Three-dimensional image hierarchical encryption method based on structured light holography and chained iris keys

This paper proposes a three-dimensional image hierarchical encryption method based on structured light holography and chained iris keys, aiming to address issues in the existing 3D image encryption techniques, such as low decryption quality, insufficient key security, inconvenient key management, and lack of hierarchical access control. The method first divides the 3D image into equidistant slices along the depth direction, generates encrypted structured light using a custom-designed structured light phase mask, and computes the structured light hologram for each slice layer via an iterative angular spectrum algorithm. Subsequently, user iris images are captured, and after preprocessing and feature extraction, user-specific chaotic phase masks are generated through a piecewise linear chaotic map, serving as keys for the hierarchical encryption. On this basis, a chained hierarchical encryption strategy is adopted, where the hologram of each level is coupled with the corresponding user's chaotic mask and the hologram from the previous level for the encryption, forming a dependent ciphertext sequence. During decryption, users must undergo iris authentication to obtain the chaotic key corresponding to their access level, followed by sequential chained decryption and optical reconstruction, thereby achieving identity- and authority-based hierarchical information access. Simulation experiments demonstrate that the method ensures high-quality 3D reconstruction while exhibiting high key sensitivity and robustness against noise, occlusion, and statistical attacks. Furthermore, the multi-parameter design in the structured light phase mask further expands the key space and enhances system security. This study provides a secure, practical, and manageable solution for the confidential transmission and hierarchical management of sensitive 3D visual data, with potential applications in fields such as medical imaging, military simulation, and virtual reality.