An image encryption scheme combining chaos-memory cellular automata and weighted histogram

This paper presents a new symmetric scheme for enciphering digital images. The proposal is based on the combination of chaos and cellular automata (CA) under the scenarios of one round enciphering/deciphering and permutation–diffusion architecture. All the generated key-streams in the proposed cryptosystem are based on the use of an improved one-dimensional (1D) chaotic system [i.e., logistic–tent system (LTS)] with excellent chaotic properties. These key-streams are related to both the secret key and the characteristics of the plain image. Before applying the encryption process, one pixel of the plain image at a random position is overwritten by inserting the weighted histogram value as a new measure to represent the plain image’s features, this pixel withholds the encryption routine and further will be used to guarantee the resistance to known/chosen plain image attacks (CPA secure). In the confusion phase, a bit-level permutation is adopted with the generated one-time key-streams using an improved 1D chaotic system. This strategy of shuffling is handled in which besides to the modification of each pixel’s position, its value is also changed, to further render the achievement of both confusion and diffusion possible within just this phase. The diffusion phase is divided into two subphases: In the first one, the value of each pixel is changed sequentially by means of an improved one-dimensional chaotic system, to fasten the diffusion process and spread the influence of a single bit over the others, and in the second subphase, two-dimensional reversible memory cellular automata are associated with quadtree decomposition strategy and applied to the output of the first subphase, to enhance both the security and the diffusion effect of the cryptosystem. Security analysis shows the capacity of the proposed scheme to resist the commonly known attacks besides to its competitive speed that traces its suitability for practical image encryption.