Abstract
This paper aims at introducing a Petri net semantics of security protocols allowing to study their properties formally. This is obtained by means of an economic but expressive class of composable high-level Petri nets, called S-nets, inspired from works about the relationship between Petri nets and process algebras. S-nets are applied then to give a compositional high-level Petri net semantics to SPL. The Needham-Schr?der protocol is employed to illustrate how this semantics can be used in order to establish the violation of the authentication property.