The analysis of a new class of unbalanced CAST ciphers

The original CAST cipher is an efficient and secure private key block cipher designed to be an alternative to DES. We present a new class of unbalanced CAST ciphers which employ the same structure of S box and round function as the original CAST cipher but has a lower memory requirement. Furthermore, we investigate the security of the ciphers with respect to differential and linear cryptanalysis. The result of analysis shows that unbalanced CAST ciphers with appropriate parameters are resistant to differential and linear cryptanalysis.