Jolteon and Ditto: Network-Adaptive Efficient Consensus with Asynchronous Fallback

TL;DR

This paper introduces Ditto, a Byzantine SMR protocol that combines optimal communication efficiency with asynchronous progress guarantees, improving robustness and performance over existing protocols.

Contribution

We design Ditto, a novel Byzantine SMR protocol that achieves linear and quadratic communication costs on and off the happy path, with asynchronous fallback for robustness, building upon HotStuff.

Findings

Jolteon reduces HotStuff's latency by 200-300ms.

Ditto outperforms Jolteon under faults and VABA in faultless conditions.

The protocols are experimentally validated with improved performance.

Abstract

Existing committee-based Byzantine state machine replication (SMR) protocols, typically deployed in production blockchains, face a clear trade-off: (1) they either achieve linear communication cost in the happy path, but sacrifice liveness during periods of asynchrony, or (2) they are robust (progress with probability one) but pay quadratic communication cost. We believe this trade-off is unwarranted since existing linear protocols still have asymptotic quadratic cost in the worst case. We design Ditto, a Byzantine SMR protocol that enjoys the best of both worlds: optimal communication on and off the happy path (linear and quadratic, respectively) and progress guarantee under asynchrony and DDoS attacks. We achieve this by replacing the view-synchronization of partially synchronous protocols with an asynchronous fallback mechanism at no extra asymptotic cost. Specifically, we start from HotStuff, a state-of-the-art linear protocol, and gradually build Ditto. As a separate contribution and an intermediate step, we design a 2-chain version of HotStuff, Jolteon, which leverages a quadratic view-change mechanism to reduce the latency of the standard 3-chain HotStuff. We implement and experimentally evaluate all our systems. Notably, Jolteon's commit latency outperforms HotStuff by 200-300ms with varying system size. Additionally, Ditto adapts to the network and provides better performance than Jolteon under faulty conditions and better performance than VABA (a state-of-the-art asynchronous protocol) under faultless conditions. This proves our case that breaking the robustness-efficiency trade-off is in the realm of practicality.