Dual-Layer Optical Security Framework for Cryptogram Camouflage Using Circular Harmonic Components

Abstract

Protecting confidential information requires not only preventing unauthorized access to encrypted data but also concealing the very existence of the protected information. In this work, we propose a computational dual-layer optical security framework that integrates optical encryption and steganographic camouflage into a unified strategy. The proposed method is based on a 4F optical architecture and employs two two-dimensional private keys: a phase-only key represented through Circular Harmonic Components (CHC) and a periodic amplitude mask acting as a second secret key. Their combined action generates visually diverse steganograms from encrypted RGB images while preserving the correct recovery of the original information by authorized users. Unlike conventional optical encryption methods that produce easily recognizable cryptograms, the proposed approach disguises the encrypted information within camouflage patterns, providing an additional layer of protection before any decryption process is attempted. Numerical simulations demonstrate successful encryption, camouflage, and image recovery while showing that different steganographic appearances can be generated by modifying the private key and the periodic-mask parameters. Furthermore, a prospective optical implementation based on a Mach--Zehnder interferometer and digital holographic recording is presented, providing a feasible path toward future experimental realization. The proposed methodology is introduced as a proof of concept of the dual-layer optical security framework; a comprehensive cryptanalytic evaluation is beyond the scope of this first study and is left for future work.