A complete formulation of generalized affine equivalence

  • Authors:
  • Marco Macchetti;Mario Caironi;Luca Breveglieri;Alessandra Cherubini

  • Affiliations:
  • Politecnico di Milano, Milan, Italy;Politecnico di Milano, Milan, Italy;Politecnico di Milano, Milan, Italy;Politecnico di Milano, Milan, Italy

  • Venue:
  • ICTCS'05 Proceedings of the 9th Italian conference on Theoretical Computer Science
  • Year:
  • 2005

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Abstract

In this paper we present an extension of the generalized linear equivalence relation, proposed in [7]. This mathematical tool can be helpful for the classification of non-linear functions f : Fpm→ Fpnbased on their cryptographic properties. It thus can have relevance in the design criteria for substitution boxes (S-boxes), the latter being commonly used to achieve non-linearity in most symmetric key algorithms. First, we introduce a simple but effective representation of the cryptographic properties of S-box functions when the characteristic of the underlying finite field is odd; following this line, we adapt the linear cryptanalysis technique, providing a generalization of Matsui’s lemma. This is done in order to complete the proof of Theorem 2 in [7], also by considering the broader class of generalized affine transformations. We believe that the present work can be a step towards the extension of known cryptanalytic techniques and concepts to finite fields with odd characteristic.