NSshard: Low-Cross-Shard Sharding via Account Partitioning for Blockchain-Based IoT

The Internet of Things (IoT) links the physical world to computing systems, and blockchain presents an opportunity to address the issues of weak interoperability and security flaws within IoT. However, blockchain faces the challenge of low throughput and scalability. Sharding is a promising solution, but it divides the blockchain into multiple committees, making the attack cost of malicious nodes lower. Sharding also leads to a large number of cross-committee transactions, which degrades the system’s performance. In this article, we propose the NSshard sharding framework that provides secure and low-cross-committee scaling. NSshard consists of network sharding and state sharding. We first propose a reputation score-based network sharding, which assigns each node a reputation score to reward its honest verification of transactions and penalizes its malicious behavior. This network sharding uses a random but balanced distribution of reputation scores, thereby decreasing the risk of collusion. We also propose a graph-based account partitioning scheme for state partitioning. To reduce the amount of cross-committee transactions, the scheme uses an undirected weighted graph to depict accounts and transactions. We design two algorithms based on edge splitting and overlapping community discovery, respectively. We also propose a dynamic sharding method to handle new transactions. We conduct extensive experiments to evaluate the efficiency of the proposed framework based on Ethereum transaction data. The experimental results show that our proposed framework can reduce the number of cross-committee transactions by 34.8% at 128 committees compared to the Metis algorithm.