A Diffusion-Only Image Encryption System for High-Speed Applications

The widespread and growing utilisation of digital images has made image encryption a crucial concern, garnering significant attention from researchers. Regrettably, the development and study of fast encryption schemes for colour images are currently lacking. This paper proposes a specifically designed colour image encryption system for high-speed applications, utilising only diffusion techniques. The proposed technique employs a set of five Piece-wise Linear Chaotic Maps (PWLCM) with different first values and control factors to execute the image encryption operation. The SHA-256 hashing is employed for the initialization of first values and control factors in PWLCM system. The technique involves initially separating the colour image into its three colour components. Subsequently, the three components are horizontally concatenated. Next, the generation of three key images is achieved by employing the three PWLCM systems, each with distinct key parameters. Subsequently, these three key images are concatenated together. Furthermore, the concatenated outputs are partitioned into blocks with dimensions of $(1 \times 3)$. The process involves performing a bit-XORing diffusion process on the concatenated outputs of the selected blocks of the colour component and the key image. The block selection operation is performed using two distinct PWLCM systems. The diffused blocks are ultimately merged to produce the ciphertext. Based on the analysis on security and experimental outputs, it has been determined, the described method successfully encrypts the color photos of different sizes while ensuring their security.