A test method can include: acquiring a plurality of value sets including measurements or signals corresponding with activity of a circuit when executing a set of cryptographic operations on secret data, for each value set, selecting at least two subsets of values, computing combined values and counting occurrence numbers of values transformed by a first surjective function applied to the combined values, for each operation and each possible value of a part of the secret data, computing a partial operation result, computing cumulative occurrence number sets by adding the occurrence number sets corresponding to the operations of the operation set, which when applied to a same value of the possible values of the part of the secret data, provide a partial operation result having a same transformed value by a second surjective function, and determine the part of the secret data from the cumulative occurrence number sets.