Cryptographic Weaknesses in the Round Transformation Used in a Block Cipher with Provable Immunity Against Linear Cryptanalysis (Extended Abstract)

MISTY is a data encryption algorithm recently proposed by M Matsui from Mitsubishi Electric Corporation This paper focuses on cryptographic roles of the transform used in the MISTY cipher Our research reveals that when used for constructing pseudorandom permu tations the transform employed by the MISTY cipher is inferior to the transform in DES though the former is superior to the latter in terms of strength against linear and di erential attacks More speci cally we show that a round round respectively concatenation of transforms used in the MISTY cipher is not a pseudorandom super pseudorandom respectively permutation For comparison we note that with three four respectively rounds transforms used in DES yield a pseudorandom su per pseudorandom respectively permutation Another contribution of this paper is to show that a round concate nation of transforms used in the preliminary version of the MISTY cipher has an algebraic property which may open a door for various cryptanalytic attacks