Towards Efficient and Secure Sharding-Based Blockchain

The Hong Kong University of Science and Technology
Department of Computer Science and Engineering


PhD Thesis Defence


Title: "Towards Efficient and Secure Sharding-Based Blockchain"

By

Mr. Mingzhe LI


Abstract

Blockchain technology, despite its growing importance, has been argued for its 
poor scalability. Sharding has become an effective approach to addressing the 
scalability issue faced in the blockchain. It divides nodes into multiple 
groups (shards) so that they can process transactions in parallel. However, the 
efficiency and security in existing blockchain sharding systems, despite being 
the basic design objectives, still suffer from many problems. To address these 
issues and achieve an efficient and secure blockchain sharding system, this 
thesis makes the following contributions.

First, existing blockchain sharding protocols do not scale well when tackling 
smart contracts (functions executing various logic). We present Jenga, a novel 
sharding-based approach for efficient smart contract processing. It requires 
all shards to share the logic for all contracts, hence multiple smart contracts 
can be executed within one round. Moreover, different shards store distinct 
states (state shards), and several orthogonal execution channels are 
established based on the state shards to reduce cross-shard communication. We 
implement Jenga and evaluation results illustrate that it achieves more than 
1.5x throughput gain compared to the existing cutting-edge work.

Second, existing works, for security, tend to configure large shard sizes to 
maintain a small fraction of intra-shard malicious nodes, at an expense of 
limited concurrency. This leads to limited concurrency. Therefore, we propose 
CoChain, a highly concurrent and recoverable blockchain sharding system. It 
allows shards to have a larger fraction of malicious nodes (up to 2/3), thus 
reducing the shard size and increasing concurrency. To ensure security, CoChain 
requires shards to monitor each other, hence a shard with a high fraction of 
malicious nodes can recover from failure with the help of other shards. We 
implement CoChain based on Harmony and experimental results show that CoChain 
achieves a 35x throughput gain compared with Harmony.

Third, existing blockchain sharding, during intra-shard consensus and 
cross-shard transaction processing, either faces security issues or sacrifices 
great performance for security. Therefore, we propose SS-Chain for enhanced 
intra/cross-shard security and per- formance. We design pipelined consensus 
with less communication overhead to improve intra-shard consensus efficiency 
and defend against attacks via frequent leader rotations. We attach proofs to 
cross-shard transactions to ensure cross-shard security and improve efficiency 
through transaction batching and proof pruning. We implement SS-Chain and 
large-scale evaluation results demonstrate that it achieves a throughput of 
more than 10,000 tx/sec even under malicious behaviors.


Date:			Wednesday, 6 July 2022

Time:			10:00am - 12:00noon

Zoom Meeting: 
https://hkust.zoom.us/j/95645462461?pwd=NWVpMlJmT3FiK3Q5cjJpRlhHL1lldz09

Chairperson:		Prof. Tim TSE (CIVL)

Committee Members:	Prof. Wei WANG (Supervisor)
 			Prof. Jin ZHANG (Supervisor)
 			Prof. Gary CHAN
 			Prof. Shuai WANG
 			Prof. Vincent LAU (ECE)
 			Prof. Cong WANG (CityU)


**** ALL are Welcome ****