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Abstract Physical Layer Security (PLS) is an emerging paradigm employed to enhance wireless network security without relying on higher-layer encryption techniques. PLS enables legitimate users to exchange confidential messages over a wireless medium in the presence of adversaries, by utilizing the main properties and characteristics of the wireless channel. Traditionally, security in wireless networks has been addressed separately from the physical layer due to its uncontrollable random nature. However, with the massive advances in computational capabilities, classical security techniques are becoming less secure and the need for new schemes is becoming more crucial. As a result, more and more research is directed towards studying, understanding and exploiting the highly random nature of wireless networks. This paper provides a comprehensive survey on various OFDM-based PLS techniques that target popular security services namely, key generation and distribution, data confidentiality, authentication, integrity and availability. With this survey, readers can have a better understanding of the PLS techniques present in the literature, their current limitations, challenges and countermeasures, in addition to future research directions in this area. [ABSTRACT FROM AUTHOR]

Non-Orthogonal Multiple Access (NOMA) has recently emerged as a promising multiple access technique for current and future mobile communication networks. Unlike conventional multiple access schemes, NOMA exploits the power domain to service a large number of users at different power levels, using the same time–frequency resources. However, this technology suffers from major security threats since users are able to decode the messages of other paired users utilizing the same resources. In this paper, we propose an efficient and lightweight cipher scheme for NOMA systems at the physical layer. Unlike previous schemes in the literature, the proposed solution combines cryptography and Physical Layer Security (PLS) to provide robust security at minimum cost by adopting a structure that requires a single round with a single operation. Moreover, it is generic in the sense that any simple cipher operation such as permutation, substitution, phase shuffling, or pseudo-random masking, can be utilized in order to secure the underlying NOMA frame symbols. Also, we propose a dynamic key derivation scheme that benefits from the dynamic properties of wireless channels. Simulation results and cryptanalysis show that the proposed solution achieves the desired security level and strikes a good balance between performance and security level. [ABSTRACT FROM AUTHOR]