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An efficient validated asynchronous byzantine agreement protocol using committee

Nasit S Sony

TL;DR

This work addresses asynchronous Byzantine agreement under adversarial faults by introducing a validated asynchronous BA (VABA) that uses a stochastic committee to reduce broadcasting and computation. The main method combines a committee-selection protocol, prioritized four-step provable-broadcast (P-PB) invocations, leader-election, and a mapping of the elected leader to a committee member, yielding Efficient-VABA with strong safety and liveness guarantees. The key contributions are the committee-based reduction in message complexity, the Propose-Suggest and mapping mechanisms to ensure progress from a small broadcast set, and formal security and efficiency analyses that show termination and optimal message/communication costs. The approach offers practical benefits for scalable fault-tolerant consensus in asynchronous networks, with potential extensions to further reduce remaining $n\!-to!-n$ communications and enhance performance.

Abstract

We present a Byzantine agreement protocol to address the inefficiencies inherent in multi-valued Byzantine agreement protocols, i.e., a version of the Byzantine agreement protocol where every party broadcasts its request, and at the end of the protocol, every party agrees on one of the party's requests. The protocol we present is a validated asynchronous Byzantine agreement protocol, i.e., a party's request must be validated by some external validity property before it is proposed for agreement. Differently from most of the MVBA protocols, we allow only a subset of total parties to broadcast their requests instead of all, and we make the subset selection stochastic each time the parties choose to broadcast a new set of requests. Then, at the time of the agreement, we choose a party from the selected subset, and the parties reach an agreement on the selected party's broadcast. Extensive theoretical analysis shows that this approach can produce efficient output regarding messages and computation overhead, but the protocol is time-consuming.

An efficient validated asynchronous byzantine agreement protocol using committee

TL;DR

This work addresses asynchronous Byzantine agreement under adversarial faults by introducing a validated asynchronous BA (VABA) that uses a stochastic committee to reduce broadcasting and computation. The main method combines a committee-selection protocol, prioritized four-step provable-broadcast (P-PB) invocations, leader-election, and a mapping of the elected leader to a committee member, yielding Efficient-VABA with strong safety and liveness guarantees. The key contributions are the committee-based reduction in message complexity, the Propose-Suggest and mapping mechanisms to ensure progress from a small broadcast set, and formal security and efficiency analyses that show termination and optimal message/communication costs. The approach offers practical benefits for scalable fault-tolerant consensus in asynchronous networks, with potential extensions to further reduce remaining communications and enhance performance.

Abstract

We present a Byzantine agreement protocol to address the inefficiencies inherent in multi-valued Byzantine agreement protocols, i.e., a version of the Byzantine agreement protocol where every party broadcasts its request, and at the end of the protocol, every party agrees on one of the party's requests. The protocol we present is a validated asynchronous Byzantine agreement protocol, i.e., a party's request must be validated by some external validity property before it is proposed for agreement. Differently from most of the MVBA protocols, we allow only a subset of total parties to broadcast their requests instead of all, and we make the subset selection stochastic each time the parties choose to broadcast a new set of requests. Then, at the time of the agreement, we choose a party from the selected subset, and the parties reach an agreement on the selected party's broadcast. Extensive theoretical analysis shows that this approach can produce efficient output regarding messages and computation overhead, but the protocol is time-consuming.
Paper Structure (34 sections, 16 theorems, 1 figure, 10 algorithms)

This paper contains 34 sections, 16 theorems, 1 figure, 10 algorithms.

Table of Contents

  1. Introduction
  2. Challenges and Proposed Solutions
  3. Our Contribution
  4. System Model
  5. Computation.
  6. Communications.
  7. Design Goal
  8. Validated asynchronous byzantine agreement (VABA)
  9. Preliminaries
  10. Provable-Broadcast.
  11. Threshold signature scheme:
  12. Threshold coin-tossing:
  13. $(1, \kappa, \epsilon)$- Committee Selection
  14. Committee Selection Properties.
  15. Proof for Validity property.
  16. ...and 19 more sections

Key Result

Lemma 3.1

(Validity of Committee Selection.) If $n=3f+1$, $f+1 \leq f$ and CE(id) returns a set $C$ containing at least one honest party except with $exp(-\epsilon(\kappa))$ probability.

Figures (1)

  • Figure 1: An overview of the proposed protocol.

Theorems & Definitions (25)

  • definition 2.1: Validated byzantine agreement
  • Lemma 3.1
  • proof
  • Lemma 5.1
  • proof
  • Lemma 5.2
  • proof
  • Lemma 5.3
  • Lemma 5.4
  • Lemma 5.5
  • ...and 15 more