The invention relates to a method of protection, of a Rijndael type algorithm executed by an electronic circuit, against attacks not concealed channels, in which: each block of data to be encrypted or decrypted is masked (31) by a first mask (m) before application (33) of a non-linear block substitution operation from a substitution table (S '), and is unmasked (34) by a second mask (m') after substitution; and the substitution table is recalculated (51, 52, 24), block by block, before application of the nonlinear operation, the processing order of the blocks of the substitution table being subjected to a random permutation (y), commutative with the nonlinear substitution operation.
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