Chaos Fractal Digital Image Encryption Transmission in Underwater Optical Wireless Communication System

This study introduces a novel image cryptosystem designed to improve security and reliability within underwater optical wireless communication (UOWC) systems particularly for water bodies that exhibits higher absorption and scattering coefficients. An image encryption scheme, characterized by high security, and consists of a chaotic iteration of dragon fractal shapes (ChDrFr). The system performance is assessed across five distinct water types, each exhibiting unique optical properties. For enhancing the quality of encrypted images received, median and high-pass filters are utilized. To test the ability of this new algorithm to ward off different types of attacks, numerical simulation is applied. Specifically, a correlation coefficient of approximately zero is witnessed between the original images and those generated by encryption. The optimum values for information entropy and unified average changed intensity (UACI) are almost reached for the encrypted images. A comparison is undertaken between different encryption methods and the one proposed in this paper, depending on ChDrFr. Results show that the proposed encryption scheme yields better results and achieves much securer encrypted images, when compared to the images encrypted by other encryption algorithms. Additionally, the encrypted images show enhancement in the underwater transmission distance with 6% for Pure Sea (PS) and Clear Ocean (CL), 4% for Coastal Sea (CS), 0.9% for Harbor I (HI), and 0.8% for Harbor II (HII). Moreover, the utilization of filters results in improvement in the Structured Similarity Index (SSIM), Peak-Signal-to-Noise-Ratio (PSNR), and Signal-to-Noise-Ratio (SNR).