OPERA: Reasoning about continuous common knowledge in asynchronous distributed systems
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This paper introduces a new family of consensus protocols, namely Lachesis-class denoted by L, for distributed networks with guaranteed Byzantine fault tolerance. Each Lachesis protocol L in L has complete asynchrony, is leaderless, has no round robin, no proof-of-work, and has eventual consensus. The core concept of our technology is the OPERA chain, generated by the Lachesis protocol. In the most general form, each node in Lachesis has a set of k neighbours of most preference. When receiving transactions a node creates and shares an event block with all neighbours. Each event block is signed by the hashes of the creating node and its k peers. The OPERA chain of the event blocks is a Directed Acyclic Graph (DAG); it guarantees practical Byzantine fault tolerance (pBFT). Our framework is then presented using Lamport timestamps and concurrent common knowledge. Further, we present an example of Lachesis consensus protocol L_0 of our framework. Our L_0 protocol can reach consensus upon 2/3 of all participants' agreement to an event block without any additional communication overhead. L_0 protocol relies on a cost function to identify k peers and to generate the DAG-based OPERA chain. By creating a binary flag table that stores connection information and share information between blocks, Lachesis achieves consensus in fewer steps than pBFT protocol for consensus.
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