CoChaT Covert Channels in Timed Systems

Serge Haddad was professor at Université Paris-Dauphine when I obtained a position of professor there in september 2004. We did some research work together from this time on, and this cooperation went on after our respective position changes : in Ecole Normale Supérieure de Cachan (feb. 2008) for S. Haddad and in Université Pierre et Marie Curie (sept. 2008) for me. More precisely, a first step of this cooperation, which was joint work with researchers from laboratory IRCCyN in Nantes, was devoted to the study of relations between two classes of timed models which were well known in our respective communities : Time Petri Nets (TPN) and Timed Automata (TA). This led to three communications in international conferences and a journal paper [BCH05c, BCH05a, BCH05b, BCH08]. The first problem concerned the usual semantics of TPN, which did not seem to fit the specification of some classes of timed systems. We proposed two variants for the semantics of TPN and compared their expressive power [BCH05a].We then investigated the comparisons betweenTPNs and TA, from the point of view of language equivalence an bisimulation. While bounded TPNs and TA are language-equivalent, we proved that TA are more powerful when considering bisimulation [BCH05c], and we gave a characterization of the subclass of TA which are bisimilar to a TPN.