Abstract
The development of reliable and efficient techniques for protecting modern communications systems becomes a very active research point which stimulates major challenges in the twenty-first century. Several encryption schemes, including chaos-based encryption systems, have been proposed for this purpose. In this paper, we design a new hybrid technique based on asymmetrically clipped optical orthogonal frequency-division multiplexing (ACO-OFDM) and discrete memristive chaos for physical layer encryption and watermarking (PL-EW). The proposed technique is secured in the underlying physical layer of visible light communication (VLC) systems. The hybrid PL-EW ACO-OFDM technique uses two-stage encryption process to modulate both order and values of pixels in the plain image. Moreover, the introduced hybrid technique achieves the authentication property via employing two-dimensional discrete wavelet transform for the digital image watermarking process in encrypted images. A new suggested two-dimensional hyperchaotic modular cascaded memristive (2D HC-MCM) map is proposed and employed as an enhanced chaos generator capable of overcoming the observed deficiencies in similar discrete chaos systems. The proposed 2D HC-MCM map extends the secret space of original memristive map by a factor of 100. The positive Lyapunov exponents (LEs) of 2D HC-MCM map are 10 times greater than the corresponding LEs in conventional memristive map, which indicates that the complexity of chaotic attractors is boosted. The 15 statistical tests of NIST SP 800-22 are applied to examine the randomness quality of the generated chaotic sequences. The bit error rate (BER) of the proposed secure system is studied over the dispersive VLC channel. The results show that all statistical tests are passed for wide range of secret parameters, and a 10(-4) BER is achievable at SNR = 18 dB. The best extracted digital watermark image with an ideal NCC can be achieved at SNR = 24 dB. Finally, a plethora of security attacks is applied to verify the immunity of hybrid PL-CEW ACO-OFDM technique against possible types of attacks. It is shown that the proposed scheme can resist brute force, differential, statistical, and different signal processing attacks.