A method of detecting a fault attack during a cryptographic operation using at least one look-up table including a plurality of sub-tables each having a same number of values of a fixed bit length, a fixed relation existing between values at same locations in each sub-table, the method including: performing a load operation to retrieve from the look-up table data values from a same location in each sub-table; verifying that the fixed relation exists between at least two of the data values; and generating an output signal based on the verification.