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Physical layer (PHY) security has emerged as a promising methodology for securing current and future networks that employ orthogonal frequency-division multiplexing (OFDM) technology. OFDM is the basic building block for multicarrier modulation in most contemporary networks such as vehicular ad hoc networks, Internet of Things (IoT), as well as 4G/5G systems. Most existing OFDM-based security solutions lack the notion of secrecy and dynamicity when combining a secret key with random information extracted from the physical channel. Yet, some solutions perform encryption preinverse fast Fourier transform and some postinverse fast Fourier transform, without clear guidelines concerning the impact on performance and security. In this paper, OFDM-based encryption schemes at the PHY are investigated, analyzed, and weaknesses are identified. It is shown that encryption in the frequency domain slightly …