A method of verifying the sensitivity of an electronic circuit executing a Rijndael-type algorithm to side channel attacks, wherein: each block of data to be encrypted or to be decrypted is masked with a first mask before a non-linear block substitution operation is applied based on a substitution box, and is then unmasked with a second mask after the substitution; the substitution box is recalculated, block by block, before the non-linear operation is applied, the processing order of the blocks of the substitution box being submitted to a permutation; and a side channel attack is performed on the steps of recalculating, block by block, the substitution box.