The wireless secret key agreement offers information theoretic secrecy with potential for low energy implementations. However, the presented works have concentrated mainly on wireless technologies such as 802.11 or 802.15.4, which are suitable for small scale local networks. This paper gives the first insights on how to establish LoRa based secret key agreement for low-power widea area networks (LPWAN). In particular: 1) characterization of LoRa parameter influence on the key agreement 2) comparison between available channel probing methods and 3) evaluation of several wireless scenarios with off-the-shelf LoRa devices, have been conducted to reveal the optimal hardware settings and the key generation performance. The main results indicate that the instantaneous RSSI measurement capability leads in most cases to lower key disagreement and higher key entropy. A further outcome shows that strong secret keys can be extracted from LoRa node-gateway communication, even when the devices are stationary.
The wireless secret key agreement offers information theoretic secrecy with potential for low energy implementations. However, the presented works have concentrated mainly on wireless technologies such as 802.11 or 802.15.4, which are suitable for small scale local networks. This paper gives the first insights on how to establish LoRa based secret key agreement for low-power widea area networks (LPWAN). In particular: 1) characterization of LoRa parameter influence on the key agreement 2) comparison between available channel probing methods and 3) evaluation of several wireless scenarios with off-the-shelf LoRa devices, have been conducted to reveal the optimal hardware settings and the key generation performance. The main results indicate that the instantaneous RSSI measurement capability leads in most cases to lower key disagreement and higher key entropy. A further outcome shows that strong secret keys can be extracted from LoRa node-gateway communication, even when the devices are stationary.
Physical-layer security (PLS) schemes use the randomness of the channel parameters, namely, channel state information (CSI) and received signal strength indicator (RSSI) to generate the secret keys. There has been limited work in PLS schemes in long-range (LoRa) wide-area networks (LoRaWANs) which hinder their widespread application. Limitations observed in existing studies include the requirement of high correlation between channel parameter measurements for secret key generation in the proposed schemes and the evaluation of the schemes has only been done in either fully indoor or outdoor environments. The real-world wireless sensor networks (WSNs) and LoRa use cases might not meet both requirements thus making the current PLS schemes inappropriate for these systems. By considering the limitations found in existing PLS schemes, this article proposes LoRA-LiSK, a practical and efficient shared secret key generation scheme for LoRa networks. Our proposed LoRa-LiSK scheme consists of several preprocessing techniques (timestamp matching, two sample Kolmogorov–Smirnov tests, and a Savitzky–Golay filter), multilevel quantization, information reconciliation using Bose–Chaudhuri–Hocquenghem (BCH) codes, and finally, privacy amplification using secure hash algorithm SHA-2. The LoRa-LiSK scheme is extensively evaluated on real WSN/IoT devices in practical application scenarios: 1) indoor to outdoor and 2) LoRa static and mobile outdoor links. It outperforms existing schemes by generating keys with channel parameter measurements of low correlation values (0.2–0.6), while still essentially achieving high key generation rates, and low key disagreement rates (10%–20%). The scheme updates a key in approximately 1 h using an application profile with high transmission rate compared to 3 h reported by existing works while still respecting the duty cycle regulation. It also incurs less communication overhead compared to the existing works.
Low-Power Wide Area Networks (LPWAN) has emerged as the dominant open specification in recent years due to its ability to offer affordable connectivity to the low-power devices distributed over large geographical areas. However, security issues have not been fully addressed in LPWAN specifications, especially, key distribution and key management. Physical layer key generation, which exploits wireless channel reciprocity and randomness to generate secure keys, has attracted considerable attention in recent years. In this paper, we exploit the physical layer key generation problem in LPWAN communication and present a distributed and lightweight key generation scheme for Long Range (LoRa) based network. It explores the shared randomness extracted from measured RSSI (Received Signal Strength Indicator) as consensus information to generate secure keys. To negotiate the RSSI signal as a bidirectional consistent key sequence, we propose a novel level-crossing quantization algorithm with an improved Cascade key agreement protocol to improve the key generation rate, as well as to avoid information leakage during transmission. We implement the proposed physical layer key generation scheme in a LoRa network prototype. Then we conduct extensive experiments in stationary and mobile indoor environments to evaluate the efficiency of the proposed key generation scheme. Experimental results show that its achievable key rate can reach 29.5% in stationary scenario and 35.5% in mobile scenario. Its key generation rate can exceed 1 bit/s with a lightweight implementation on the LoRa network prototype. For the 128-bit key sequence, it passes the the NIST suite of statistical tests.
