A cryptography circuit protected by masking, said circuit including means for encrypting binary words using at least one key krc, means for applying linear processing operations and nonlinear processing operations to said words and means for masking said words. The binary words are unmasked upstream of the nonlinear processing operations by using a mask kri and masked downstream of said processing operations by using a mask kr+1i, the masks kri and kr+1i being chosen from a set of masks that is specific to each instance of the circuit.