Building a Verifiable Logical Clock for P2P Networks

TL;DR

The paper introduces Verifiable Logical Clocks (VLC) and Chrono to enable causality-aware computation in open P2P networks with Byzantine participants. It defines Init and Update operations that build a partial order while attaching verifiable proofs, enabling recursive verification across inputs. A modular validator abstraction supports multiple backends (Quorum Certificate, Trusted Hardware, and Verifiable Computation), offering security-performance trade-offs. The authors demonstrate two use cases—mutual exclusion and causally consistent data stores—and show Chrono achieves competitive latency and high throughput, outperforming traditional BFT total-order protocols in several scenarios. These results indicate Chrono as a practical framework for building decentralized applications with strong causal guarantees in adversarial environments.

Abstract

Logical clocks are a fundamental tool to establish causal ordering of events in a distributed system. They have been applied in weakly consistent storage systems, causally ordered broadcast, distributed snapshots, deadlock detection, and distributed system debugging. However, prior logical clock constructs fail to work in an open network with Byzantine participants. In this work, we present Chrono, a novel logical clock system that targets such challenging environment. We first redefine causality properties among distributed processes under the Byzantine failure model. To enforce these properties, Chrono defines a new validator abstraction for building fault-tolerant logical clocks. Furthermore, our validator abstraction is customizable: Chrono includes multiple backend implementations for the abstraction, each with different security-performance trade-offs. We have applied Chrono to build two decentralized applications, a mutual exclusive service and a weakly consistent key-value store. Chrono adds only marginal overhead compared to systems that tolerate no Byzantine faults. It also out-performs state-of-the-art BFT total order protocols by significant margins.

Figures (11)

• Figure 1: A motivating example.
• Figure 2: Chrono overview.
• Figure 3: Validator backends.
• Figure 4: Design of verifiable computation based validator backend.
• Figure 5: Resource acquisition latencies in the mutex use case.