RF-Chain: A rollback-free inter-shard transaction processing scheme against malicious brokers

To improve the transaction processing rate of blockchain, the existing sharding technology divides a blockchain network into subgroups (i.e., shard), and realizes intra-shard transaction processing locally and inter-shard transaction processing via intermediary accounts (i.e., brokers). However, if the inter-shard processing fails due to malicious brokers, the sharding technology has to carry out a rollback process for blockchain safety such that the transaction processing rate is decreased significantly. In this paper, we present a novel inter-shard transaction processing scheme called Rollback-free Blockchain (RF-Chain for short), which can process inter-shard transaction securely without rollbacks in the presence of malicious brokers. To this end, RF-Chain includes a Deposit Mechanism on a global smart contract, so as to refund the transaction victim if a malicious broker behavior is detected. We developed a RF-Chain prototype and conducted abundant experiments using real Ethereum transaction data. Compared with the existing rollback-based schemes, RF-Chain increases the transaction throughput by 98.3% and decreases the transaction confirmation latency by 85.1% in the presence of malicious activities using 3.7% communication overhead. Thus, RF-Chain can effectively mitigate malicious broker behaviors and achieve lightweight rollback-free processing.