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SpiralShard: Highly Concurrent and Secure Blockchain Sharding via Linked Cross-shard Endorsement

You Lin, Mingzhe Li, Jin Zhang

TL;DR

The paper tackles blockchain scalability by rethinking shard security: instead of forcing all shards to be cryptographically honest, SpiralShard permits a fraction of corrupted shards and employs a Linked Cross-shard Endorsement (LCE) protocol to secure finality across shards. By organizing shards into endorsement groups and enforcing sequential cross-shard endorsements, the design preserves safety and liveness while enabling much finer, more numerous shards. The authors provide probabilistic analysis to tune shard and group sizes, demonstrate strong security guarantees under partial-synchronous networks, and report up to ~19–20x throughput gains over Harmony in a large-scale deployment. This approach significantly improves transaction concurrency in sharded blockchains and offers practical scalability for large networks with realistic adversaries.

Abstract

Blockchain sharding improves the scalability of blockchain systems by partitioning the whole blockchain state, nodes, and transaction workloads into different shards. However, existing blockchain sharding systems generally suffer from a small number of shards, resulting in limited concurrency. The main reason is that existing sharding systems require large shard sizes to ensure security. To enhance the concurrency of blockchain sharding securely, we propose SpiralShard. The intuition is to allow the existence of some shards with a larger fraction of malicious nodes (i.e., corrupted shards), thus reducing shard sizes. SpiralShard can configure more and smaller shards for higher concurrency at the same network size. To ensure security with the existence of corrupted shards, we propose the Linked Cross-shard Endorsement (LCE) protocol. According to our LCE protocol, the blocks of each shard are sequentially verified and endorsed (via intra-shard consensus) by a group of shards before being finalized. As a result, a corrupted shard can eliminate forks with the help of the other shards. We implement SpiralShard based on Harmony and conduct extensive evaluations. Experimental results show that, compared with Harmony, SpiralShard achieves around 19x throughput gain under a large network size with 4,000+ nodes.

SpiralShard: Highly Concurrent and Secure Blockchain Sharding via Linked Cross-shard Endorsement

TL;DR

The paper tackles blockchain scalability by rethinking shard security: instead of forcing all shards to be cryptographically honest, SpiralShard permits a fraction of corrupted shards and employs a Linked Cross-shard Endorsement (LCE) protocol to secure finality across shards. By organizing shards into endorsement groups and enforcing sequential cross-shard endorsements, the design preserves safety and liveness while enabling much finer, more numerous shards. The authors provide probabilistic analysis to tune shard and group sizes, demonstrate strong security guarantees under partial-synchronous networks, and report up to ~19–20x throughput gains over Harmony in a large-scale deployment. This approach significantly improves transaction concurrency in sharded blockchains and offers practical scalability for large networks with realistic adversaries.

Abstract

Blockchain sharding improves the scalability of blockchain systems by partitioning the whole blockchain state, nodes, and transaction workloads into different shards. However, existing blockchain sharding systems generally suffer from a small number of shards, resulting in limited concurrency. The main reason is that existing sharding systems require large shard sizes to ensure security. To enhance the concurrency of blockchain sharding securely, we propose SpiralShard. The intuition is to allow the existence of some shards with a larger fraction of malicious nodes (i.e., corrupted shards), thus reducing shard sizes. SpiralShard can configure more and smaller shards for higher concurrency at the same network size. To ensure security with the existence of corrupted shards, we propose the Linked Cross-shard Endorsement (LCE) protocol. According to our LCE protocol, the blocks of each shard are sequentially verified and endorsed (via intra-shard consensus) by a group of shards before being finalized. As a result, a corrupted shard can eliminate forks with the help of the other shards. We implement SpiralShard based on Harmony and conduct extensive evaluations. Experimental results show that, compared with Harmony, SpiralShard achieves around 19x throughput gain under a large network size with 4,000+ nodes.
Paper Structure (27 sections, 2 theorems, 12 equations, 8 figures, 3 tables)

This paper contains 27 sections, 2 theorems, 12 equations, 8 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Related Work and Motivation
  3. Blockchain and Blockchain Sharding
  4. Shard Size and Concurrency
  5. Network and Threat Model
  6. Network Model
  7. Threat Model
  8. System Overview and Objectives
  9. Overview of Main Designs
  10. Objectives
  11. Overview of Other Components
  12. Analysis and Discussion
  13. Epoch Failure Probability Analysis
  14. Protocol Security Analysis
  15. Corner Cases Discussion
  16. ...and 12 more sections

Key Result

Theorem 1

The LCE protocol provides safety if each corrupted shard has less than $2/3$ malicious nodes (i.e., less than $1/3$ fraction of Byzantine nodes plus no more than $1/3$ fraction of a-b-c nodes) and at least one honest shard exists in each endorsement group (i.e., each endorsement group has less than

Figures (8)

  • Figure 1: Linked Cross-shard Endorsement for $Shard_i$.
  • Figure 2: System architecture.
  • Figure 3: Performance comparison under various network sizes.
  • Figure 4: Performance under various shard sizes.
  • Figure 5: Consensus time comparsion.
  • ...and 3 more figures

Theorems & Definitions (4)

  • Theorem 1
  • proof
  • Theorem 2
  • proof