A Hybrid Digital and Optical Double Color Image Encryption Scheme Using a Nine-Dimensional Chaotic System

A nine-dimensional (9D) chaotic-based hybrid digital/optical Encryption (HDOE) scheme is proposed for a double color image. The 9D chaotic sequences are grouped into three independent sets, each responsible for the encryption of one of the RGB channels. Thus, the three color channels are encrypted separately, enhancing the security level and robustness of the encryption process. The digital encryption (DE) part uses fusion and scrambling and is interrupted by a chaotic color image controlled by three of the chaotic sequences, one from each set. The optical encryption (OE) part is implemented in the optical Fourier transform (FT) domain and assisted by two chaotic phase masks (CPMs) for phase-encoding operation. The color CPM is constructed by three chaotic sequences, one from each chaotic sequences sets. The proposed HDOE scheme yields very-high entropy (7.9988), which is very close to the ideal case (8).