letters

Randomness evaluation of key generation based on optical OFDM system in visible light communication networks

Yahya Mohammed Al-Moliki, Mohammed T. Alresheedi, Yahya Al‐Harthi

Published Oct 12, 2017• 12 citations
Publisher

Abstract

Recently, the authors proposed a physical‐layer key generation scheme for optical orthogonal frequency division multiplexing (OFDM) techniques in an indoor scenario. The key generation protocol exploits bipolar and real‐valued optical OFDM samples to create confidential keys. It determines a chunk of cyclic prefix samples positioned in the space of small channel impact to generate the confidential keys during the session duration. This key‐generation approach offers strong computational security to counter passive eavesdroppers and key creation on the fly, with zero bit‐mismatch rates. In this Letter, the authors evaluate the randomness of the confidential keys produced from the recently proposed key‐generation protocol to validate if the keys are truly random. The authors apply a statistical test suite of the National Institute of Standards and Technology to test randomness. The results demonstrate that the keys generated from the proposed key generation system pass all the tests. The results also demonstrate that the proposed key generation system provides uncorrelated keys with an approximately equal probability of bits (discrete uniform distribution) on an average, which yields a high security system against statistical attacks.

DOI
10.1049/el.2017.3525

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Recently, the authors proposed a physical‐layer key generation scheme for optical orthogonal frequency division multiplexing (OFDM) techniques in an indoor scenario. The key generation protocol exploits bipolar and real‐valued optical OFDM samples to create confidential keys. It determines a chunk of cyclic prefix samples positioned in the space of small channel impact to generate the confidential keys during the session duration. This key‐generation approach offers strong computational security to counter passive eavesdroppers and key creation on the fly, with zero bit‐mismatch rates. In this Letter, the authors evaluate the randomness of the confidential keys produced from the recently proposed key‐generation protocol to validate if the keys are truly random. The authors apply a statistical test suite of the National Institute of Standards and Technology to test randomness. The results demonstrate that the keys generated from the proposed key generation system pass all the tests. The results also demonstrate that the proposed key generation system provides uncorrelated keys with an approximately equal probability of bits (discrete uniform distribution) on an average, which yields a high security system against statistical attacks.
This letter improves the confidentiality of visible light communication links by proposing a robust key-generation mechanism for optical orthogonal frequency division multiplexing (OFDM) systems in an indoor environment. In this letter, we propose to generate keys from the bipolar OFDM samples at the output of optical OFDM systems. We suggest to assign a part of cyclic prefix samples located in the region of small channel effect for keys generation during session period. The proposed scheme generates keys for medium access control (MAC) sublayer and physical layer. It provides high computational security against passive eavesdroppers in the physical level, because each signal frame is encrypted by a different key. So, the encryption in MAC level can be turned off without any risk in security. This setting can enhance the system throughput. Also, the implemented method achieves zero bit disagreement rates with key generation on the fly.
Physical layer key generation from the wireless channel is an emerging area of interest to provide confidentiality and authentication. One of the main challenges in this domain is to increase the length of the secret key while maintaining its randomness and uniformity. In this work, new dimensions for wireless channel-based key generation are proposed for orthogonal frequency division multiplexing (OFDM) systems. The novel perspective of the proposed work lies in the generation of key bits not only from the magnitudes of OFDM subchannels as it has conventionally been done but also from the number and positions of those subchannels whose channel gains are above the mean of the respective subblock. The effectiveness of the proposed algorithms is evaluated in terms of key generation rate and key mismatch rate. Additionally, a statistical test suite offered by the National Institute of Standards and Technology is used to evaluate the randomness of the generated key bits. It is shown in the simulation results that the involvement of the proposed dimensions can double the key generation rate compared to conventional algorithms.
The ability to exchange keys between users is vital in any wireless based security system. A key generation technique which exploits the randomness of the wireless channel is a promising alternative to existing key distribution techniques, e.g., public key cryptography. In this paper, a secure key generation scheme based on the subcarriers' channel responses in orthogonal frequency-division multiplexing (OFDM) systems is proposed. We first implement a time-variant multipath channel with its channel impulse response modelled as a wide sense stationary (WSS) uncorrelated scattering random process and demonstrate that each subcarrier's channel response is also a WSS random process. We then define the X% coherence time as the time required to produce an X% correlation coefficient in the autocorrelation function (ACF) of each channel tap, and find that when all the channel taps have the same Doppler power spectrum, all subcarriers' channel responses has the same ACF as the channel taps. The subcarrier's channel response is then sampled every X% coherence time and quantized into key bits. All the key sequences' randomness is tested using National Institute of Standards and Technology (NIST) statistical test suite and the results indicate that the commonly used sampling interval as 50% coherence time cannot guarantee the randomness of the key sequence.
Information is regarded as a resource with highest organizational value. Its confidentiality, integrity and authenticity are important for any organization. The broadcast nature of wireless medium makes communication vulnerable to security attacks such as eavesdropping, non-repudiation, denial of service and more. Hence, prior to transmission of information, a secret key is securely exchanged between sender and receiver. Conventional key generation algorithms work at the application layer. However, they suffer from computational overheads and require a reliable third party. Moreover, when system grows complex, these methods start failing considerably. To encounter these issues, a novel key exchange mechanism is proposed which works at the physical layer. The proposed method is based on the concept of self-jamming and exploits the properties of Orthogonal Frequency Division Multiplexing (OFDM). The simulation results show that the proposed scheme has a low Bit Error Rate (BER) for the receiver and high BER for the eavesdropper. It has also been shown that the number of attempts that eavesdropper has to make to guess the correct key are large, thereby decreasing its probability to decode the correct key.
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.
This paper presents a key generation system derived from the channel response of individual subcarrier in orthogonal frequency-division multiplexing (OFDM) systems. Practical aspects of the security were investigated by implementing our key generation scheme on a wireless open-access research platform (WARP), which enables us to obtain channel estimation of individual OFDM subcarriers, a feature not currently available in most commercial wireless interface cards. Channel response of individual OFDM subcarrier is usually a wide sense stationary random process, which allows us to find the optimal probing period and maximize the key generation rate. The implementation requires cross layer design as it involves interaction between physical and MAC layer. We have experimentally verified the feasibility and principles of key generation, and also evaluated the performance of our system in terms of randomness, key generation rate and key disagreement rate, which proves that OFDM subcarrier's channel responses are valid for key generation.