Integral Cryptanalysis of Reduced-round KASUMI

Integral cryptanalysis, which was introduced by Knudsen and Wagner, is one of the most powerful attacks on symmetric key ciphers. Attackers preliminarily search integral characteristics of a target cipher for the key-recovery attack. Todo proposed a novel technique named the division property to find them efficiently. In this paper, we apply this technique to the symmetric key block cipher KASUMI which was developed by modifying MISTY1. It has been used worldwide in the 3rd generation mobile communication networks. 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 2
⁶³
data complexity and 2
^63.3
encryptions under the weak key conditions.