Differential cryptanalysis of blow-CAST-fish

Abstract

Blow-CAST-Fish is a sixteen-round Feistel cipher in which the F function is a part of the private key. In this paper, we show that the disclosure of F allows perform a differential cryptanalysis against a number of rounds. We firstly identify the properties of F function with three active S-boxes to construct the 6-round differential characteristic with the probability 2 -61 and the differential weak keys occur with the probability 2 -12. Then we identify the properties of F function with only one active S-box to construct the 14-round differential characteristic with the probability 2-49 and the differential weak keys occur with the probability 2-52. With the above differential characteristics, we can attack 8-round and 16-round Blow-CAST-Fish respectively. © Springer Science+Business Media B.V. 2010.