The use of wireless networks for communication has grown significantly in recent times, and continues to develop further. The broadcast nature of wireless communications makes them susceptible to a wide variety of security attacks. Unlike traditional solutions, which usually handle security at the application layer, the primary concern of this dissertation is to analyse and develop solutions for secure communication using channel coding techniques at the physical-layer. \nThe topic of physical layer authenticated encryption using high rate key generation through shared randomness is investigated in this work. First, a physical layer secret key generation scheme is discussed exploiting channel reciprocity in wireless systems. In order to address the susceptibility of this family of schemes to active attacks, a novel physical layer authentication encryption protocol is presented along with its extension to multi-node networks in the presence of active adversaries. Unlike previous work in the area of generating secret keys through shared randomness, it is demonstrated that the proposed scheme is semantically secure with respect to chosen plaintext and chosen cipher text attacks. \nSecondly, in order to increase the rate in bits per seconds at which agreed cryptographic keys are been generated, a multi-level quantization algorithm with public feedback is discussed. It is demonstrated that the proposed scheme is superior to direct information distillation approaches and can substantially increase the key generation rates even at low and medium SNRs. Furthermore, the employment of this low-overhead feedback at the information distillation process can largely simplify the information reconciliation process. \nThe proposed secret key generation schemes are tested for randomness such as required for cryptographic keys. The validation test is perfomed with the aid of National Institute of Standards and Technology (NIST) statistical test suite. The P-values obtained in each of the test carried out indicates that the key sequence generated by our algorithm is random.
The use of wireless networks for communication has grown significantly in recent times, and continues to develop further. The broadcast nature of wireless communications makes them susceptible to a wide variety of security attacks. Unlike traditional solutions, which usually handle security at the application layer, the primary concern of this dissertation is to analyse and develop solutions for secure communication using channel coding techniques at the physical-layer. \nThe topic of physical layer authenticated encryption using high rate key generation through shared randomness is investigated in this work. First, a physical layer secret key generation scheme is discussed exploiting channel reciprocity in wireless systems. In order to address the susceptibility of this family of schemes to active attacks, a novel physical layer authentication encryption protocol is presented along with its extension to multi-node networks in the presence of active adversaries. Unlike previous work in the area of generating secret keys through shared randomness, it is demonstrated that the proposed scheme is semantically secure with respect to chosen plaintext and chosen cipher text attacks. \nSecondly, in order to increase the rate in bits per seconds at which agreed cryptographic keys are been generated, a multi-level quantization algorithm with public feedback is discussed. It is demonstrated that the proposed scheme is superior to direct information distillation approaches and can substantially increase the key generation rates even at low and medium SNRs. Furthermore, the employment of this low-overhead feedback at the information distillation process can largely simplify the information reconciliation process. \nThe proposed secret key generation schemes are tested for randomness such as required for cryptographic keys. The validation test is perfomed with the aid of National Institute of Standards and Technology (NIST) statistical test suite. The P-values obtained in each of the test carried out indicates that the key sequence generated by our algorithm is random.
The topic of physical layer authenticated encryption using high rate key generation through shared randomness is investigated in this work. First, a physical layer secret key generation scheme is discussed exploiting channel reciprocity in wireless systems. In order to address the susceptibility of this scheme to active attacks, a novel physical layer authentication encryption protocol is presented along with its extension to multi-node networks in the presence of active adversaries. Secondly, in order to increase the key generation rate, a multi-level quantization algorithm with public feedback is discussed. It is demonstrated that the proposed scheme is superior to direct information distillation approaches and can substantially increase the key generation rates even at low and medium SNRs.
Due to the broadcast nature of wireless channels, wireless communication is vulnerable to eavesdropping, message modification, and node impersonation. Securing the wireless communication requires the shared secret keys between the communicating entities. Traditional security schemes rely on public key infrastructures and cryptographic algorithms to manage secret keys. Recently, many physical-layer-based methods have been proposed as alternative solutions for key generation in wireless networks. These methods exploit the inherent randomness of the wireless fading channel to generate secret keys while providing information-theoretical security without intensive cryptographic computations. This article provides an overview of the existing PHY-based key generation schemes exploiting the randomness of the wireless channels. Specifically, we first introduce the fundamental and general framework of the PHY-based key generation schemes and then categorize them into two classes: received-signal-strength-based and channel- phase-based protocols. Finally, we present a performance comparison of them in terms of key disagreement probability, key generation rate, key bit randomness, scalability, and implementation issues.
