an:06861494
Zbl 1384.93137
B??rard, B??atrice; Kouchnarenko, Olga; Mullins, John; Sassolas, Mathieu
Opacity for linear constraint Markov chains
EN
Discrete Event Dyn. Syst. 28, No. 1, 83-108 (2018).
00376589
2018
j
93E03 60H10 93C05
opacity; Markov models; specification; refinement
Summary: On a partially observed system, a secret \(\varphi\) is opaque if an observer cannot ascertain that its trace belongs to \(\varphi\). We consider specifications given as Constraint Markov Chains (CMC), which are underspecified Markov chains where probabilities on edges are required to belong to some set. The nondeterminism is resolved by a scheduler, and opacity on this model is defined as a worst case measure over all implementations obtained by scheduling. This measures the information obtained by a passive observer when the system is controlled by the smartest scheduler in coalition with the observer. When restricting to the subclass of linear CMC, we compute (or approximate) this measure and prove that refinement of a specification can only improve opacity.