Pon. Partheeban, N. Nityanandam
Generation of Dynamic S-Box Using Irreduceable Polynomial and the Secret Key Used
Advanced Encryption Standard (AES) is one of the best cryptographic algorithms that can be used to protect electronic data. Its security has attracted cryptographist’s attentions. The result of new attack methods shows that there may be some lacuna in the design of S-box and key schedule with AES algorithm. The principal weakness in the AES algorithm is the problem of linearity in the S-box. In order to keep away from the new attacks and implement the AES for secure communication, a detailed analysis on the design of S-box is carried out and a new implementation scheme for increasing the complexity of S-box is designed by applying nonlinear transformations. For each composite field constructions, there exist eight possible isomorphic mappings. After the exploitation of a new common sub-expression elimination algorithm, the isomorphic mapping that results in the minimal implementation cost is chosen. S-box is the only component to implement nonlinear transformation in AES. The cryptographic strength of the AES depends strongly on the choice of Sbox. The S-box used in the traditional AES has the properties of short periods and bad distribution. In order to make up the weakness of the existing S-box we generate a dynamic S-box that is dependent on the key. Discrete logarithmic approach is used to improve non-linearity of the S-box. Also, Walsh Hadamard transform matrix is used to decide on the strength of the key and to find the most non-linear key.
