  The federated Byzantine agreement system (FBAS) is a consensus model
introduced by Mazi\`eres in 2016 where the participating nodes conceptually
form a network, with links between them being established by each node
individually and thus in a decentralized way. An important question is whether
these decentralized decisions lead to an overall decentralized network. The
level of (de-)centralization in a network can be assessed using centrality
measures. In this paper we consider three different approaches for obtaining
centrality measures for the nodes in an FBAS. Two of them are based on adapting
well-known measures based on graphs and hypergraphs to the FBAS context. Since
the network structure of an FBAS can be more complex than (usual) graphs or
hypergraphs, we also develop a new, problem-adapted centrality measure. This
new measure is based on the intactness of nodes, which is an important
ingredient of the FBAS model. We illustrate advantages and disadvantages of the
three approaches on several computed examples. We have implemented all
centrality measures and performed all computations in the Python package
Stellar Observatory.

Distributed, Parallel, and Cluster Computing