METHOD TO SECURE KECCAK ALGORITHM AGAINST SIDE-CHANNEL ATTACKS

The present invention relates to a method to secure a cryptographic algorithm (F) performing operations on a matrix of n*n words (A), this cryptographic algorithm (F) necessitating to, when the matrix of data (A) is masked using a mask matrix (M), performing operations on the masked matrix (A+M) and on a mask matrix (M), said method comprising the steps of generating (GEN) a maximum of n*(n-1) random values (RV) of the size of the words of the matrix (A) for the masking of the data, constructing (MCM) a mask matrix (M) where at least n values are obtained by an combination of at least two of the generated random values (RV). Recovery of masked intermediate matrix (F(A)+M) comprising a step of constructing (DCM) a set of degraded operations (F') to be applied on values in mask matrix (M) instead of the whole set of operations of the algorithm (F) to be applied on the whole mask matrix (F(M)).