LinBFT: Linear-Communication Byzantine Fault Tolerance for Public Blockchains

TL;DR

LinBFT introduces a linear-communication Byzantine fault tolerance protocol for public blockchains, achieving deterministic safety and liveness with significantly reduced communication complexity compared to prior quadratic solutions.

Contribution

It presents the first O(n) deterministic BFT protocol for public blockchains, combining known techniques to improve efficiency and address permission-less system challenges.

Findings

Achieves amortized O(n) communication per block

Provides deterministic safety and liveness guarantees

Addresses permission-less blockchain issues like participant anonymity and dynamic sets

Abstract

This paper presents LinBFT, a novel Byzantine fault tolerance (BFT) protocol for blockchain systems that achieves amortized O(n) communication volume per block under reasonable conditions (where n is the number of participants), while satisfying determinist guarantees on safety and liveness. This significantly improves previous results, which either incurs quadratic communication complexity, or only satisfies safety in a probabilistic sense. LinBFT is based on the popular PBFT protocol, and cuts down its $O(n^4)$ complexity with three tricks, each by $O(n)$: linear view change, threshold signatures, and verifiable random functions. All three are known, i.e., the solutions are right in front of our eyes, and yet LinBFT is the first $O(n)$ solution with deterministic security guarantees. Further, LinBFT also addresses issues that are specific to permission-less, public blockchain systems, such as anonymous participants without a public-key infrastructure, proof-of-stake with slashing, rotating leader, and a dynamic participant set. In addition, LinBFT contains no proof-of-work module, reaches consensus for every block, and tolerates changing honesty of the participants for different blocks.