Sharding enhances blockchain scalability by dividing the network into shards, each managing specific unspent transaction outputs or accounts. As an introduced new transaction type, cross-shard transactions pose a critical challenge to the security and efficiency of sharding blockchains. Currently, there is a lack of a generic sharding consensus pattern that achieves both security and low overhead. In this paper, we present Kronos, a secure sharding blockchain consensus achieving optimized overhead. In particular, we propose a new secure sharding consensus pattern, based on a buffer managed jointly by shard members. Valid transactions are transferred to the payee via the buffer, while invalid ones are rejected through happy or unhappy paths. Kronos is proved to achieve security with atomicity under malicious clients with optimal intra-shard overhead $kB$ ($k$ for involved shard number and $B$ for a Byzantine fault tolerance (BFT) cost). Besides, we propose secure cross-shard certification methods based on batch certification and reliable cross-shard transfer. The former combines hybrid trees or vector commitments, while the latter integrates erasure coding. Handling $b$ transactions, Kronos is proved to achieve reliability with low cross-shard overhead $O(n b \lambda)$ ($n$ for shard size and $\lambda$ for the security parameter). Notably, Kronos imposes no restrictions on BFT and does not rely on time assumptions, offering optional constructions in various modules. We implement Kronos using two prominent BFT protocols: asynchronous Speeding Dumbo and partial synchronous Hotstuff. Extensive experiments demonstrate Kronos scales the consensus nodes to thousands, achieving a substantial throughput of 320 ktx/sec with 2.0 sec latency. Compared with the past solutions, Kronos outperforms, achieving up to a 12* improvement in throughput and a 50% reduction in latency.

翻译：摘要：分片通过将网络划分为多个分片来增强区块链的可扩展性，每个分片管理特定的未花费交易输出或账户。作为一种引入的新交易类型，跨分片交易对分片区块链的安全性和效率构成了关键挑战。目前，缺乏一种既能实现安全性又能保持低开销的通用分片共识模式。在本文中，我们提出了Kronos，一种实现了优化开销的安全分片区块链共识协议。具体而言，我们基于由分片成员共同管理的缓冲区，提出了一种新的安全分片共识模式。有效交易通过缓冲区转移给收款方，而无效交易则通过成功或失败路径被拒绝。Kronos被证明能够在恶意客户端下实现具有原子性的安全性，且具有最优的分片内开销$kB$（其中$k$为涉及的分片数量，$B$为拜占庭容错协议成本）。此外，我们提出了基于批量认证和可靠跨分片传输的安全跨分片认证方法。前者结合了混合树或向量承诺，后者则集成了纠删码。在处理$b$笔交易时，Kronos被证明能够实现可靠性，且跨分片开销为$O(n b \lambda)$（其中$n$为分片规模，$\lambda$为安全参数）。值得注意的是，Kronos对BFT协议不施加任何限制，也不依赖时间假设，并在各个模块中提供了可选构造。我们使用两种著名的BFT协议实现了Kronos：异步的Speeding Dumbo和部分同步的Hotstuff。大量实验表明，Kronos可将共识节点扩展至数千个，在2.0秒延迟下实现了显著的320 ktx/sec吞吐量。与以往方案相比，Kronos性能更优，吞吐量提升高达12倍，延迟降低50%。