Further Security Evaluation for a Class of Generalized Feistel Ciphers

To evaluate the security of a class of generalized Feistel cipher s, the security evaluation against differential and linear cryptanalyses is investigated deeply using iterative structure. If round functions are all bijective, then the number of active round functions for 4-r round(r\1) ciphers are not less than(8/ 3) r-[(rmod3)/3] +(rmod3)/3. The result is at least improved20% than the existing result when r\6. So the upper bounds of maximum differential characteristic and linear approximation probabilities for 4-r round(r\1) ciphers can be estimated if maximum differential and linear approximation probabilities for round function are given.