  Intruders can infer properties of a system by measuring the time it takes for
the system to respond to some request of a given protocol, that is, by
exploiting time side channels. These properties may help intruders distinguish
whether a system is a honeypot or concrete system helping him avoid defense
mechanisms, or track a user among others violating his privacy. Observational
equivalence is the technical machinery used for verifying whether two systems
are distinguishable. Moreover, efficient symbolic methods have been developed
for automating the check of observational equivalence of systems. This paper
introduces a novel definition of timed observational equivalence which also
distinguishes systems according to their time side channels. Moreover, as our
definition uses symbolic time constraints, it can be automated by using
SMT-solvers.
