Title: Study of randomness in AES ciphertexts produced by various types of dynamic S-boxes

Authors: S. Das; Ranjan Ghosh

Addresses: Department of Computer Science and Engineering, University of Calcutta, 92 APC Road, Kolkata, India ' Department of Computer Science and Engineering, University of Calcutta, 92 APC Road, Kolkata, India

Abstract: In this paper, it has been shown that besides using the standard one, many other polynomials in GF(28) can be used as the modulus to generate a secured AES S-box by modular arithmetic. The same is true for additive constants in GF(2) also. It has also been shown that secured AES S-boxes can also be generated by a suitable PRNG, such as BBS. These new types of S-boxes are all user-defined, i.e., unknown S-boxes, and so they are able to prevent linear and differential cryptanalysis. Using these S-boxes, a comparative study on the corresponding AES ciphertexts has been made by using the NIST test suite coded by the authors. It has been observed that besides the standard ones, other moduli and additive constants are also able to generate equally or better random ciphertexts; the same is true for PRNG driven random S-boxes also. Moreover, these parameters can be used as additional key-inputs to AES, thus increasing the key-space.

Keywords: Advanced Encryption Standard; block cipher; AES S-boxes; random S-boxes; NIST test suite; BBS S-box; AES secondary key; randomness; AES ciphertexts; S-boxes.

DOI: 10.1504/IJICT.2015.072037

International Journal of Information and Communication Technology, 2015 Vol.7 No.6, pp.537 - 561

Received: 02 Sep 2013
Accepted: 06 Jan 2014

Published online: 03 Aug 2015 *

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