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

Rati Gelashvili, Lefteris Kokoris-Kogias, Alberto Sonnino, Alexander Spiegelman, Zhuolun Xiang

TL;DR

Ditto presents a practical Byzantine SMR that delivers linear communication on the happy path and quadratic fallback with guaranteed progress during asynchrony, by replacing view synchronization with an asynchronous MVBA-based fallback. Jolteon, a 2-chain variant of HotStuff, reduces commit latency and informs Ditto’s design, trading a quadratic view-change for faster steady-state operation. The authors implement and evaluate Jolteon and Ditto, showing Jolteon’s latency advantage over HotStuff and Ditto’s adaptability under faults, outperforming VABA in faultless scenarios and approaching 2-chain VABA performance under adversarial conditions. The results suggest breaking the robustness-efficiency trade-off is practical for real-world production systems."

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.

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

TL;DR

Ditto presents a practical Byzantine SMR that delivers linear communication on the happy path and quadratic fallback with guaranteed progress during asynchrony, by replacing view synchronization with an asynchronous MVBA-based fallback. Jolteon, a 2-chain variant of HotStuff, reduces commit latency and informs Ditto’s design, trading a quadratic view-change for faster steady-state operation. The authors implement and evaluate Jolteon and Ditto, showing Jolteon’s latency advantage over HotStuff and Ditto’s adaptability under faults, outperforming VABA in faultless scenarios and approaching 2-chain VABA performance under adversarial conditions. The results suggest breaking the robustness-efficiency trade-off is practical for real-world production systems."

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.

Paper Structure

This paper contains 41 sections, 22 theorems, 8 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Preliminaries
  3. Cryptographic primitives and assumptions.
  4. BFT SMR.
  5. Terminology
  6. Performance metrics.
  7. Description of DiemBFT.
  8. Jolteon Design
  9. Safety intuition.
  10. DiemBFT vs Jolteon.
  11. Efficiency.
  12. Limitations.
  13. Ditto Design
  14. Multi-valued Validated Byzantine Agreement
  15. Protocol intuition.
  16. ...and 26 more sections

Key Result

Theorem 1

During the periods of synchrony with honest leaders, the amortized communication complexity per block decision is $O(n)$, and the block-commit latency is $5$ rounds. During periods of asynchrony, the expected communication complexity per block decision is $O(n^2)$, and the expected block-commit late

Figures (8)

  • Figure 1: DiemBFT in our terminology.
  • Figure 2: Jolteon.
  • Figure 3: Ditto
  • Figure 4: Comparative block-commit latency for $3$-chain DiemBFT (HotStuff) and Jolteon. WAN measurements with 10, 20, or 50 replicas. No replica faults, 500KB mempool batch size and 512B transaction size.
  • Figure 5: Comparative throughput-latency performance for $3$-chain DiemBFT (HotStuff), Jolteon, Ditto, and $2$-chain VABA WAN measurements with 10, 20, or 50 replicas. No replica faults, 500KB mempool batch size and 512B transaction size.
  • ...and 3 more figures

Theorems & Definitions (45)

  • Theorem 1: Efficiency
  • proof
  • Definition 1: Global direct-commit
  • Lemma 1
  • proof
  • Lemma 2
  • proof
  • Lemma 3
  • proof
  • Theorem 2
  • ...and 35 more