Communications, wired and wireless, have integrated various cryptographic techniques to ensure privacy and counter surveillance. These techniques have been integrated in most of the network layers, except for the physical layer. This physical layer has, thus far, dealt with schemes such as source coding, channel coding, and (de)modulation, to enable the transmission of data in a reliable and efficient manner. The emergence of physical layer security extends the functionalities at the physical layer to include secure communication, aiming at the transmission of a signal that can only be correctly retrieved by the intended receiver. Therefore, the goals of physical layer security align with cryptographic schemes utilized at the other network layers. From the extensive study of physical layer security schemes, we have observed that there is a knowledge gap regarding certain security principles practiced by cryptographers and the experts within physical layer security, causing many physical layer security schemes to be impractical for standardization and the wide-scale integration into information and communication technologies. This paper describes a variety of security principles and concepts, practiced by cryptographers, and of importance to physical layer security experts. We aim to raise the awareness of these security principles and concepts to experts within the field of physical layer security to improve the practicality, standardization, and integration potential of the design of future physical layer security schemes.
Communications, wired and wireless, have integrated various cryptographic techniques to ensure privacy and counter surveillance. These techniques have been integrated in most of the network layers, except for the physical layer. This physical layer has, thus far, dealt with schemes such as source coding, channel coding, and (de)modulation, to enable the transmission of data in a reliable and efficient manner. The emergence of physical layer security extends the functionalities at the physical layer to include secure communication, aiming at the transmission of a signal that can only be correctly retrieved by the intended receiver. Therefore, the goals of physical layer security align with cryptographic schemes utilized at the other network layers. From the extensive study of physical layer security schemes, we have observed that there is a knowledge gap regarding certain security principles practiced by cryptographers and the experts within physical layer security, causing many physical layer security schemes to be impractical for standardization and the wide-scale integration into information and communication technologies. This paper describes a variety of security principles and concepts, practiced by cryptographers, and of importance to physical layer security experts. We aim to raise the awareness of these security principles and concepts to experts within the field of physical layer security to improve the practicality, standardization, and integration potential of the design of future physical layer security schemes.
To ensure confidentiality, today's communications are encrypted under the notion of computational security, using hard mathematical problems to build ciphers that apparently cannot be cracked in a useful time. However, as these constructions are not agnostic to technological advances, some of these problems may be solved efficiently with future technologies, e.g. quantum computing. In wireless networks, physical layer security emerges as a post-quantum security solution that promises to mitigate these threats. This concept of secrecy exploits the physical properties of the wireless channel to encode information so that a certain degree of statistical independence between the message and the cyphertext is observed by the eavesdropper. This notion of secrecy allows building cryptosystems that are agnostic to the computing capabilities of the attacker, being widely accepted as one of the strongest notions of secrecy created so far. The objective of this chapter is to overview the concept of physical layer security and understand how its integration could be done in future wireless networks. For that purpose, the information-theoretical framework grounding the concept is introduced, and some basic design approaches are presented. These include PHY key generation methods, secure beamforming techniques, and cooperative jamming constructions. The mechanisms to enable the integration of these technologies in future 5G and beyond networks are discussed last.
Wireless communications are naturally exposed to important security risks due to their broadcast nature. In contrast with wired communications, no physical medium is isolating the transmission surroundings to a specific path. Traditional methods to reach the goals of communications security rely on algorithms at protocol stack level, which are based on mathematically derived cryptographic protocols. With the tremendous proliferation of wireless devices, and the increase in computational power available for decryption, traditional cryptographic measures may be compromised. To protect communications at the lowest level, physical layer (PHY) security methods have been proposed recently. These techniques aim to ensure secure communications by exploiting the unique characteristics of the physical medium between communicating nodes, effectively reducing the decryption capabilities of an eavesdropper to intercept transmissions. This thesis explains within a general framework the most important PHY layer security schemes. First we explore approaches which utilize the knowledge of the unique channel between communicating nodes to distort a transmitted signal with various kinds of randomizations, in such a way that the intended receivers are unaffected by the distortion, but any other observer will be exposed to it. These techniques, however, introduce several trade-offs between transmission resources and the effectiveness in achieving secrecy. Of particular interest for this investigation is a class of methods which can be referred to as "security enhancing techniques", in which minimal priors about the potential eavesdroppers locations and capabilities are assumed. In this thesis, a wave-based approach to the communication secrecy problem is introduced. An interesting perspective is provided by studying the relation between electromagnetic theory and information theory, the so-called electromagnetic information theory. This allows to properly identify the unavoidable limitations imposed by the laws of electromagnetics to our ability to communicate securely. The proposed model can be extended to the analysis of different signal distortion methodologies and different channel conditions. The resulting approach is highly relevant to the study of PHY layer security methods since it is physically fundamental as well as architecture independent, which leads to a consolidating point of view of the secrecy problem. In addition, the thesis presents computer simulation results which shed insight on the security possibilities and limitations of three different security scenarios, which are termed MISO (multiple-input, single-output) (with single eavesdropper), MISOME (multiple-input, single-output, multiple eavesdropper), and MIMOME (multiple-input, multiple-output, multiple-eavesdropper).
