Improved State-Recovery Attacks on Modified KETJE JR

Abstract

KETJE, a lightweight authenticated encryption cipher is a third-round candidate of CAESAR competition whose design principles are similar to SHA-3 hash function. Fuhr et al. studied the security of KETJE JR against divide-and-conquer attacks and proposed state-recovery attacks on modified KETJE JR. In this paper, we study the relations among the algebraic representations of internal state bits, and find new guessing strategies based on Fuhr et al.'s method. With the usage of new guessing strategies, we improve the state-recovery attacks on KETJE JR v1 when r=40 and r=32. Compared with Fuhr et al.'s work, our results are more efficient. The relults do not threaten the security of KETJE in practice, but provide evidence for improving the efficiency of KETJE by increasing the rate.