Construction of Key-dependent S-box for Secure Cloud Storage

As cloud storage systems have developed and been applied in complex environments, their data security has become more prevalent in recent years. The issue has been approached through many models. Data is encrypted and stored in these models. One of the most widely used encryption methods is the Advanced Encryption Standard (AES). In AES, the Substitution box(S-box) is playing a significant part in imparting the job of confusion. The security of the entire cryptosystem depends on its nonlinearity. In this work, a robust and secure S-box is constructed using a novel method, i.e., fingerprint features-based permutation function. Two stages are considered to construct a strong S-box. Firstly, random numbers are generated from the fingerprint features such as bifurcation and ridge endings of the user transmitting data. Subsequently, the permutation function is adapted on the random numbers (developed in the first stage) to augment the strength of the S-box. National Institute of Standards and Technology (NIST) STS 800-22 test suite is considered to evaluate the randomness of the enhanced fingerprint-based S-box. Also, the robustness of the constructed S-box is tested using cryptographical properties, namely Strict Avalanche Criterion (SAC), Nonlinearity (NL), Differential Approximation (DA) probability and output Bits Independence Criterion (BIC). Later, the cryptographical properties of the proposed S-box are compared with several existing S-boxes. After analyzing the characteristics of the proposed scheme, it is revealed that the newly constructed S-box is powerful, robust, and safe against linear and differential assaults.