Differential forgery attack against LAC

Abstract

LAC is one of the candidates to the CAESAR competition. In this paper we present a differential forgery attack on LAC. We study the collection of characteristics following a fixed truncated characteristic, in order to obtain a lower bound on the probability of a differential. We show that some differentials have a probability higher than 2 −64, which allows a forgery attack on the full LAC. This work illustrates the difference between the probability of differentials and characteristics, and we describe tools to evaluate the probability of some characteristics.