Parallel Proof-of-Work with Concrete Bounds

TL;DR

This paper introduces parallel proof-of-work protocols that significantly enhance security bounds over traditional sequential proof-of-work, enabling more secure state updates in distributed systems.

Contribution

It presents a novel family of parallel proof-of-work protocols with concrete failure bounds, improving security and efficiency in distributed consensus.

Findings

Parallel proof-of-work offers two orders of magnitude more security than sequential proof-of-work.

State updates can be securely committed after one block, reducing double-spending risks.

Simulations confirm robustness against assumption violations.

Abstract

Authorization is challenging in distributed systems that cannot rely on the identification of nodes. Proof-of-work offers an alternative gate-keeping mechanism, but its probabilistic nature is incompatible with conventional security definitions. Recent related work establishes concrete bounds for the failure probability of Bitcoin's sequential proof-of-work mechanism. We propose a family of state replication protocols using parallel proof-of-work. Our bottom-up design from an agreement sub-protocol allows us to give concrete bounds for the failure probability in adversarial synchronous networks. After the typical interval of 10 minutes, parallel proof-of-work offers two orders of magnitude more security than sequential proof-of-work. This means that state updates can be sufficiently secure to support commits after one block (i.e., after 10 minutes), removing the risk of double-spending in many applications. We offer guidance on the optimal choice of parameters for a wide range of network and attacker assumptions. Simulations show that the proposed construction is robust against violations of design assumptions.