Generalization of Matsui's Algorithm 1 to linear hull for key-alternating block ciphers

  • Authors:
  • Andrea Röck;Kaisa Nyberg

  • Affiliations:
  • Department of Information and Computer Science, Aalto University School of Science, Aalto, Finland 00076;Department of Information and Computer Science, Aalto University School of Science, Aalto, Finland 00076 and Nokia Research Center, Nokia Group, Finland 00045

  • Venue:
  • Designs, Codes and Cryptography
  • Year:
  • 2013

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Abstract

We consider linear approximations of an iterated block cipher in the presence of several strong linear approximation trails. While the effect of such trails in Matsui's Algorithm 2, also called the linear hull effect, has been previously studied by a number of authors, their effect on Matsui's Algorithm 1 has not been investigated until now. The goal of this paper is to fill this gap and examine how to generalize Matsui's Algorithm 1 to work also on linear hulls. We restrict to key-alternating ciphers and develop a mathematical framework for this kind of attacks. The complexity of the attack increases with the number of linear trails that have significant contribution to the correlation. We show how to reduce the number of trails and thus the complexity using related keys. Further, we illustrate our theory by experimental results on a reduced round version of the block cipher PRESENT.