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.