Byzantine-tolerant Distributed Grow-only Sets: Specification and Applications

TL;DR

This paper introduces a Byzantine-tolerant distributed grow-only set (BDSO) that maintains an immutable set of records, providing consensus-free solutions for atomic appends and related problems in distributed ledger systems.

Contribution

It formally specifies a Byzantine-tolerant grow-only set object and offers the first consensus-free implementation with practical applications in distributed ledgers.

Findings

Provides a formal specification of BDSO.

Offers a consensus-free Byzantine-tolerant implementation.

Enables atomic appends and adds without consensus.

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. Through DLO, the Atomic Appends problem, intended as the need of a primitive able to append multiple records to distinct ledgers in an atomic way, is studied as a basic interconnection problem among ledgers. In this work, we propose the Distributed Grow-only Set object (DSO), which instead of maintaining a sequence of records, as in a DLO, maintains a set 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. We formally specify the object and we provide a consensus-free Byzantine-tolerant implementation that guarantees eventual consistency. We then use our Byzantine-tolerant DSO (BDSO) implementation to provide consensus-free algorithmic solutions to the Atomic Appends and Atomic Adds (the analogous problem of atomic appends applied on G-Sets) problems, as well as to construct consensus-free Single-Writer BDLOs. We believe that the BDSO has applications beyond the above-mentioned problems.