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A \(2^{70}\) Attack on the Full MISTY1

  • Achiya Bar-OnEmail author
  • Nathan Keller
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 9814)

Abstract

MISTY1 is a block cipher designed by Matsui in 1997. It is widely deployed in Japan, and is recognized internationally as a European NESSIE-recommended cipher and an ISO standard. After almost 20 years of unsuccessful cryptanalytic attempts, a first attack on the full MISTY1 was presented at CRYPTO 2015 by Yosuke Todo. The attack, using a new technique called division property, requires almost the full codebook and has time complexity of \(2^{107.3}\) encryptions.

In this paper we present a new attack on the full MISTY1. It is based on Todo’s division property, along with a variety of refined key-recovery techniques. Our attack requires almost the full codebook (like Todo’s attack), but allows to retrieve 49 bits of the secret key in time complexity of only \(2^{64}\) encryptions, and the full key in time complexity of \(2^{69.5}\) encryptions.

While our attack is clearly impractical due to its large data complexity, it shows that MISTY1 provides security of only \(2^{70}\) — significantly less than what was considered before.

Keywords

Time Complexity Block Cipher Affine Subspace Encryption Direction Linear Cryptanalysis 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© International Association for Cryptologic Research 2016

Authors and Affiliations

  1. 1.Department of MathematicsBar Ilan UniversityRamat GanIsrael

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