Physical layer key generation that exploits reciprocity and randomness of wireless fading channels has attracted considerable attention in recent years. Despite much research efforts in this field, the problem of wireless key generation at long distance and low data rate remains unknown and has not been studied. In this paper, we conduct extensive experiments and analysis in real indoor and outdoor environments to explore the feasibility of wireless key generation for long range (LoRa)-based network. Our experimental results show that: 1) the low transmission rate will lead to low channel reciprocity which makes wireless key generation significantly challenging and 2) when the requirement of high reciprocity is fulfilled, two nodes can generate the same secret key even when they are far away from each other (a few kilometers). Building on the strengths of existing secret key extraction approaches, we present LoRa-Key, the first complete key establishment protocol for LoRa network by exploring the shared randomness extracted from measured received signal strength indicator. LoRa-Key employs a number of signal processing techniques to improve key generation rate significantly. Moreover, we propose a novel compressive sensing-based reconciliation framework to reduce mismatch rate. Experimental results show that LoRa-Key can achieve key establishment rates of 18 bit/s in stationary scenario and 31 bit/s in mobile scenario. To the best of our knowledge, this is the first work that studies key generation protocol for LoRa network.
Physical layer key generation that exploits reciprocity and randomness of wireless fading channels has attracted considerable attention in recent years. Despite much research efforts in this field, the problem of wireless key generation at long distance and low data rate remains unknown and has not been studied. In this paper, we conduct extensive experiments and analysis in real indoor and outdoor environments to explore the feasibility of wireless key generation for Long Range Wide Area Network (LoRaWAN). Based on the results, we present LoRa-Key, the first complete key establishment protocol for LoRaWAN by exploring the shared randomness extracted from measured Received Signal Strength Indicator (RSSI). LoRa-Key employs a number of signal processing techniques to improve key generation rate significantly. Experimental results show that LoRa-Key can achieve key establishment rates of 13 bit/s in stationary scenario and 21 bit/s in mobile scenario. To the best of our knowledge, this is the first work that studies key generation protocol for LoRaWAN.
Physical layer key generation technology which leverages channel randomness to generate secret keys has attracted extensive attentions in long range (LoRa)-based networks recently. We in this paper develop a software-defined radio (SDR) based LoRa communications platform using GNU Radio on universal software radio peripheral (USRP) to implement and evaluate typical physical layer key generation schemes. Thanks to the flexibility and configurability of GNU Radio to extract LoRa packets, we are able to obtain the fine-grained channel frequency response (CFR) through LoRa preamble based channel estimation for key generation. Besides, we propose a low-complexity preprocessing method to enhance the randomness of quantization while reducing the secret key disagreement ratio. The results indicate that we can achieve 367 key bits with a high level of randomness through just a single effective channel probing in an indoor environment at a distance of 2 meters under the circumstance of a spreading factor (SF) of 7, a preamble length of 8, a signal bandwidth of 250 kHz, and a sampling rate of 1 MHz.
There is a growing interest in physical layer security. Recent work has demonstrated that wireless devices can generate a shared secret key by exploiting variations in their channel. The rate at which the secret bits are generated, however, depends heavily on how fast the channel changes. As a result, existing schemes have a low secrecy rate and are mainly applicable to mobile environments. In contrast, this paper presents a new physical-layer approach to secret key generation that is both fast and independent of channel variations. Our approach makes a receiver jam the signal in a manner that still allows it to decode the data, yet prevents other nodes from decoding. Results from a testbed implementation show that our method is significantly faster and more accurate than state of the art physical-layer secret key generation protocols. Specifically, while past work generates up to 44 secret bits/s with a 4% bit disagreement between the two devices, our design has a secrecy rate of 3-18 Kb/s with 0% bit disagreement.