@article{Boukerrou_Huynh_Lallemand_Mandal_Minier_2020, title={On the Feistel Counterpart of the Boomerang Connectivity Table: Introduction and Analysis of the FBCT}, volume={2020}, url={https://tosc.iacr.org/index.php/ToSC/article/view/8568}, DOI={10.13154/tosc.v2020.i1.331-362}, abstractNote={<p>At Eurocrypt 2018, Cid et al. introduced the Boomerang Connectivity Table (BCT), a tool to compute the probability of the middle round of a boomerang distinguisher from the description of the cipher’s Sbox(es). Their new table and the following works led to a refined understanding of boomerangs, and resulted in a series of improved attacks. Still, these works only addressed the case of Substitution Permutation Networks, and completely left out the case of ciphers following a Feistel construction. In this article, we address this lack by introducing the FBCT, the Feistel counterpart of the BCT. We show that the coefficient at row Δ<sub><em>i</em></sub>, ∇<sub><em>o</em></sub> corresponds to the number of times the second order derivative at points Δ<sub><em>i</em></sub>, ∇<sub><em>o</em></sub>) cancels out. We explore the properties of the FBCT and compare it to what is known on the BCT. Taking matters further, we show how to compute the probability of a boomerang switch over multiple rounds with a generic formula.</p>}, number={1}, journal={IACR Transactions on Symmetric Cryptology}, author={Boukerrou, Hamid and Huynh, Paul and Lallemand, Virginie and Mandal, Bimal and Minier, Marine}, year={2020}, month={May}, pages={331-362} }