Revisit and Cryptanalysis of a CAST Cipher

Abstract

CAST family of ciphers are the block ciphers created by Carlisle Adams et al. in 1996. One famous member of CAST family is CAST-128, which is a 12-round or 16-round Feistel network. In this paper, we apply the interpolation attack on both 5- round and 16-round CAST-128 Cipher to recover the last round key. We first mount the basic interpolation attack separately on it. After combining with the higher order differential cryptanalysis, our result reduces the time complexity in 231.4 bit operation for 5-round attack. We also apply the optimized interpolation attack on the 16-round CAST-128-like structure which requires 244.2 bit operations and 231 chosen plaintexts.