This paper introduces a novel physical layer secure communication technology based on wireless channel direct encryption to enhance the encryption strength of the information source. Unlike traditional methods of key generation based on the reciprocity of the wireless channel, which typically involve quantizing the wireless channel and then negotiating keys, resulting in two completely identical bit strings generated as encryption keys for upper-level cryptographic algorithms between legitimate communication parties, this paper's approach quantizes the quantized bits of the wireless channel characteristics of both legitimate parties and directly encrypts the information source bits by using a designed lightweight encryption/decryption algorithm. Compared to traditional approaches, this paper's method avoids the key consultation process for physical layer key distribution, expanding the scenarios for the use of physical layer keys. Moreover, it can work independently at the same time with the upper layer cryptography to enhance the encryption strength. Through experimental verification, it has been confirmed that, in cases where the channel error rate during information transmission is less than 5*10^-2, this model can achieve an average reception accuracy of 99.6% for legitimate communicators while ensuring that eavesdroppers cannot decrypt. This approach can also compatible with upper-layer security encryption/decryption algorithms at each layer of the OSI, e.g., data link layer and network layer, offering extensive application prospects.
This paper introduces a novel physical layer secure communication technology based on wireless channel direct encryption to enhance the encryption strength of the information source. Unlike traditional methods of key generation based on the reciprocity of the wireless channel, which typically involve quantizing the wireless channel and then negotiating keys, resulting in two completely identical bit strings generated as encryption keys for upper-level cryptographic algorithms between legitimate communication parties, this paper's approach quantizes the quantized bits of the wireless channel characteristics of both legitimate parties and directly encrypts the information source bits by using a designed lightweight encryption/decryption algorithm. Compared to traditional approaches, this paper's method avoids the key consultation process for physical layer key distribution, expanding the scenarios for the use of physical layer keys. Moreover, it can work independently at the same time with the upper layer cryptography to enhance the encryption strength. Through experimental verification, it has been confirmed that, in cases where the channel error rate during information transmission is less than 5*10^-2, this model can achieve an average reception accuracy of 99.6% for legitimate communicators while ensuring that eavesdroppers cannot decrypt. This approach can also compatible with upper-layer security encryption/decryption algorithms at each layer of the OSI, e.g., data link layer and network layer, offering extensive application prospects.
The traditional wireless communication security technology is based on cryptography at the network layer, which exploits computational complexity to make it difficult to crack to achieve encryption. With the ongoing advancement of computing power, computational security may be difficult to maintain. From the viewpoint of information theory, physical layer security technology is an essential instrument for integrating security and communication. This paper mainly studies the quantization steps in the key generation technology of wireless communication physical layer. In this paper, a quantization scheme with extremely low implementation complexity is proposed for key generation. Firstly, utilizing the reciprocity and randomness of the wireless channel, the communication parties conduct channel measurements to collect channel state information (CSI) and study the improvement of CSI extraction by incorporating intelligent reflection surfaces. Then, the proposed hybrid quantization scheme makes full use of CSI and quantizes the CSI and its phase information to obtain key bits. Numerical results show that the proposed scheme improves the quality of key generation and avoids information leakage during transmission, and passes the NIST randomness test.
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.
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.
In recent years, physical layer security has become one of the core technologies for wireless communication system security. Physical layer encryption is based on the inherent reciprocity, time-varying, spatial uniqueness and unpredictability of wireless communication systems to generate keys, which are naturally unforgeable and steganography-proof. However, the research of physical layer key generation technology also faces many challenges, such as the problem of poor key generation performance due to signal interference, the problem of lower randomness and slower key generation rate in quasi-static channel environment, and the problem of lower key consistency between two legitimate communication parties due to the existence of channel estimation errors; this paper provides a systematic explanation of the traditional model of key generation for wireless channels and a typical solution for this series of problems. In this paper, the traditional model of wireless channel key generation is systematically explained, and the typical solutions to this series of problems are studied, analysed and compared in terms of performance.
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.
Physical layer encryption is a promising solution to provide transmission security for Internet-of-Things (IoT). To realize physical layer encryption, channel state information (CSI) as a random source to generate secret keys should be exploited. The reciprocity of wireless channel between legitimate communication nodes which is typically assumed for time division duplex (TDD) systems, is of critical importance to ensure the consistency in generated keys at two nodes. However, in practical TDD systems, due to the asynchronous measurement of CSI, the receiver noise and the the difference in hardware, etc., the reciprocity of channel measurements between legitimate parties is hard to be guaranteed, which makes physical layer key generation approach infeasible. To address this issue, we propose a wireless key generation scheme based on deep learning techniques. Firstly, a feature extraction network, which consists of two auto-encoders trained jointly, is developed to extract the common feature from the different yet correlated channel observations at two legitimate nodes, which will be used as the source to generate keys. Then a quantizer with an adaptive guard band width is devised to output a binary secret-key sequence from the feature vector. Numerical results show that the proposed scheme achieves remarkable improvement in terms of key disagreement rate (KDR) and key generation rate (KGR) compared existing counterparts in the literature.