Jolteon and Ditto: Network-Adaptive Efficient Consensus with Asynchronous Fallback
This work addresses efficiency and robustness issues in blockchain consensus protocols, offering a practical solution for decentralized systems, though it builds incrementally on existing methods like HotStuff.
The paper tackles the trade-off in Byzantine state machine replication protocols between linear communication cost and liveness during asynchrony by designing Ditto, which achieves optimal communication (linear on happy path, quadratic off) and progress guarantee under asynchrony and DDoS attacks. As an intermediate step, Jolteon reduces HotStuff's latency by 200-300ms, and Ditto outperforms existing protocols under various conditions.
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.