On the Limits of Consensus under Dynamic Availability and Reconfiguration

2025-10-03

AI Summary

Proof-of-stake blockchains must guarantee consensus liveness and dynamic reconfiguration of validator sets under Dynamic Availability with Reconfiguration (DAR), yet existing protocols (e.g., Ouroboros, Snow White) rely on unrealistic assumptions such as social consensus or perpetual key evolution. Method: We first establish the necessary and sufficient adversarial conditions for achieving consensus under DAR. Introducing the lightweight assumption that honest validators immediately destroy their secret keys upon departure, we design an efficient, cryptographically secure reconfiguration bootstrapping primitive. Contribution/Results: Our protocol eliminates reliance on social coordination or long-term key management, simultaneously satisfying dynamic availability and infrequent reconfiguration requirements. It maintains liveness and safety even under large-scale transient offline scenarios. The work advances both the practical deployability and theoretical completeness of DAR-consensus systems.

Technology Category

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

Application Category

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

Abstract

Proof-of-stake blockchains require consensus protocols that support Dynamic Availability and Reconfiguration (so-called DAR setting), where the former means that the consensus protocol should remain live even if a large number of nodes temporarily crash, and the latter means it should be possible to change the set of operating nodes over time. State-of-the-art protocols for the DAR setting, such as Ethereum, Cardano's Ouroboros, or Snow White, require unrealistic additional assumptions, such as social consensus, or that key evolution is performed even while nodes are not participating. In this paper, we identify the necessary and sufficient adversarial condition under which consensus can be achieved in the DAR setting without additional assumptions. We then introduce a new and realistic additional assumption: honest nodes dispose of their cryptographic keys the moment they express intent to exit from the set of operating nodes. To add reconfiguration to any dynamically available consensus protocol, we provide a bootstrapping gadget that is particularly simple and efficient in the common optimistic case of few reconfigurations and no double-spending attempts.

Problem

• Establishing necessary adversarial conditions for DAR consensus
• Eliminating unrealistic assumptions in existing blockchain protocols
• Introducing secure reconfiguration via key disposal and bootstrapping

Innovation

• Identifies necessary adversarial condition for consensus
• Introduces honest node key disposal assumption
• Provides simple bootstrapping gadget for reconfiguration