HIDING OF A PROGRAM EXECUTION

A system for hiding a change to a set of variables of a program is provided. A value representing means (902) represents a value w i of a variable v i of the variables v 1, v 2,..., v n, wherein w is an element of a set W, by means of a representation r i wherein r i = E(Wi, σ i ), and r i is an element of a set of representations Ω(w i ) = {Ε(νν ί ,s) |s ∈∑}, wherein σ i is a state variable that is an element of a set ∑ and that provides a redundancy to the representation r i of w i and E is a one-to-one cryptographic mapping from W x∑ to a predetermined set. An action representing means (903) represents an action on values of variables in a subset V' of V by means of an action on V' and an action on V \V', to obtain updated representations. The action on V' changes the representation r j of each variable V j in the set of variables.