Optical digital dual image encryption scheme based on fast Fourier symmetry fusion and bit-level compression

Abstract Digital images serve as vital components of contemporary communication systems, yet their prevalence intensifies privacy risks. To ensure secure transmission, image encryption technology has become a crucial solution. This paper thoroughly examines the dual-image encryption problem and introduces an innovative hybrid scheme that integrates optical and digital image encryption. The scheme consists of two main parts. In the first part, the Fast Fourier Symmetry Fusion Encryption Method(FFSFEM) is proposed, which involves processing two plaintext images using the Fast Fourier Transform(FFT) and then fusing them. The resulting fused images are then subjected to an inverse Fast Fourier Transform(iFFT) followed by bit-level compression, yielding two images, the real part and the imaginary part. This part can be operated in a 4f optical system. In the second part, the pixels of both the real and imaginary images are diffused and confused, leading to the generation of the encrypted images. The results are: correlation coefficient is almost 0, average information entropy = 7.9993 bits, average NPCR = 99.6127%, average UACI = 33.5510% and it is able to resist selective plaintext attack. The proposed algorithm is verified to have strong security and encryption performance in terms of simulation experiments and security analysis.