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Erschienen in:
2016 | OriginalPaper | Buchkapitel
A \(2^{70}\) Attack on the Full MISTY1
verfasst von : Achiya Bar-On, Nathan Keller
Erschienen in: Advances in Cryptology – CRYPTO 2016
Verlag: Springer Berlin Heidelberg
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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.