Afgjort: A Partially Synchronous Finality Layer for Blockchains
Afgjort: A Partially Synchronous Finality Layer for Blockchains
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DOI：
10.1007/978-3-030-57990-6_2
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发表时间：
2020-09
期刊：
影响因子：
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通讯作者：
Thomas Dinsdale-Young;Bernardo Magri;C. Matt;J. Nielsen;Daniel Tschudi
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作者：
Thomas Dinsdale-Young;Bernardo Magri;C. Matt;J. Nielsen;Daniel Tschudi
大多数现有的区块链要么依赖于Nakamoto风格的共识，其中链可以分叉并产生回滚，要么依赖于基于委员会的拜占庭容错（CBFT）共识，其中没有回滚。虽然后者提供了更好的一致性，但前者容忍更多的腐败。为了达到两全其美的效果，我们开始了终结层的正式研究。这样的finality层可以与Nakamoto风格的区块链（NSB）结合，并定期将区块声明为final，防止在final区块之外回滚。作为概念性贡献，我们正式定义了finality层的概念，并确定了以下属性对finality层至关重要：完成的块形成链（成链），各方就最终区块达成一致（协议），最后完成的区块不会落后于底层区块链中的最后一个区块（更新），并且所有最终确定的块在某个点已经在由持有共识所基于的资源的至少k个单元的诚实方所采用的链上，例如，作为我们的主要技术贡献，我们提出了最终层协议Afgjort。我们证明了它满足所有上述要求的设置中的终结器和部分同步的网络之间的腐败小于1/3。我们进一步表明，容忍小于1/3腐败是最佳的部分同步的终结层。最后，我们提供了使用我们的协议实现运行的实验数据;数据证实，比没有我们的终结层更快地达到终结。
Most existing blockchains either rely on a Nakamoto-style of consensus, where the chain can fork and produce rollbacks, or on a committee-based Byzantine fault tolerant (CBFT) consensus, where no rollbacks are possible. While the latter ones offer better consistency, the former tolerate more corruptions. To achieve the best of both worlds, we initiate the formal study of finality layers. Such a finality layer can be combined with a Nakamoto-style blockchain (NSB) and periodically declare blocks as final, preventing rollbacks beyond final blocks.As conceptual contributions, we formalize the concept of a finality layer and identify the following properties to be crucial for finality layers: finalized blocks form a chain (chain-forming), all parties agree on the finalized blocks (agreement), the last finalized block does not fall too far behind the last block in the underlying blockchain (updated), and all finalized blocks at some point have been on the chain adopted by honest parties holding at leastkunits of the resource on which consensus is based, e.g., stake or computing power (k-support).As our main technical contribution we propose the finality layer protocol Afgjort. We prove that it satisfies all of the aforementioned requirements in the setting with less than 1/3 corruption among the finalizers and a partially synchronous network.We further show that tolerating less than 1/3 corruption is optimal for partially synchronous finality layers. Finally, we provide data from experiments ran with an implementation of our protocol; the data confirms that finality is reached much faster than without our finality layer.