HiCoCS: High Concurrency Cross-Sharding on Permissioned Blockchains

TL;DR

HiCoCS tackles the bottleneck of highly concurrent cross-shard transactions in permissioned blockchains by introducing virtual sub-brokers built from composite keys, enabling conflict-free batching without adding physical intermediaries. It combines AES-based pre-processing, CKKS fully homomorphic encryption for ciphertext-space aggregation, and a CKPoE-driven composite key reuse mechanism to reduce overhead. The prototype on Hyperledger Fabric demonstrates substantial improvements in TSR, TPS, and latency over baselines, while maintaining data confidentiality and eventual atomicity. This approach provides a practical, scalable cross-shard middleware with potential applicability to other blockchains that support composite keys and privacy-preserving operations, enabling enterprise-grade Web3 deployments.

Abstract

As the foundation of the Web3 trust system, blockchain technology faces increasing demands for scalability. Sharding emerges as a promising solution, but it struggles to handle highly concurrent cross-shard transactions (\textsf{CSTx}s), primarily due to simultaneous ledger operations on the same account. Hyperledger Fabric, a permissioned blockchain, employs multi-version concurrency control for parallel processing. Existing solutions use channels and intermediaries to achieve cross-sharding in Hyperledger Fabric. However, the conflict problem caused by highly concurrent \textsf{CSTx}s has not been adequately resolved. To fill this gap, we propose HiCoCS, a high concurrency cross-shard scheme for permissioned blockchains. HiCoCS creates a unique virtual sub-broker for each \textsf{CSTx} by introducing a composite key structure, enabling conflict-free concurrent transaction processing while reducing resource overhead. The challenge lies in managing large numbers of composite keys and mitigating intermediary privacy risks. HiCoCS utilizes virtual sub-brokers to receive and process \textsf{CSTx}s concurrently while maintaining a transaction pool. Batch processing is employed to merge multiple \textsf{CSTx}s in the pool, improving efficiency. We explore composite key reuse to reduce the number of virtual sub-brokers and lower system overhead. Privacy preservation is enhanced using homomorphic encryption. Evaluations show that HiCoCS improves cross-shard transaction throughput by 3.5-20.2 times compared to the baselines.

Figures (15)

• Figure 1: The MVCC conflict and a cross-shard example in Hyperledger Fabric.
• Figure 2: Hyperledger Fabric's transaction processing flow.
• Figure 3: System overview of HiCoCS.
• Figure 4: An example illustrating the HiCoCS.
• Figure 5: Building blocks of HiCoCS.

Theorems & Definitions (6)

• Theorem 1
• proof
• Theorem 2
• proof
• Theorem 3
• proof