Dynamically Choosing S-Boxes Using SHA-256

Cloud storage as a service has transformed the way organizations handle data in the past few years. Its main advantages are reduced cost, increased flexibility, scalability, and availability. However, cloud storage is paired with security threats since the service provider can access the users' data. Therefore, storing data in the cloud is a concern in the military, medical, and social sectors. Thus, we present a 3-layer image cryptosystem that allows users to benefit from cloud storage without compromising data security. Each layer had a key created using the single neuron approach and an S-box selected based on a passkey that had been SHA-256 encrypted. Histogram analysis, MSE, PSNR calculations, entropy values, and pixel co-occurrence matrices validate the proposed approach. The proposed color image cryptosystem successfully passes the PRNG suitability tests outlined in NIST SP-800 STS. The average encryption rate is 5.81543 Mbps using Windows 10 PC with an Intel Core i7-9750H CPU @ 2.6 GHz and 16 GB of memory, as well as Wolfram Mathematica 13.1.