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An Approach to Optimizing the VABA Protocol Using $κ$-size Committee

Nasit S Sony

TL;DR

The paper tackles the inefficiency of fully broadcasting requests in asynchronous Byzantine agreement by introducing Efficient-VABA (eVABA), which confines proposals to a randomly selected κ-sized committee that contains at least one honest party with high probability under the $n=3f+1$ resilience bound. It combines committee selection with a prioritized provable-broadcast (P-PB), propose-suggest workflow, and a leader-evidence mapping to ensure the leader is a committee member, enabling efficient view-change and termination. The approach yields strong security guarantees through PB properties, threshold signatures, and threshold coin-tossing, while achieving constant expected rounds and improved message complexity roughly on the order of $O(n^2)$ messages. This committee-based reduction preserves the essential safety and liveness of VABA and offers practical benefits for fault-tolerant state machine replication in asynchronous networks.

Abstract

Byzantine agreement protocols in asynchronous networks have gained renewed attention due to their independence from network timing assumptions to ensure termination. Traditional asynchronous Byzantine agreement protocols require every party to broadcast its requests (e.g., transactions), leading to high communication costs as parties ultimately agree on one party's request. This inefficiency is particularly significant in multi-valued Byzantine agreement protocols, where parties aim to agree on one party's requests under the assumption $n=3f+1$, where $n$ is the total number of parties, and $f$ is the number of Byzantine parties. To address these inefficiencies, we propose Efficient-VABA (eVABA), an optimized protocol for the asynchronous Byzantine agreement (ABA) problem. By limiting broadcasts to a selected subset of parties, the protocol reduces the number of messages and computation overhead.

An Approach to Optimizing the VABA Protocol Using $κ$-size Committee

TL;DR

The paper tackles the inefficiency of fully broadcasting requests in asynchronous Byzantine agreement by introducing Efficient-VABA (eVABA), which confines proposals to a randomly selected κ-sized committee that contains at least one honest party with high probability under the resilience bound. It combines committee selection with a prioritized provable-broadcast (P-PB), propose-suggest workflow, and a leader-evidence mapping to ensure the leader is a committee member, enabling efficient view-change and termination. The approach yields strong security guarantees through PB properties, threshold signatures, and threshold coin-tossing, while achieving constant expected rounds and improved message complexity roughly on the order of messages. This committee-based reduction preserves the essential safety and liveness of VABA and offers practical benefits for fault-tolerant state machine replication in asynchronous networks.

Abstract

Byzantine agreement protocols in asynchronous networks have gained renewed attention due to their independence from network timing assumptions to ensure termination. Traditional asynchronous Byzantine agreement protocols require every party to broadcast its requests (e.g., transactions), leading to high communication costs as parties ultimately agree on one party's request. This inefficiency is particularly significant in multi-valued Byzantine agreement protocols, where parties aim to agree on one party's requests under the assumption , where is the total number of parties, and is the number of Byzantine parties. To address these inefficiencies, we propose Efficient-VABA (eVABA), an optimized protocol for the asynchronous Byzantine agreement (ABA) problem. By limiting broadcasts to a selected subset of parties, the protocol reduces the number of messages and computation overhead.

Paper Structure

This paper contains 16 sections, 2 theorems, 1 figure, 1 algorithm.

Table of Contents

  1. Introduction
  2. Challenges and Proposed Solutions
  3. Our Contribution
  4. The Design of eVABA
  5. Committee Selection
  6. Proposal-Promotion
  7. Prioritized probable broadcast (P-PB)
  8. Propose-Suggest
  9. Party Selection
  10. Mapping to a selected party
  11. View-Change
  12. Security and Efficiency Analysis
  13. Security Analysis
  14. Prioritized provable-broadcast
  15. Efficiency Analysis
  16. ...and 1 more sections

Key Result

Lemma 3.1

Algorithm P-PB-D satisfies the selected property.

Figures (1)

  • Figure 1: eVABA illustration. Parties select a committee, and each committee member promotes its requests using the 4-step promotion. Then, a party proposes the proposal $p_i$ with proof $ts$. After receiving a proposal, each party suggests the proposal and waits for $\langle n-f \rangle$ suggestions. Then, the selected parties move to the party-selection and view-change step.

Theorems & Definitions (3)

  • Lemma 3.1
  • proof
  • Theorem 3.2