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.
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.
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.
Device-to-device communication is increasingly important for emerging wireless applications, including the Internet of Things and industry mobile networks. To establish a secure communication channel between multiple legitimate devices, key agreement is an essential first step. Physical layer channel information is a promising technology for achieving communication security by generating a shared channel key. In this paper, we propose an efficient and random method for generating channel keys based on channel state information (CSI). Firstly, we preprocess the available subcarriers to reduce the correlation of adjacent subcarriers. Secondly, we propose a novel quantization process to generate random and secure channel keys. The part consists of two phases: the quantization phase and the inconsistency removal phase. In the quantization stage, CSI sub carriers are grouped into small blocks, and appropriate thresholds are generated. Then, wireless users quantize the CSI subcarriers into initial bit streams of 0 and 1 with different thresholds. In the inconsistency removal phase, we design an error correction mechanism where wireless users exchange the discarded index sequences in the initial bit streams to achieve key sequence consistency. We implement the proposed scheme using off-the-shelf wireless devices and evaluate its performance. The experimental results show that each CSI packet can produce 30 bits, which have passed the NIST randomness tests.
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.
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.
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.
Due to the reciprocity of wireless channels, the communication parties can directly extract the shared key from channel. This solution were verified through several schemes. However, in real situations, channel sampling of legitimate transceivers might be impacted by noises and other interferences, which makes the channel states obtained by initiator and responder might be obvious different. The efficiency and even availability of physical layer key generation are thus reduced. In this paper, we propose a lightweight and efficient physical layer key generation scheme, which extract shared secret keys from channel state information (CSI). To improve the key generation process, the discrete cosine transform (DCT) is employed to reduce differences of channel states of legitimate transceivers. Then, these outputs are quantified and encoded through multi-bit adaptive quantization(MAQ) quantizer and gray code to generate binary bit sequence, which can greatly reduce the bit error rate. Moreover, the low density parity check (LDPC) code and universal hashing functions are used to achieve information reconciliation and privacy amplifification. By adding preprocessing methods in the key generation process and using the rich information of CSI, the security of communications can be increased on the basis of improving the key generation rate. To evaluate this scheme, a number of experiments in various real environments are conducted. The experimental results show that the proposed scheme can effificiently generate shared secret keys for nodes and protect their communication.