Integral Cryptanalysis on Reduced-round KASUMI

抄録

Integral cryptanalysis is one of the most powerful attacks on symmetric key block ciphers. Attackers preliminarily search integral characteristics of a target cipher and use them for an attack. Todo proposed a novel technique named the bit-based division property to find integral characteristics. Xiang et al. extended Mixed Integer Linear Programming (MILP) method to search integral characteristics of lightweight block ciphers based on the bit-based division property. In this paper, we apply these techniques to the symmetric key block cipher KASUMI which was developed by modifying MISTY1. As a result, we found new 4.5-round characteristics of KASUMI for the first time. We show that 7-round KASUMI is attackable with 2⁶³ data and 2¹²⁰ encryptions.