## Cryptology ePrint Archive: Report 2021/102

A Note on Advanced Encryption Standard with Galois/Counter Mode Algorithm Improvements and S-Box Customization

Madalina Chirita and Alexandru-Mihai Stroie and Andrei-Daniel Safta and Emil Simion

Abstract: Advanced Encryption Standard used with Galois Counter Mode, mode of operation is one of the the most secure modes to use the AES. This paper represents an overview of the AES modes focusing the AES-GCM mode and its particularities. Moreover, after a detailed analysis of the possibility of enhancement for the encryption and authentication phase, a method of generating custom encryption schemes based on GF($2^8$) irreducible polynomials different from the standard polynomial used by the AES-GCM mode is provided. Besides the polynomial customization, the solution proposed in this paper offers the possibility to determine, for each polynomial, the constants that can be used in order to keep all the security properties of the algorithm. Using this customization method, allows changing the encryption schemes over a period of time without interfering with the process, bringing a major improvement from the security point of view by avoiding pattern creation. Furthermore, this paper sets the grounds for implementing authentication enhancement using a similar method to determine the polynomials that can be used instead of the default authentication polynomial, without changing the algorithm strength at all.

Category / Keywords: AES-GCM, Sbox, irreductible polynomials, custom encryption schemes