The Analysis of a New Class of Unbalanced CAST Ciphers

a New Class of Unbalanced CAST Ciphers X. Zhu and H. M. Heys Faculty of Engineering and Applied Science Memorial University of Newfoundland St. John's, Newfoundland, Canada, A1B 3X5 Email: [email protected] Abstract The original CAST cipher is an e cient and secure private-key block cipher designed to be an alternative to DES. In this paper, 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 di erential and linear cryptanalysis. The result of analysis shows that unbalanced CAST ciphers with appropriate parameters are resistant to di erential and linear cryptanalysis.