Revisiting Key-Alternating Feistel Ciphers for Shorter Keys and Multi-user Security

Key-Alternating Feistel (KAF) ciphers, a.k.a. Feistel-2 models, refer to Feistel networks with round functions of the form \(F_i(k_i\oplus x_i)\), where \(k_i\) is the (secret) round-key and \(F_i\) is a public random function. This model roughly captures the structures of many famous Feistel ciphers, and the most prominent instance is DES.