Secret key generation (SKG) from the randomness provided by random channels is currently considered as one way to improve security in wireless communications at the physical layer level. However, the relation between the performance of SKG schemes and the characteristics of the radio channel has been moderately investigated. In this work, we evaluate the security performance on the basis of a simple channel model based on scatterers distributed around terminals, which enables going beyond the common assumption of spatial stationarity between the legitimate terminal and the eavesdropper. This performance is assessed both from information theory metrics and from a practical key extraction algorithm. Owing to the model flexibility, we evaluate the impact of several major channel characteristics such as the distribution and density of scatterers or the existence of a dominant LOS path.
Secret key generation (SKG) from the randomness provided by random channels is currently considered as one way to improve security in wireless communications at the physical layer level. However, the relation between the performance of SKG schemes and the characteristics of the radio channel has been moderately investigated. In this work, we evaluate the security performance on the basis of a simple channel model based on scatterers distributed around terminals, which enables going beyond the common assumption of spatial stationarity between the legitimate terminal and the eavesdropper. This performance is assessed both from information theory metrics and from a practical key extraction algorithm. Owing to the model flexibility, we evaluate the impact of several major channel characteristics such as the distribution and density of scatterers or the existence of a dominant LOS path.
Nowadays, the security of ubiquitous wireless communications becomes more and more a crucial requirement. Even though data is widely protected via symmetric ciphering keys, a well-known difficulty is the generation and distribution of such keys. In the recent years therefore, a set of works have addressed the exploitation of inherent characteristics of the fading propagation channel for security. In particular, secret keys could be generated from the wireless channel, considered as a shared source of randomness, available merely to a pair of communicating entities. ln the present dissertation, we are interested in the approach of secret key generation (SKG) from wireless channels, especially in relating the radio channel properties to the generated keys quality. We first develop a stochastic channel model, focusing on the security with respect to the eavesdropper side, which shows a residual channel memory weil beyond a few wavelengths distance (spatially nonstationary scenarios). Then, we analyze the channel degrees of freedom (DoF) and their impact on the SKG performance in different channel conditions, especially by considering more realistic channels in both outdoor and indoor environments (respectively through simulated ray tracing data and through measurements). The results show that, even for moderately wide band (such as standardized in IEEE 802.11), the sole frequency DOF or its association with the spatial DOF is often enough for generating long keys, provided an efficient quantization method of the complex channel coefficients is used.
In the recent years, a set of works have addressed inherent characteristics of the fading propagation channel in an information-theoretic framework oriented towards security. In particular, for cryptographic purposes, secure key bits can be extracted from reciprocal radio channels, seen as a shared source of randomness between any two entities. In this paper we intend to assess the impact of true radio channel features on the security performance, by quantizing the complex channel coefficients into discrete key bits. To this end, indoor channel measurements were performed and investigated in different scenarios, e.g. LOS/NLOS condition, narrowband (NB) as well as wide band (WB) targeting OFDM systems. Secret key robustness is firstly studied for the legitimate terminals in terms of key bit disagreement ratio and key randomness, and secondly by considering an eavesdropper in a wide set of positions around these terminals and by evaluating the difference between the generated keys. A simplified channel model is also analyzed in comparison with the measured channels, as regards the characteristics of generated key bits.
A few years ago, physical layer based techniques have started to be considered as a way to improve security in wireless communications. A well known problem is the management of ciphering keys, both regarding the generation and distribution of these keys. A way to alleviate such difficulties is to use a common source of randomness for the legitimate terminals, not accessible to an eavesdropper. This is the case of the fading propagation channel, when exact or approximate reciprocity applies. Although this principle has been known for long, not so many works have evaluated the effect of radio channel properties in practical environments on the degree of randomness of the generated keys. To this end, we here investigate indoor radio channel measurements in different environments and settings at either 2.4625 GHz or 5.4 GHz band, of particular interest for WIFI related standards. Key bits are extracted by quantizing the complex channel coefficients and their randomness is evaluated using the NIST test suite. We then look at the impact of the carrier frequency, the channel variability in the space, time, and frequency degrees of freedom used to construct a long secret key, in relation to the nature of the radio environment such as the LOS/NLOS character.
Physical layer security is a method to ensure the confidentiality of a wireless communication from encryption keys exploiting the randomness of the reciprocal propagation channel between a pair of legitimate users, Alice and Bob. This confidentiality is achieved owing to the decorrelation between these channels and that experienced by a third terminal (Eve), acting as an eavesdropper. In this work, we evaluate the secret key capacity of a simple channel model, based on a disc of scatterers. The model allows to consider any distance between Bob and Eve within the disc, thus is not limited to a spatial stationarity, and is suitable to investigate the impact on the security of multiple antennas.
The emergence of Internet of things (IoT) applications brings the challenge of finding lightweight schemes for secret key distribution. A promising solution coming from the physical layer is the so called secret key generation (SKG) from shared randomness. SKG allows two communicating parties to extract the shared randomness already present in wireless channels. This work investigates the achievable SKG rates using received signal strength (RSS) as a key generation parameter. A multi-path scenario is considered and the probability density function of the RSS in different channel conditions is evaluated. Next, through a numerical evaluation, the SKG rates are derived in the form of mutual information (MI) estimates, using a 3GPP standard channel model. The simulations are performed for different values of bandwidth and delay spread. We demonstrate that while both parameters have similar impact on how multi-path components are resolved, their effect on the MI is opposite.
The main objective of this chapter is to study explicit key extraction techniques and algorithms for the security of radio communication. After some recalls on the main processing steps (Figure 19.1(a)) and on theoretical results relevant to the radio wiretap model (Figure 19.1(b)), we detail recent experimental results on randomness properties of real field radio channels. Furthermore, we detail a practical implantation of secret key generation (SKG) schemes, based on the Channel Quantization Alternate (CQA) algorithm helped with channel decorrelation techniques, into modern public networks such as WiFi and radio-cells of fourth generation (LTE, long-term evolution). Finally, through realistic simulations and real field experiments of radio links, we analyze the security performance of the implemented SKG schemes, and highlight their significant practical results and perspectivesfor future implantations into existing and next-generation radio standards.