SpiralShard: Highly Concurrent and Secure Blockchain Sharding via Linked Cross-shard Endorsement

TL;DR

SpiralShard is a blockchain sharding protocol that enhances concurrency and security by allowing smaller, more numerous shards with a linked endorsement process, significantly improving throughput in large networks.

Contribution

It introduces the Linked Cross-shard Endorsement protocol enabling secure operation with smaller, more numerous shards for higher concurrency.

Findings

Achieves 19x throughput gain over Harmony.

Supports more shards with larger malicious node fractions.

Ensures security through sequential intra-shard verification.

Abstract

Blockchain sharding improves the scalability of blockchain systems by partitioning the whole blockchain state, nodes, and transaction workloads into different shards. However, existing blockchain sharding systems generally suffer from a small number of shards, resulting in limited concurrency. The main reason is that existing sharding systems require large shard sizes to ensure security. To enhance the concurrency of blockchain sharding securely, we propose SpiralShard. The intuition is to allow the existence of some shards with a larger fraction of malicious nodes (i.e., corrupted shards), thus reducing shard sizes. SpiralShard can configure more and smaller shards for higher concurrency at the same network size. To ensure security with the existence of corrupted shards, we propose the Linked Cross-shard Endorsement (LCE) protocol. According to our LCE protocol, the blocks of each shard are sequentially verified and endorsed (via intra-shard consensus) by a group of shards before being finalized. As a result, a corrupted shard can eliminate forks with the help of the other shards. We implement SpiralShard based on Harmony and conduct extensive evaluations. Experimental results show that, compared with Harmony, SpiralShard achieves around 19x throughput gain under a large network size with 4,000+ nodes.