METHOD FOR PERFORMING AN ENCRYPTION WITH LOOK-UP TABLES, AND CORRESPONDING ENCRYPTION APPARATUS AND COMPUTER PROGRAM PRODUCT

An encryption method that envisages execution of a encryption algorithm (200) including operations (210) that comprise accessing a look-up table (50), the operation of accessing a look-up table (50) comprising an operation of initialization (100) of the look-up table (50) that comprises writing initialization values in the aforesaid look-up table (50) applying (110; 110, 120) an input mask ( R 1 ) to input data (din, din ref ) that identify a location of said look-up table (50) and an output mask ( R 2 ) to data ( dout, dout ref ) at output from a location of the aforesaid look-up table (50). According to the invention, the above method comprises carrying out at least one second step of initialization (120) of the aforesaid look-up table (50) that comprises: providing at least one second input mask R 1 ¹ and one second output mask R 2 ¹ ; and computing corresponding initialization values as a function of a logic combination (” 1 ) of the aforesaid first input mask ( R 1 ) and second input mask R 1 ¹ and of a logic combination (” 2 ) of the aforesaid first output mask R 2 ¹ and second output mask R 2 º , in such a way that in the resulting table the input data ( din mask ' ) are masked only by the second input mask R 1 ¹ and the output data ( dout mask ' ) are masked only by the second output mask R 2 ¹ .