  With the advent of digital communication, securing digital images during
transmission and storage has become a critical concern. The traditional s-box
substitution methods often fail to effectively conceal the information within
highly auto-correlated regions of an image. This paper addresses the security
issues presented by three prevalent S-box substitution methods, i.e., single
S-box, multiple S-boxes, and multiple rounds with multiple S-boxes, especially
when handling images with highly auto-correlated pixels. To resolve the
addressed security issues, this paper proposes a new scheme SRSS-the Single
Round Single S-Box encryption scheme. SRSS uses a single S-box for substitution
in just one round to break the pixel correlations and encrypt the plaintext
image effectively. Additionally, this paper introduces a new Chaos-based Random
Operation Selection System-CROSS, which nullifies the requirement for multiple
S-boxes, thus reducing the encryption scheme's complexity. By randomly
selecting the operation to be performed on each pixel, driven by a chaotic
sequence, the proposed scheme effectively scrambles even high auto-correlation
areas. When compared to the substitution methods mentioned above, the proposed
encryption scheme exhibited exceptionally well in just a single round with a
single S-box. The close-to-ideal statistical security analysis results, i.e.,
an entropy of 7.89 and a correlation coefficient of 0.007, validate the
effectiveness of the proposed scheme. This research offers an innovative path
forward for securing images in applications requiring low computational
complexity and fast encryption and decryption speeds.
