A cryptographic circuit performs a substitution operation of a cryptographic algorithm based on a scrambled substitution table. For each set of one or more substitution operations of the cryptographic algorithm, the circuit performs a series of sets of one or more substitution operations of which: one is a real set of one or more substitution operations defined by the cryptographic algorithm, the real set of one or more substitution operations being based on input data modified by a real scrambling key; and one or more others are dummy sets of one or more substitution operations, each dummy set of one or more dummy substitution operations being based on input data modified by a different false scrambling key.