Federated Byzantine Agreement Systems (FBASs) are a fascinating new paradigm
in the context of consensus protocols. Originally proposed for powering the
Stellar payment network, FBASs can instantiate Byzantine quorum systems without
requiring out-of-band agreement on a common set of validators; every node is
free to decide for itself with whom it requires agreement. Sybil-resistant and
yet energy-efficient consensus protocols can therefore be built upon FBASs, and
the “decentrality” possible with the FBAS paradigm might be sufficient to
reduce the use of environmentally unsustainable proof-of-work protocols. In
this paper, we first demonstrate how the robustness of individual FBASs can be
determined, by precisely determining their safety and liveness buffers and
therefore enabling a comparison with threshold-based quorum systems. Using
simulations and example node configuration strategies, we then empirically
investigate the hypothesis that while FBASs can be bootstrapped in a bottom-up
fashion from individual preferences, strategic considerations should
additionally be applied by node operators in order to arrive at FBASs that are
robust and amenable to monitoring. Finally, we investigate the reported
“open-membership” property of FBASs. We observe that an often small group of
nodes is exclusively relevant for determining liveness buffers and prove that
membership in this top tier is conditional on the approval by current top tier
nodes if maintaining safety is a core requirement.
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