Meet‐in‐the‐middle attacks on round‐reduced tweakable block cipher Deoxys‐BC

Abstract

Deoxys-BC is a tweakable block cipher designed by Jean et al. at ASIACRYPT 2014 within the TWEAKEY framework. Then Deoxys-BC is used in the CAESAR finalist Deoxys. In this study, the authors consider the security of Deoxys-BC against meet-in-the-middle attack in the single-key setting. Using the idea that a chosen tweak difference allows to cancel a difference in the state, they can construct 5-round meet-in-the-middle distinguisher on Deoxys-BC-128-128 which can be extended to attack on 8-round Deoxys-BC-128-128. Moreover, they construct 6-round meet-in-the-middle distinguisher on Deoxys-BC-256-128 which can be extended to attack on 10-round Deoxys-BC-256-128. As far as the authors know, these are the best attacks against Deoxys-BC in the single-key setting.