A Secure Cross-Shard View-Change Protocol for Sharding Blockchains

A complete sharding blockchain consists of many vital components, the two most important of which are the intra-shard consensus algorithm and the cross-shard transaction processing method. The latter usually requires a two-phase commit protocol, which usually relies on the shard leaders to transfer critical messages among different shards. In the process, a leader might behave maliciously. In response to possible problems in cross-shard transaction processing, this paper makes the following contributions. First, this paper proposes a cross-shard transaction censorship attack that may be launched by a shard leader. The leader might behave honestly inside the shard while does not transfer key messages between the shards. Second, a cross-shard view-change protocol is proposed to defend against the attack. When a shard leader behaves maliciously between shards, a related shard’s members can run an intra-shard consensus algorithm to generate a proof of the leader’s malicious behavior and forward the proof to the corresponding shard’s members. The shard members could launch an intra-shard view-change operation to replace the malicious leader with a new one. Third, it is proved that the proposed protocol satisfies consistency and liveness. The secure cross-shard view-change protocol can be applied to most sharding blockchains to ensure the safe and efficient execution of cross-shard transactions.