  Quantitative information flow analyses measure how much information on
secrets is leaked by publicly observable outputs. One area of interest is to
quantify and estimate the information leakage of composed systems. Prior work
has focused on running disjoint component systems in parallel and reasoning
about the leakage compositionally, but has not explored how the component
systems are run in parallel or how the leakage of composed systems can be
minimised. In this paper we consider the manner in which parallel systems can
be combined or scheduled. This considers the effects of scheduling channels
where resources may be shared, or whether the outputs may be incrementally
observed. We also generalise the attacker's capability, of observing outputs of
the system, to consider attackers who may be imperfect in their observations,
e.g. when outputs may be confused with one another, or when assessing the time
taken for an output to appear. Our main contribution is to present how
scheduling and observation effect information leakage properties. In
particular, that scheduling can hide some leaked information from perfect
observers, while some scheduling may reveal secret information that is hidden
to imperfect observers. In addition we present an algorithm to construct a
scheduler that minimises the min-entropy leakage and min-capacity in the
presence of any observer.
