Compositional weak metrics for group key update

We investigate the compositionality of both weak bisimilarity metric and weak similarity quasimetric semantics with respect to a variety of standard operators, in the context of probabilistic process algebra. We show how compositionality with respect to nondeterministic and probabilistic choice requires to resort to rooted semantics. As a main application, we demonstrate how our results can be successfully used to conduct compositional reasonings to estimate the performances of group key update protocols in a multicast setting.