Secrecy, Covertness and Authentication in Wireless Communications

In this chapter, we introduce some typical wireless communication systems and networks, such as two-hop relay systems, ad hoc networks and cellular networks, followed by the introduction of the fundamentals of the physical layer security (PLA) technology in secure wireless communication, covert wireless communication, and authentication.

The PLS technology is highly promising for implementing secure communication in wireless systems due to its advantages of easy deployment, low complexity, and everlasting secrecy. In this chapter, we provide secure communication schemes based on typical PLS techniques like beamforming, precoding, link selection, as well as cooperative jamming. In Sect. 2.1, we show how to design a secure beamforming scheme to maximize the secrecy rate of two-way relay systems. In Sect. 2.2, we also focus on the two-way relay systems and present a secure precoding scheme to maximize the secrecy energy efficiency (SEE). In Sect. 2.3, we investigate effective link selection policies for two-hop cooperative wireless networks. The security-delay tradeoff issue in a two-hop wireless system based on the relay selection technique is studied in Sect. 2.4, followed by a sight-based cooperative jamming (SCJ) scheme for millimeter-wave (mmWave) systems in Sect. 2.5.

While Chap. 2 shows the great potential of the PLS technology in ensuring secure wireless communication, this chapter introduces how the PLS technology can be applied to achieve covert communication in wireless systems. In particular, we focus on two-hop relay systems and examine the covertness performance of such systems under various PLS techniques. In Sect. 3.1, we investigate the interplay between legitimate nodes and malicious wardens in a two-hop two-way relay system and show the covertness performance with an emphasis on the scaling law results of covert throughput. Different from the relays considered in Sect. 3.1, Sect. 3.2 focuses on the case of FD relays that can switch between the FD mode and the HD mode. Since the timeliness of CSI is vital for covert communication, Sect. 3.3 therefore explores the impact of outdated CSI on the covertness performance of the relay systems.

Physical layer authentication (PLA) represents another promising application of the PLS technology in wireless communications, aiming at establishing trust among communicating entities. The fundamentals and categories of PLA have been introduced in Chap. 1.​2.​3. This chapter further discusses PLA and presents concrete implementations of passive RFF-based PLA, channel-based PLA, and hybrid PLA. In Sect. 4.1, we exemplify how to use multiple radiometric features to develop an RFF-based PLA scheme in direct-sequence spread spectrum (DSSS) communication systems. In Sect. 4.2, we give an illustrative example of instantaneous channel-based PLA in massive MIMO systems. In Sect. 4.3, a hybrid PLA scheme in MIMO systems is provided, which is based on the combination of the channel-based feature in Sect. 4.2 and a radiometric feature named phase noise.

Due to the advantages of low computational complexity, easy implementation in a distributed manner and no need to distribute/manage secret keys, applying the PLS technology to protect transmission security in various wireless communication systems has been attracting considerable academic attention recently. Existing studies on the design of PLS-based schemes mainly focus on either the single-hop (point-to-point) or two-hop relay communication systems. Although these studies have made great progress, they are not applicable to multi-hop network scenarios. In many cases, wireless nodes (devices) adopt short-range communication due to power limitations. Hence, data of a source may need to be forwarded by several intermediate nodes to reach its destination when the distance between the source and destination is far. In this context, it is essential to leverage a routing scheme to establish the route (path) for end-to-end data delivery. However, the PLS-oriented routing design for multi-hop wireless communication systems still remains largely uninvestigated and needs to be addressed carefully. This chapter introduces the PLS-based secure routing design. In Sect. 5.1, we present a security/QoS-aware route selection mechanism in multi-hop wireless ad hoc networks under different forwarding strategies. In Sect. 5.2, we show the PLS-based secure routing schemes that can achieve optimal security-QoS tradeoffs. In Sect. 5.3, we investigate the secure routing design taking into account the selfishness of cooperative jammers. The common performance metrics used in this chapter include SOP and connection outage probability (COP), where the former defines the probability that the SINR at one or more eavesdroppers is above a fixed threshold and the latter represents the probability that the SINR at the intended receiver is below a required threshold. SOP and COP serve as the metrics of security and QoS of the communication, respectively.

This chapter provides a summary of the whole book and presents some challenges that may hinder the real-world application of PLS techniques. Furthermore, we introduce some future directions that may be inspiring for subsequent research in this area.