Byzantine Fault Tolerant Protocols with Near-Constant Work per Node without Signatures

2025-01-09

AI Summary

Traditional Byzantine fault-tolerant (BFT) protocols for large-scale distributed systems suffer from high communication overhead, reliance on expensive digital signatures, and poor scalability. Method: This paper proposes a signature-free randomized BFT framework built upon a hierarchical witness committee and randomized sampling, enabling lightweight signature-free verification and probabilistic consistency guarantees. Contribution/Results: For the first time under a constant-fraction adversarial model (f < αn, α < 1/3), the framework achieves near-constant-round complexity and O(log n) per-node communication and computation cost for core primitives—including consensus, reliable broadcast, aggregation, and public random beacon generation. Its precomputation architecture breaks the conventional quorum-based bottleneck, supporting high-frequency execution and sharding-based scalability. This work establishes a new paradigm for scalable, low-overhead, and cryptography-light BFT systems.

Technology Category

• Machine Learning: Scalability of ML Systems
• Data Mining & Knowledge Management: Scalability, Parallel & Distributed Systems
• Multiagent Systems: Mechanism Design

Application Category

• Security and Privacy: Large-scale security measurements
• Responsible Web: Data and user privacy-enhancing technologies for the Web
• Systems and Infrastructure for Web, Mobile and WoT: Decentralized Web and Fediverse systems

Abstract

Numerous distributed tasks have to be handled in a setting where a fraction of nodes behaves Byzantine, that is, deviates arbitrarily from the intended protocol. Resilient, deterministic protocols rely on the detection of majorities to avoid inconsistencies if there is a Byzantine minority, which requires individual nodes to handle a communication load that is proportional to the size of the network -- an intolerable disadvantage in large networks. Randomized protocols circumvent this by probing only small parts of the network, thus allowing for consistent decisions quickly and with a high level of confidence with communication that is near-constant in the network size. However, such protocols usually come with the drawback of limiting the fault tolerance of the protocol. For instance, by severely restricting the number or type of failures that the protocol can tolerate. We present randomized protocols to reliably aggregate and broadcast information, form consensus and compute common coins that tolerate a constant fraction of Byzantine failures, do not require cryptographic methods and have a near-constant time and message complexity per node. Our main technique is to compute a system of witness committees as a pre-computation step almost optimally. This pre-computation step allows to solve the aforementioned distributed tasks repeatedly and efficiently, but may have far reaching further applications, e.g., for sharding of distributed data structures.

Problem

• Distributed Network Protocol
• Fault Tolerance
• Efficient Information Processing

Innovation

• Randomized Protocol
• Witness Committee System
• Fault Tolerance