Optical encryption and lossless carrier hiding of underwater images based on Fourier holography and a 5D chaotic...

The rapid advancement of underwater imaging technology has generated massive amounts of image data. How to securely store and reliably transmit such data under stringent resource constraints have become a key challenge in the field of marine information. Existing underwater image encryption schemes primarily rely on digital encryption, which typically produces noise-like encrypted images that are prone to attracting attention from potential attackers during transmission and storage. Moreover, current underwater image encryption schemes often lack systematic validation of robustness and reliability in practical communication scenarios. To address these issues, this paper proposes an optical encryption and lossless carrier hiding of underwater images based on Fourier holography and a 5D chaotic system. The proposed scheme employs a five-dimensional chaotic system to generate encryption keys, offering a large key space of up to 10²¹⁰, enabling single-channel optical encryption of color underwater images and thereby reducing optical hardware requirements. Furthermore, the encrypted optical images achieve lossless carrier hiding, effectively mitigating the issue of drawing attention from potential attackers during transmission and storage. Finally, the robustness and reliability are validated through communication simulations using orthogonal frequency-division multiplexing (OFDM) and generalized frequency-division multiplexing (GFDM), addressing the lack of systematic validation in existing underwater image encryption schemes. Experimental results demonstrate that the proposed scheme not only inherits the advantages of high initial-value sensitivity from chaotic systems and the physical security inherent to Fourier holographic optical encryption but also achieves lossless carrier-based concealment of optical images. This offers a novel solution, to our knowledge, for underwater image transmission characterized by high security, strong robustness, and enhanced stealth.