Bicomp：一种双层可扩展的Nakamoto共识协议
Bicomp: A Bilayer Scalable Nakamoto Consensus Protocol
摘要：
区块链近年来受到了极大的关注，并在不同的场景中激发了创新。然而，影响其性能的许多重要问题仍然是开放的。例如，人们普遍认为，高水平的安全性和可扩展性以及完全的去中心化仍然不可能同时实现。在本文中，我们提出了Bicomp，一个双层可扩展的Nakamoto共识协议，这是一种基于高安全性和纯分散的Nakamoto共识的方法，并在可扩展性上有显着的改善。在Bicomp中，生成两种类型的块，即，用于网络中并发事务打包的微块和用于领导竞争和链形成的宏块。在每轮开始时，通过使用来自工作量证明的宏块报头来选举领导者。然后，选出的领导者在其任期内接收由不同节点挖掘的多个微块并将其打包成一个宏块，这导致双层块结构。这种设计限制了领导者的权力，并鼓励尽可能多的节点参与打包交易的过程，这促进了系统的分片性质。此外，还设计了几种机制来减少交易重叠，进一步限制领导者的权力，其中，在分叉时，除了最长链优先原则之外，还提出了一种新的基于交易多样性的度量标准作为选择合法链的第二级标准。Bicomp的安全问题和潜在的攻击进行了广泛的讨论和实验进行评估。从基于全球50个节点的实验结果来看，Bicomp在可扩展性上比比特币和以太坊有了显著的提高，同时仍然保留了安全性和去中心化的优点。
英文摘要：
Blockchain has received great attention in recent years and motivated innovations in different scenarios. However, many vital issues which affect its performance are still open. For example, it is widely convinced that high level of security and scalability and full decentralization are still impossible to achieve simultaneously. In this paper, we propose Bicomp, a bilayer scalable Nakamoto consensus protocol, which is an approach based on high security and pure decentralized Nakamoto consensus, and with a significant improvement on scalability. In Bicomp, two kinds of blocks are generated, i.e., microblocks for concurrent transaction packaging in network, and macroblocks for leadership competition and chain formation. A leader is elected at beginning of each round by using a macroblock header from proof-of-work. An elected leader then receives and packages multiple microblocks mined by different nodes into one macroblock during its tenure, which results in a bilayer block structure. Such design limits a leader's power and encourages as many nodes as possible to participate in the process of packaging transactions, which promotes the sharding nature of the system. Furthermore, several mechanisms are carefully designed to reduce transaction overlapping and further limit a leader's power, among which a novel transaction diversity based metric is proposed as the second level criteria besides the longest-chain-first principle on selecting a legitimate chain when fork happens. Security issues and potential attacks to Bicomp are extensively discussed and experiments for evaluation are performed. From the experimental results based on 50 nodes all over the world, Bicomp achieves significant improvement on scalability than that of Bitcoin and Ethereum, while the security and decentralization merits are still preserved.
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