Building Byzantine-tolerant Systems with Distributed Ledgers and Distributed Sets

Abstract

In order to formalize Distributed Ledger Technologies and their interconnections, a recent line of research work has formulated the notion of Distributed Ledger Object (DLO), which is a concurrent object that maintains a totally ordered sequence of records, abstracting blockchains and distributed ledgers. It has been shown that solving consensus is required to implement a multi-writer DLO. However, it is possible to implement Byzantine-tolerant atomic single-writer DLOs without consensus in a distributed system of n servers, of which f<n/3 can be Byzantine. In the same line, the Distributed Grow-only Set object (DSO) has been proposed, which maintains a set (instead of a sequence) of records in an immutable way: only Add and Get operations are provided. This object is inspired by the Grow-only Set (G-Set) data type which is part of the Conflict-free Replicated Data Types. There are consensus-free Byzantine-tolerant implementations of the DSO that guarantee eventual consistency. Fundamental coordination challenges in these objects are the Atomic Appends and Atomic Adds problems, by which multiple records are added to distinct DLOs or DSOs in an atomic way. In this talk we introduce these objects and problems, and we describe how they can be implemented and solved in Byzantine distributed systems.