Patent ID: 7386130

Claim:
An encryption device comprising XOR means and nonlinear transform means, said encryption device further comprising: a random number generator for generating a random number h, where h is an integer between zero and q−1; q sets of fixed mask values FM i,h , where q is an integer equal to three or more, wherein equations, FM 0,h =C h XOR L 1 0 (FMin h ), and C h =c h,15 c h,14 . . . c h,0 , are satisfied, where FM i,h is the i-th fixed value of the h-th set of said q sets of fixed mask values, where FMin h is a selected one of said fixed mask values, and where i is an integer, q sets of fixed S-box table, wherein equations, (c 0,j XOR c 1,j ) v (c 1,j XOR c 2,j ) v . . . v (c q−2,j XOR c q−1,j )=(111 . . . 11) 2 and (d 0,j XOR d 1,j ) v (d 1,j XOR d 2,j ) v . . . v (d q−2,j XOR d q−1,j )=(111 . . . 11) 2 are satisfied, a fixed S-box table before masking is defined as S[x], and i-th masked fixed S-box table is defined as S j,h [x]=[x XOR c h,j ] XOR d hj for the j-th fixed value, where j is an integer; linear transform means L 1 i (x) and linear transform means L 2 i (x), wherein the linear transform means L 1 i (x), the nonlinear transform means with the masked fixed S-box table S j,h [x] and the linear transform means L 2 i (x) operate in i-th one of rounds; and a first selector for selecting one fixed value of the h-th set of said q sets of fixed mask values in response to the random number h, said XOR means XORing an input thereto with an XOR of a key with said selected fixed value.