Patent Document ID: 20100098242
Application ID: 12253767
Patent Flag: 0

Claim One:
1. A method for evaluating resistance to differential cryptanalysis of a cipher structure having a diffusion element including a linear transformation placed between differently-sized confusion elements at an input of the diffusion element and differently-sized confusion elements at an output of the diffusion element, the method comprising: determining a generalized minimum number N G of non-zero symbols at the input and the output of the diffusion element; dividing the input of the diffusion element into subset inputs S i each having a size corresponding to the size of each confusion element at the diffusion element input; determining, for each subset input, a subset number N Si of non-zero symbols at the subset input and the diffusion element output; summing each subset number to generate a summed subset number SN; subtracting the summed subset number SN from the generalized minimum number N G to generate a worst-case number N W ; calculating an upper bound of a maximum differential characteristic probability P D according to the equation: P D ≤ ( ∏ i = 0 i = n - 1 ( p Si ) N Si ) ( p Sn ) N W where p Si is the maximum differential probability of a confusion element associated with S i , and S n is associated with a confusion element having a lowest resistance against differential attack; and evaluating the resistance to differential cryptanalysis of the cipher structure based on the calculated maximum differential characteristic probability P D .