Improved Impossible Differential Attack on 7-round Reduced ARIA-256

Abstract

ARIA is an involutory SPN block cipher. Its block size is 128-bit and the master key sizes are 128/192/256-bit, respectively. Accordingly, they are called ARIA-128/192/256. As we all know, ARIA is a Korean Standard block cipher nowadays. This paper focuses on the security of ARIA against impossible differential attack. We firstly construct a new 4-round impossible differential of ARIA. Furthermore, based on this impossible differential, a new 7-round impossible differential attack on ARIA-256 is proposed in our paper. This attack needs 2 118 chosen plaintexts and 2 210 7-round encryptions. Comparing with the previous best result, we improve both the data complexity and time complexity. To our knowledge, it is the best impossible differential attack on ARIA-256 so far.