1. Secure data processing method, characterized in that it comprises the following steps: filling (E 206 ; E 510 ; E 804 ) an area (MAC′; BUF) of memory with a filling value (A; A 1 ; A); writing (E 208 ; E 512 ; E 806 ) a first data item in this area (MAC′; BUF); reading (E 210 ; E 514 ; E 808 ) in this area a second data item repeating at least a portion of the first data item as written in this area (MAC′; BUF); executing (E 210 ; E 514 ; E 808 ) an operation using the second data item.