An encryption method includes accessing a look-up table (LUT) to implement countermeasures against side-channel attacks, such as embedding masks. The LUT is initialized by writing initialization values in the LUT by applying an address-mask to input data that identify a location of said LUT and a data-mask to data to be stored at a location of the LUT. The method includes carrying out an initialization of the LUT that includes providing at least one second address-mask and one second data-mask; and computing corresponding initialization values as a function of a logic combination of the aforesaid first address-mask and second address-mask and of a logic combination of the aforesaid first data-mask and second data-mask. In the resulting table the address data are masked only by the second address-mask and the data are masked only by the second data-mask. The structure of the LUT may allow convenient implementation by initializing all the values of the LUT in parallel in one cycle.