M. Naor (Ed.): TCC 2004, LCNS 2951, pages 336 352, February 2004. c © Springer-Verlag Berlin Heidelberg 2004. Abstract. We consider compositional properties of reactive systems that are secure in a cryptographic sense. We follow the well-known simulatability approach of modern cryptography, i.e., the specification is an ideal system and a real system should in some sense simulate this ideal one...