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Pipelet: Practical Streamlined Blockchain Protocol

Vivek Karihaloo, Ruchi Shah, Panruo Wu, Aron Laszka

TL;DR

Pipelet introduces a practical, streamlined BFT-style consensus protocol for permissioned blockchains that extends the simple Streamlet approach with clock synchronization and a stable proposer. It achieves $O(N)$ message complexity per finalized block in the normal case by eliminating implicit echoing, while preserving the notarization and finalization rules that ensure determinism and immutability. The protocol provides formal consistency and liveness guarantees under partial synchrony, and supports practical features such as epoch-based progression and explicit block synchronization to prevent network partitioning. Empirical comparisons show Pipelet offering lower messaging and scalable performance relative to Streamlet and PaLa in typical network conditions, while maintaining a small, verifiable design.

Abstract

Fueled by the growing popularity of proof-of-stake blockchains, there has been increasing interest and progress in permissioned consensus protocols, which could provide a simpler alternative to existing protocols, such as Paxos and PBFT. In particular, the recently proposed Streamlet protocol provides a surprisingly simple and streamlined consensus approach, which crystallizes years of research in simplifying and improving classical consensus protocols. While the simplicity of Streamlet is a major accomplishment, the protocol lacks certain practical features, such as supporting a stable block proposer, and it makes strong assumptions, such as synchronized clocks and the implicit echoing of all messages. Most importantly, it requires sending $O(N^3)$ messages per block in a network of $N$ nodes, which poses a significant challenge to its application in larger networks. To address these limitations, we introduce Pipelet, a practical streamlined consensus protocol. Pipelet employs the same block-finalization rule as Streamlet, but attains state-of-the-art performance in terms of communication complexity and provides features that are crucial for practical applications, such as clock synchronization and stable block proposers. At the same time, Pipelet retains the simplicity of Streamlet, which presents significant practical advantages, such as ease of implementation and verification.

Pipelet: Practical Streamlined Blockchain Protocol

TL;DR

Pipelet introduces a practical, streamlined BFT-style consensus protocol for permissioned blockchains that extends the simple Streamlet approach with clock synchronization and a stable proposer. It achieves message complexity per finalized block in the normal case by eliminating implicit echoing, while preserving the notarization and finalization rules that ensure determinism and immutability. The protocol provides formal consistency and liveness guarantees under partial synchrony, and supports practical features such as epoch-based progression and explicit block synchronization to prevent network partitioning. Empirical comparisons show Pipelet offering lower messaging and scalable performance relative to Streamlet and PaLa in typical network conditions, while maintaining a small, verifiable design.

Abstract

Fueled by the growing popularity of proof-of-stake blockchains, there has been increasing interest and progress in permissioned consensus protocols, which could provide a simpler alternative to existing protocols, such as Paxos and PBFT. In particular, the recently proposed Streamlet protocol provides a surprisingly simple and streamlined consensus approach, which crystallizes years of research in simplifying and improving classical consensus protocols. While the simplicity of Streamlet is a major accomplishment, the protocol lacks certain practical features, such as supporting a stable block proposer, and it makes strong assumptions, such as synchronized clocks and the implicit echoing of all messages. Most importantly, it requires sending messages per block in a network of nodes, which poses a significant challenge to its application in larger networks. To address these limitations, we introduce Pipelet, a practical streamlined consensus protocol. Pipelet employs the same block-finalization rule as Streamlet, but attains state-of-the-art performance in terms of communication complexity and provides features that are crucial for practical applications, such as clock synchronization and stable block proposers. At the same time, Pipelet retains the simplicity of Streamlet, which presents significant practical advantages, such as ease of implementation and verification.
Paper Structure (59 sections, 11 theorems, 6 figures, 2 tables, 3 algorithms)

This paper contains 59 sections, 11 theorems, 6 figures, 2 tables, 3 algorithms.

Table of Contents

  1. Introduction
  2. Overview of Pipelet
  3. Related Work
  4. Permissioned Blockchains
  5. Consensus Protocol Performance
  6. Assumptions, Objectives, and Threat Model
  7. Assumptions
  8. Proposer and Voting Nodes
  9. Cryptographic Primitives
  10. Timing and Communications
  11. Objectives
  12. Threat Model
  13. Pipelet Data Structures and Messages
  14. Data Structures
  15. Block
  16. ...and 44 more sections

Key Result

Theorem 1

Let us assume the following: (a) more than $\frac{2}{3} |N|$ nodes are honest, (b) $\mathcal{C}'$ is the finalized chain of an honest node, and $\mathcal{C}"$ is the finalized chain of another honest node. Then, it must hold that either $\mathcal{C}'$ and $\mathcal{C}"$ are the exact same chain, or

Figures (6)

  • Figure 1: Process of clock and block synchronization.
  • Figure 2: Process of block proposal and voting.
  • Figure 3: Messages per finalized blocks for average delay of 0.5.
  • Figure 4: Messages per finalized blocks for average delay of 2.
  • Figure 5: Time per finalized blocks for average delay of 0.5.
  • ...and 1 more figures

Theorems & Definitions (14)

  • Definition 1: Period of Synchrony
  • Definition 2: Consistency
  • Definition 3: Liveness
  • Theorem 1
  • Theorem 2
  • lemma 1: Uniqueness of each sequence number
  • lemma 2
  • lemma 3
  • lemma 4: Progress in periods of synchrony
  • lemma 5
  • ...and 4 more