On the security of the IDEA block cipher

Abstract

IDEA is an iterated block cipher proposed by Lai and Massey and is based on the design concept of “Mixing operations from Merent algebraic groups”. New arithmetic properties of the basic operations used in the round function are found and investigated with respect to the security of this block cipher. Evidence is given that these properties can be exploited in the cryptanalysis of the fist 2 rounds of IDEA but that they are of no asubtancc in the cryptanalyais of the full IDEA block cipher containing 8 rounds.