Enhancing Underwater Optical Wireless Communication with a High Efficiency Image Encryption System

This paper presents an image encryption scheme for underwater optical wireless communication (UOWC) systems based on dynamically generated hyperchaotic S-boxes, aiming to enhance both data security and transmission performance in underwater environments. The proposed encryption approach provides strong confusion and diffusion properties and is evaluated over five Jerlov water types with different optical attenuation characteristics. Security analysis demonstrates that the encrypted images achieve information entropy values close to the ideal value of 8 (7.9925–7.9993), with very low correlation coefficients in horizontal, vertical, and diagonal directions, as well as the system achieves high values in key metrics such as the Unified Average Changing Intensity (UACI) and Number of Pixel Change Rate (NPCR), ranging from 33.42 to 33.47 and from 99.58% to 99.62%, respectively, both near their theoretical optima. In addition to improving confidentiality, the hyperchaotic encryption process decorrelates pixel intensities and redistributes image spectral content, which enhances robustness against underwater absorption and scattering effects. As a result, improved transmission performance is observed; for example, in Jerlov type I (JI) water, the effective transmission distance is extended from 16 m for plain images to 24 m for encrypted images, while the Peak Signal to Noise Ratio (PSNR) at 24 m increases from 9.25 to 20.13 dB after decryption and enhancement. These results confirm that the proposed scheme provides a dual benefit of secure and reliable image transmission in UOWC systems.