  We delineate a methodology for the specification and verification of flow
security properties expressible in the opacity framework. We propose a logic,
OpacTL , for straightforwardly expressing such properties in systems that can
be modelled as partially observable labelled transition systems.We develop
verification techniques for analysing property opacity with respect to
observation notions. Adding a probabilistic operator to the specification
language enables quantitative analysis and verification. This analysis is
implemented as an extension to the PRISM model checker and illustrated via a
number of examples. Finally, an alternative approach to quantifying the opacity
property based on entropy is sketched.
