Improved related‐tweakey rectangle attacks on round‐reduced Deoxys‐BC

Deoxys-BC is the internal tweakable block cipher of authenticated encryption (AE) Deoxys family, in which Deoxys-II primary choice for use case ‘Defence depth’ among portfolio CAESAR competition. Improvements related-tweakey rectangle attacks on round-reduced using known distinguishers focussed this study. Under new related-key attack framework proposed by Dong et al. EUROCRYPT 2022, we present three kinds precomputed tables to further reduce time complexity key-recovery phase. In attack, invalid quartets are filtered or subtweakey candidates obtained lookup without more computation. Based table technique, improved 11-round Deoxys-BC-256, 13-round and 14-round Deoxys-BC-384. Furthermore, AE scheme Deoxys-I-256-128 a factor 224 compared with best previous attack.