  In contrast to proof-of-work replication, Byzantine replicated systems
maintain consistency with higher throughput, modest energy consumption, and
deterministic liveness guarantees. If complemented with open membership and
heterogeneous trust, they have the potential to serve as a global financial
infrastructure. This paper presents a general model of heterogeneous quorum
systems, where each participant can declare its own quorums, and captures the
consistency, availability, and inclusion properties of these systems. In order
to support open membership, it then presents reconfiguration protocols for
heterogeneous quorum systems: joining and leaving of a process, and adding and
removing of a quorum. It presents trade-offs for the properties that
reconfigurations can preserve, and accordingly, presents reconfiguration
protocols and proves their correctness. It further presents a graph
characterization of heterogeneous quorum systems, and its application for
reconfiguration optimization.
