Improved meet‐in‐the‐middle attacks on reduced‐round Joltik‐BC

Abstract

Joltik-BC is an internal tweakable block cipher of the authenticated encryption algorithm Joltik, which was a second-round finalist in the CAESAR competition. The authors study the key-recovery attacks on Joltik-BC under meet-in-the-middle attack. Utilising the subtweakey difference cancellation, the freedom of the tweak and the differential enumeration, they attack on nine-round Joltik-BC-64-64 by constructing a precise six-round meet-in-the-middle distinguisher with 253 plaintext–tweak combinations, 252.91 Joltik-BC blocks and 254.1 nine-round Joltik-BC-64-64 encryptions. Moreover, they attempt to attack on 11-round Joltik-BC-128-64 for the first time by constructing a seven-round meet-in-the-middle distinguisher with 253 plaintext–tweak combinations, 2114 Joltik-BC blocks and 2123 11-round Joltik-BC-128-64 encryptions.