As an alternative and appealing approach to providing information security in wireless communication systems, secret key generation at physical layer has demonstrated its potential in terms of efficiency and reliability over traditional cryptographic methods. Without the necessity of a management centre for key distribution or reliance on computational complexity, physical layer key generation protocols enable two wireless entities to extract identical and dynamic keys from the randomness of the wireless channels associated with them.\nIn this thesis, the reliability of secret key generation at the physical layer is examined in practical wireless channels with imperfect channel state information (CSI). Theoretical analyses are provided to relate key match rate with channel's signal-to-noise ratio (SNR), degrees of channel reciprocity, and iterations of information reconciliation.\nIn order to increase key match rate of physical layer secret key generation, improved schemes in the steps of channel estimation and sample quantization are proposed respectively. In the channel estimation step, multiple observations of the wireless channels are integrated with a linear processor to provide a synthesized and more accurate estimation of the wireless channel. In the sample quantization step, a magnitude based quantization method with two thresholds is proposed to quantize partial samples, where specific quantization areas are selected to reduce cross-over errors. Significant improvements in key match rate are proven for both schemes in theoretical analysis and numerical simulations. Key match rate can even achieve 100% in both schemes with the assistance of information reconciliation process.\nIn the end, a practical application of physical layer secret key generation is presented, where dynamic keys extracted from the wireless channels are utilized for securing secret data transmission and providing efficient access control.
Modern networking technologies involve the interconnection of smart and intelligent physical objects to provide advanced services. These physical objects may be part of various network technologies like WLAN, wireless sensor network (WSN), Internet of Things (IoT), etc., and share data in wireless mode, which should be secured from threats. These physical devices possess many constraints like power, computational complexity and storage, and are required to have lightweight security algorithms. Traditionally, security is achieved by the higher layers of the communication model, which has high computational complexity and consumes more power. In this chapter, a secure-key-generation scheme from physical layer characteristics is introduced as a possible lightweight security alternative to traditional upper-layer security approaches. The proposed scheme is based on the wiretap-channel model and security is achieved by generating keys at both communicating ends independently, based on inherent common-channel characteristics like randomness. It is mainly based on the principle of spatial decorrelation and channel reciprocity for identical carrier frequency. There is no provision for sharing keys as in public-key cryptography, so physical-layer key generation is not vulnerable to threats like key leakage. The generated key at the transmitter encrypts plain text; the generated cipher is transmitted on the common channel and is decrypted at the receiver end using the key generated by the receiver. Key generation consists of fundamental blocks like channel probing and quantization followed by information reconciliation and privacy amplification. The physical-layer key generation is already a power-efficient security solution; this chapter aims to enhance this capacity further. This is done by introducing low-end signal conditioning in the channel-probing step using moving-window averaging. This solution not only improves system performance but also makes it suitable for limited- power applications. The performance of the key-generation system is characterised in terms of the bit-disagreement rate between the generated key sequences of communicating parties and the key randomness by means of the NIST statistical test suite.
Abstract: Physical layer key generation, leveraging the reciprocity and randomness of wireless fading channels, has garnered significant research interest in recent years. While theoretical studies have demonstrated its potential to generate informationtheoretically secure keys, challenges remain in translating theory into practice. This paper provides an overview of the physical layer key generation process and discusses its practical challenges. Various passive and active attacks are analyzed and evaluated through numerical studies. A new key generation scheme using random probing signals and combining usergenerated randomness with channel randomness is introduced to counteract active attacks. Numerical results demonstrate that the proposed scheme achieves higher security strength than existing schemes using constant probing signals under active attacks. Secret-key generation relying on wireless channel reciprocity is an intriguing solution as it can be efficiently implemented at the physical layer of emerging wireless communication networks, while providing information-theoretic security guarantees. In this paper, we investigate and compare the secret-key capacity based on the sampling of the entire complex channel state information (CSI) or only its envelope, the received signal strength (RSS).
Reliable communication over Wireless Body Area Networks (WBANs) is an essential aspect of Wireless Body Area Networks (WBANs) because the physiological data flows between wearable sensor nodes is sensitive data. The convectional cryptography methods usually apply a lot of computational complexity as well as energy overhead besides which they are not going to fit in the ultra-low-power WBANs. In the current paper a light-weight, energy-efficient Physical Layer Key Generation (PLKG) scheme the possibilities of which based on the native randomness and reciprocity of the wireless channel is used to generate secure symmetric keys is presented. With WBANs, there is a lot of temporal and spatial dynamics in the human body and its surrounding environment, which causes great variability in channel characteristics, in terms of Received Signal Strength Indicator (RSSI) and Channel State Information (CSI). Such physical layer parameters can be used as perfect entropy sources in generation of unique, unpredictable secret keys with whose knowledge, communication between nodes is possible and mutually exclusive only. The channel probing in the proposed framework is also robust, multi-bit quantization is performed adaptively, information reconciliation is performed through error correction codes, and privacy amplification is made through cryptographic hashing. We have developed a resilient system against bit mismatch and efficiently against passively eavesdropping, we guarantee the secrecy of the generated keys under adversary situation. With realistic WBAN models simulation and experiment validation shows that the proposed approach is capable of generating keystokes with very high key generation rate (50 bps) and a bit mismatch rate of lower than 3 percent as compared to existing schemes that solely relied on RSSI, making this protocol more secure and reliable to use. In addition, the framework meets the statistical randomness requirements specified by NIST and it does not leak mutual information to eavesdroppers. The scheme allows real-time use on resource-constrained devices, e.g., wearable medical devices and health-monitoring sensor, as it has low computational and memory overhead. The findings establish the feasibility of employing physical layer properties to achieve secure WBANs communication without any pre-shared keys or a centralized trust paradigm, thus, opening the way to scalable and privacy-preserving healthcare systems.