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Thunderella: Blockchains with Optimistic Instant Confirmation

  • Rafael Pass
  • Elaine Shi
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 10821)

Abstract

State machine replication, or “consensus”, is a central abstraction for distributed systems where a set of nodes seek to agree on an ever-growing, linearly-ordered log. In this paper, we propose a practical new paradigm called Thunderella for achieving state machine replication by combining a fast, asynchronous path with a (slow) synchronous “fall-back” path (which only gets executed if something goes wrong); as a consequence, we get simple state machine replications that essentially are as robust as the best synchronous protocols, yet “optimistically” (if a super majority of the players are honest), the protocol “instantly” confirms transactions.

We provide instantiations of this paradigm in both permissionless (using proof-of-work) and permissioned settings. Most notably, this yields a new blockchain protocol (for the permissionless setting) that remains resilient assuming only that a majority of the computing power is controlled by honest players, yet optimistically—if 3/4 of the computing power is controlled by honest players, and a special player called the “accelerator”, is honest—transactions are confirmed as fast as the actual message delay in the network. We additionally show the 3/4 optimistic bound is tight for protocols that are resilient assuming only an honest majority.

Notes

Acknowledgments

We thank Jian Xie and Youcai Qian for inspiring conversations. We also thank Lorenzo Alvisi and Robbert van Renesse for helpful discussions and moral support. This work is supported in part by NSF grants CNS-1217821, CNS-1314857, CNS-1514261, CNS-1544613, CNS-1561209, CNS-1601879, CNS-1617676, AFOSR Award FA9550-15-1-0262, an Office of Naval Research Young Investigator Program Award, a Microsoft Faculty Fellowship, a Packard Fellowship, a Sloan Fellowship, Google Faculty Research Awards, and a VMWare Research Award.

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Copyright information

© International Association for Cryptologic Research 2018

Authors and Affiliations

  1. 1.CornellTechNew YorkUSA
  2. 2.CornellIthacaUSA

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