Byzantine fault tolerant (BFT) consensus protocols are traditionally developed to support reliable distributed computing. For applications where the protocol participants are economic agents, recent works highlighted the importance of accountability: the ability to identify participants who provably violate the protocol. We propose to evaluate the security of an accountable protocol in terms of its liveness resilience, the minimum number of Byzantine nodes when liveness is violated, and its accountable safety resilience, the minimum number of accountable Byzantine nodes when safety is violated. We characterize the optimal tradeoffs between these two resiliences in different network environments, and identify an availability-accountability dilemma: in an environment with dynamic participation, no protocol can simultaneously be accountably-safe and live. We provide a resolution to this dilemma by constructing an optimally-resilient accountability gadget to checkpoint a longest chain protocol, such that the full ledger is live under dynamic participation and the checkpointed prefix ledger is accountable. Our accountability gadget construction is black-box and can use any BFT protocol which is accountable under static participation. Using HotStuff as the black box, we implemented our construction as a protocol for the Ethereum 2.0 beacon chain, and our Internet-scale experiments with more than 4000 nodes show that the protocol can achieve the required scalability and has better latency than the current solution Gasper, while having the advantage of being provably secure. To contrast, we demonstrate a new attack on Gasper.
翻译:诚然,容忍断层(BFT)共识协议(BFT)传统上是用来支持可靠的分配计算。对于议定书参与者是经济行为主体的应用程序,最近的工作强调了问责的重要性:能够识别哪些参与者明显违反协议。我们提议评估问责协议的安全性,从生存复原力角度评价问责协议的安全性。我们提议从生存复原力的角度评价拜占庭节点的最低数量,在生活能力被破坏时评价拜占庭节点的最低数量,安全被破坏时负责的比占庭节节点的最低数量。我们确定这两个在不同网络环境中的复原力之间的最佳取舍,并查明可获取性的两难点:在一个充满活力的参与环境中,任何协议都不能同时被问责。我们通过构建一个具有最佳弹性的问责制的问责机制来应对这一两难点。 我们通过构建一个具有最大弹性的问责制的问责机制来应对这一难题,而我们则通过构建一个比当前40度的互联网安全性协议更有利的地位,同时我们实施一个比40度的互联网安全性协议。