A Note on the use of the Double Boomerang Connectivity Table (DBCT) for Spotting Impossibilities
Xavier Bonnetain, Virginie Lallemand · HAL (Le Centre pour la Communication Scientifique Directe) · 2024
In this short note we examine one of the impossible boomerang distinguishers of Skinny-128-384 provided by Zhang, Wang and Tang at ToSC 2024 Issue 2 and disprove it. The issue arises from the use of the Double Boomerang Connectivity Table (DBCT) as a tool to establish that a boomerang switch over 2 rounds has probability zero, whereas the DBCT only covers specific cases of difference propagation, missing a large set of events that might make the connection possible. We study in details the specific instance provided by Zhang et al. and display one example of a returning quartet that contradicts the impossibility.