OptChain: Achieving Optimal Throughput of Permissionless Blockchains

2026-06-22

AI Summary

This work addresses the challenge of approaching the theoretical throughput limit in permissionless blockchains while preserving security and scalability. The authors propose OptChain, a novel protocol that, for the first time, asymptotically achieves the throughput upper bound of permissionless state machine replication (SMR) under a fixed failure probability. Its core innovation lies in a two-dimensional sharding optimization: vertically, the Shardis mechanism approaches the per-shard bandwidth limit, while horizontally, diffusion mining enables the maximum number of shards without compromising security. Evaluated on a multi-region AWS deployment, OptChain demonstrates significantly higher throughput than existing permissionless protocols, closely approaching the theoretical optimum.

Abstract

We introduce \textit{OptChain}, a permissionless blockchain state machine replication (SMR) protocol that achieves optimal throughput. We first establish a theoretical upper bound on the throughput of any SMR protocol under a fixed error probability, and OptChain is the first protocol to approach this limit. Conceptually, OptChain is a sharding protocol that optimizes both vertical and horizontal scalability. Vertically, we introduce \textit{Shardis}, a novel permissionless verifiable information dispersal mechanism that maximizes intra-shard throughput to its physical limit, determined by the fastest node's bandwidth within each shard. Horizontally, we propose \textit{diffusion mining}, which ensures security as long as each shard includes at least one honest node, thereby allowing for the maximum number of shards. We provide a formal security and efficiency analysis, demonstrating that OptChain approaches the established upper bound while maintaining robust security. Finally, we implement a full prototype of OptChain and deploy it on AWS EC2 nodes across various regions. Experimental results indicate that OptChain outperforms state-of-the-art permissionless protocols and closely approaches the theoretical optimal throughput.

Problem

• permissionless blockchain
• throughput optimization
• state machine replication
• sharding
• scalability

Innovation

• OptChain
• Shardis
• diffusion mining
• throughput optimization
• permissionless sharding