The broadcast nature of wireless communication systems makes wireless transmission extremely susceptible to eavesdropping and even malicious interference. Physical layer security technology can effectively protect the private information sent by the transmitter from being listened to by illegal eavesdroppers, thus ensuring the privacy and security of communication between the transmitter and legitimate users. Thus, the main design goal of physical layer security is to increase the performance difference between the link of the legitimate receiver and that of the eavesdropper using well-designed transmission schemes. The development of mobile communication presents new challenges to physical layer security research. This paper provides a survey of the physical layer security research on various promising mobile technologies from secure key generation and keyless techniques, including secure key generation, directional modulation (DM), spatial modulation (SM), covert communication, and intelligent reflecting surface (IRS)-aided communication. Finally, the future topics and the unresolved technical challenges are presented in physical layer security for mobile communications.
The fast development of wireless networks, which are intrinsically exposed to eavesdropping, has created a growing concern for confidentiality. While classical cryptographic schemes require a key provided by the end-user, physical-layer security leverages the randomness of the physical communication medium as a source of secrecy. The main benefit of physical-layer security techniques is their relatively low cost and their ability to combine with any existing security mechanisms. This dissertation provides an analysis including the theoretical study of the two-way wiretap channel to obtain a better insight into how to design coding mechanisms, practical tests with experimental systems, and the design of actual codes. From a theoretical standpoint, the study confirms the benefits of combining several multi-user coding techniques including cooperative jamming, coded cooperative jamming and secret key generation. For these different mechanisms, the trade-off between reliability, secrecy and communication rate is clarified under a stringent strong secrecy metric. Regarding the design of practical codes, spatially coupled LDPC codes, which were originally designed for reliability, are modified to develop a coded cooperative jamming code. Finally, a proof-of-principle practical wireless system is provided to show how to implement a secret key generation system on experimental programmable radios. This testbed is then used to assess the realistic performance of such systems in terms of reliability, secrecy and rate.
Security in wireless networks has traditionally been considered to be an issue to be addressed separately from the physical radio transmission aspects of wireless systems. However, with the emergence of new networking architectures that are not amenable to traditional methods of secure communication such as data encryption, there has been an increase in interest in the potential of the physical properties of the radio channel itself to provide communications security. Information theory provides a natural framework for the study of this issue, and there has been considerable recent research devoted to using this framework to develop a greater understanding of the fundamental ability of the so-called physical layer to provide security in wireless networks. Moreover, this approach is also suggestive in many cases of coding techniques that can approach fundamental limits in practice and of techniques for other security tasks such as authentication. This paper provides an overview of these developments.
Physical layer security (PHY-security) takes the advantages of channel randomness nature of transmission media to achieve communication confidentiality and authentication. Wiretap coding and signal processing technologies are expected to play vital roles in this new security mechanism. PHY-security has attracted a lot of attention due to its unique features and the fact that our daily life relies heavily on wireless communications for sensitive and private information transmissions. Compared to conventional cryptography that works to ensure all involved entities to load proper and authenticated cryptographic information, PHY-security technologies perform security functions without considering about how those security protocols are executed. In other words, it does not require to implement any extra security schemes or algorithms on other layers above the physical layer. This survey introduces the fundamental theories of PHY-security, covering confidentiality and authentication, and provides an overview on the state-of-the-art works on PHY-security technologies that can provide secure communications in wireless systems, along with the discussions on challenges and their proposed solutions. Furthermore, at the end of this paper, the open issues are identified as our future research directions.