Slipstream: Ebb-and-Flow Consensus on a DAG with Fast Confirmation for UTXO Transactions

2024-10-18

arXiv.org

AI Summary

Achieving fast, irreversible transaction confirmation in Byzantine fault-tolerant (BFT) DAG-based UTXO ledgers remains challenging—particularly under high fault tolerance (up to 50% Byzantine nodes), while simultaneously ensuring both optimistic ordering liveness and strongly consistent final ordering, without relying on a global block sequence. Method: We propose Slipstream, a novel dual-mode BFT consensus protocol featuring a “tidal” two-tier ordering mechanism: optimistic ordering under the sleepy model (50% fault tolerance) and deterministic final ordering under the synchronous lock-step model (33% fault tolerance); a three-round synchronous transaction confirmation protocol decoupled from block ordering; and native double-spend suppression leveraging DAG topology. Results: In synchronous networks, UTXO transactions achieve irreversible confirmation in just three communication rounds—delivering high throughput, low latency, and provable security under standard BFT assumptions.

Technology Category

• Search and Optimization: Distributed Search
• Multiagent Systems: Mechanism Design
• Data Mining & Knowledge Management: Representing, Reasoning, and Using Provenance, Trust

Application Category

• Security and Privacy: Blockchains and distributed ledgers
• Systems and Infrastructure for Web, Mobile and WoT: Decentralized Web and Fediverse systems
• Responsible Web: Data and user privacy-enhancing technologies for the Web

Abstract

This paper introduces Slipstream, a Byzantine Fault Tolerance (BFT) protocol where nodes concurrently propose blocks to be added to a Directed Acyclic Graph (DAG) and aim to agree on block ordering. Slipstream offers two types of block orderings: an optimistic ordering, which is live and secure in a sleepy model under up to 50% Byzantine nodes, and a final ordering, which is a prefix of the optimistic ordering and ensures safety and liveness in an eventual lock-step synchronous model under up to 33% Byzantine nodes. Additionally, Slipstream integrates a payment system that allows for fast UTXO transaction confirmation independently of block ordering. Transactions are confirmed in three rounds during synchrony, and unconfirmed double spends are resolved in a novel way using the DAG structure.

Problem

• BFT protocol for DAG block ordering consensus
• Fast UTXO transaction confirmation in synchrony
• Resolving double spends using novel DAG structure

Innovation

• BFT protocol with concurrent block proposals on DAG
• Dual block ordering: optimistic and final for security
• Fast UTXO confirmation via DAG structure resolution