While designing and developing encryption algorithms for text and images, the main focus has remained on security. This has led to insufficient attention on the improvement of encryption efficiency, enhancement of hyperchaotic sequence randomness, and dynamic DNA-based S-box. In this regard, a new symmetric block cipher scheme has been proposed. It uses dynamic DNA-based S-box connected with MD5 and a hyperchaotic system to produce confusion and diffusion for encrypting color images. Our

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... d scheme supports various size color images. It generates three DNA based Sboxes for substitution namely DNA_1_s-box, DNA_2_s-box and DNA_3_sbox, each of size 16 × 16. Next, the 4D hyperchaotic system followed by MD5 is employed in a novel way to enhance security. The three DNAbased S-boxes are generated from real DNA sequences taken from National Center for Biotechnology Information (NCBI) databases and are dependent on the mean intensity value of an input image, thus effectively introducing content-based confusion. Finally, Conservative Site-Specific Recombination (CSSR) is applied on the output DNA received from DNA based S-boxes. The experimental results indicate that the proposed encryption scheme is more secure, robust, and computationally efficient than some of the recently published similar works. Being computational efficient, our proposed scheme is feasible on many emergent resource-constrained platforms.