International Association
for Cryptologic Research

Sharding emerges as a promising solution to enhance blockchain scalability. However, it faces two critical limitations during shard reconfiguration: (1) the TPS-Degradation issue, arising from ledger synchronization conflicts during transaction processing, and (2) the Zero-TPS issue, caused by disruptions in transaction processing due to key negotiation. To this end, we propose Shardora, a blockchain sharding system for scaling blockchain by unleashing parallelism. In Shardora, we implement two essential mechanisms: (1) A parallelized dual committee framework with a reputation mechanism to mitigate the TPS-Degradation issue while ensuring system security. (2) A parallelized key pre-negotiation mechanism with a secret-reuse strategy to avoid the Zero-TPS issue while maintaining a continuously high TPS. We prove that Shardora offers theory-guaranteed security. We implement a prototype of Shardora and deploy it on Alibaba Cloud. Experimental results demonstrate that Shardora addresses the limitations by significantly reducing the overhead of both ledger synchronization and key negotiation, which outperforms state-of-the-art sharding schemes by at least 90%. In addition, Shardora shows its superior performance in terms of throughput and latency, achieving a peak throughput of 8300 TPS on a single shard with 600 nodes under LAN conditions. The code of Shardora is publicly available on GitHub.