Optimizing Communication in Byzantine Agreement Protocols with Slim-HBBFT

TL;DR

The paper addresses the high communication overhead of Byzantine agreement in asynchronous networks when every party broadcasts all requests. It introduces Slim-HBBFT, an atomic broadcast protocol that achieves agreement over a subset of $q$ requests with a committee of size $\kappa = f+1$ and a Prioritized Provable Broadcast (P-PB) that emits proofs only for selected parties. It combines a propose/suggest flow with threshold encryption to preserve totality and prevent censorship, reducing communication complexity by a factor of $O(n)$. The work provides a security analysis showing ACS properties hold under standard BA assumptions and outlines avenues for simulation and dynamic committee sizing as future work.

Abstract

Byzantine agreement protocols in asynchronous networks have received renewed interest because they do not rely on network behavior to achieve termination. Conventional asynchronous Byzantine agreement protocols require every party to broadcast its requests (e.g., transactions), and at the end of the protocol, parties agree on one party's request. If parties agree on one party's requests while exchanging every party's request, the protocol becomes expensive. These protocols are used to design an atomic broadcast (ABC) protocol where parties agree on $\langle n-f \rangle$ parties' requests (assuming $n=3f+1$, where $n$ is the total number of parties, and $f$ is the number of Byzantine parties). Although the parties agree on a subset of requests in the ABC protocol, if the requests do not vary (are duplicated), investing in a costly protocol is not justified. We propose Slim-HBBFT, an atomic broadcast protocol that considers requests from a fraction of $n$ parties and improves communication complexity by a factor of $O(n)$. At the core of our design is a prioritized provable-broadcast (P-PB) protocol that generates proof of broadcast only for selected parties. We use the P-PB protocol to design the Slim-HBBFT atomic broadcast protocol. Additionally, we conduct a comprehensive security analysis to demonstrate that Slim-HBBFT satisfies the properties of the Asynchronous Common Subset protocol, ensuring robust security and reliability.

Figures (1)

• Figure 1: Slim-HBBFT illustration. Each selected party promotes its request using the P-PB protocol. After completing the P-PB protocol, a party broadcasts the requests with proof $ts$ as a proposal. Upon receiving a proposal, each party suggests it and waits for $\langle n-f \rangle$ suggestions, then runs the $ABA$ protocol as input.

Theorems & Definitions (5)

• Lemma 3.1
• proof
• Lemma 3.2
• proof
• Theorem 3.3