Abstract
Recently, physical-layer encryption was featured as a favorable security method for visible light communications (VLCs). Generally, orthogonal frequency-division multiplexing (OFDM) is the key structure unit for the multicarrier modulation of up-to-date networks, such as vehicular ad hoc networks, 4G/5G systems, and the Internet of Things (IoT). This study proposes a robust lightweight channel-independent (LCI) physical-layer encryption method based on optical OFDM to strengthen the confidentiality of VLC systems. The method is suitable for resource-restricted machines, such as IoT systems. With the help of the hashing and stream cipher schemes, the random characteristics of the input data are exploited to create dynamic cipher keys renewed at every frame. The proposed method achieves a threefold encryption operation that involves substitution, phase encryption for frequency-domain OFDM subcarriers, and permutation for time-domain OFDM subcarriers. The results indicate that the proposed method improves the VLC confidentiality against various attacks, such as statistical attacks, known/chosen plaintexts, and brute-force attacks. Aside from improving confidentiality, the proposed method decreases the peak-to-average power ratio of the signal, enhances the bit-error-rate efficiency, and decreases the communication latency.