On the Role of Scheduling in Simulation-Based Security

In a series of papers, Küsters et al. investigated the relationships between various notions of simulation-based security. Two main factors, the placement of a “master process” and the existence of “forwarder processes”, were found to affect the relationship between different definitions. In this extended abstract, we add a new dimension to the analysis of simulation-based security, namely, the scheduling of concurrent processes. We show that, when we move from sequential scheduling (as used in previous studies) to task-based nondeterministic scheduling, the same syntactic definition of security gives rise to incomparable semantic notions of security. Under task-based scheduling, the hierarchy based on placement of “master process” is no longer relevant, because no such designation is necessary to obtain meaningful runs of a system. On the other hand, the existence of “forwarder processes” remains an important factor.