BBCA-CHAIN: Low Latency, High Throughput BFT Consensus on a DAG

TL;DR

BBCA-CHAIN introduces a low latency, high throughput BFT consensus protocol leveraging a modified Byzantine Consistent Broadcast primitive, enabling direct commits on a causally ordered DAG without extra voting or communication overhead.

Contribution

It presents BBCA-CHAIN, a novel BFT consensus protocol that removes voting latency and enhances throughput by integrating a modified BCB primitive into a causally ordered DAG structure.

Findings

Eliminates voting latency in DAG-based protocols.

Achieves high throughput through parallel block proposals.

Provides a simple, specification-ready protocol for high-performance systems.

Abstract

This paper presents a partially synchronous BFT consensus protocol powered by BBCA, a lightly modified Byzantine Consistent Broadcast (BCB) primitive. BBCA provides a Complete-Adopt semantic through an added probing interface to allow either aborting the broadcast by correct nodes or exclusively, adopting the message consistently in case of a potential delivery. It does not introduce any extra types of messages or additional communication costs to BCB. BBCA is harnessed into BBCA-CHAIN to make direct commits on a chained backbone of a causally ordered graph of blocks, without any additional voting blocks or artificial layering. With the help of Complete-Adopt, the additional knowledge gained from the underlying BCB completely removes the voting latency in popular DAG-based protocols. At the same time, causal ordering allows nodes to propose blocks in parallel and achieve high throughput. BBCA-CHAIN thus closes up the gap between protocols built by consistent broadcasts (e.g., Bullshark) to those without such an abstraction (e.g., PBFT/HotStuff), emphasizing their shared fundamental principles. Using a Bracha-style BCB as an example, we fully specify BBCA-CHAIN with simplicity, serving as a solid basis for high-performance replication systems (and blockchains).