Meet-in-the-Middle Attacks on 3-Line Generalized Feistel Networks

In the paper, we study the security of 3-line generalized Feistel network, which is a considerate choice for some special needs, such as designing a 96-bit cipher based on a 32-bit round function. We show key recovery attacks on 3line generic balanced Feistel-2 and Feistel-3 based on the meet-in-the-middle technique in the chosen ciphertext scenario. In our attacks, we consider the key size is as large as one-third of the block size. For the first network, we construct a 9-round distinguisher and launch a 10-round key-recovery attack. For the second network, we show a 13-round distinguisher and give a 17-round attack based on some common assumptions.