Guo, Jian, Jérémy Jean, Ivica Nikolic, and Yu Sasaki. “Meet-in-the-Middle Attacks on Classes of Contracting and Expanding Feistel Constructions”. IACR Transactions on Symmetric Cryptology 2016, no. 2 (February 3, 2017): 307-337. Accessed April 6, 2020. https://tosc.iacr.org/index.php/ToSC/article/view/576.