Rotational Cryptanalysis in the Presence of Constants

  • Tomer Ashur Dept. Electrical Engineering (ESAT), KU Leuven and iMinds, Leuven
  • Yunwen Liu Dept. Electrical Engineering (ESAT), KU Leuven and iMinds, Leuven; College of Science, National University of Defense Technology, Changsha
Keywords: Rotational cryptanalysis, ARX, RX-difference

Abstract

Rotational cryptanalysis is a statistical method for attacking ARX constructions. It was previously shown that ARX-C, i.e., ARX with the injection of constants can be used to implement any function. In this paper we investigate how rotational cryptanalysis is affected when constants are injected into the state. We introduce the notion of an RX-difference, generalizing the idea of a rotational difference. We show how RX-differences behave around modular addition, and give a formula to calculate their transition probability. We experimentally verify the formula using Speck32/64, and present a 7-round distinguisher based on RX-differences. We then discuss two types of constants: round constants, and constants which are the result of using a fixed key, and provide recommendations to designers for optimal choice of parameters.

Published
2016-12-01
How to Cite
Ashur, T., & Liu, Y. (2016). Rotational Cryptanalysis in the Presence of Constants. IACR Transactions on Symmetric Cryptology, 2016(1), 57-70. https://doi.org/10.13154/tosc.v2016.i1.57-70
Section
Articles