No More Attacks on Proof-of-Stake Ethereum?

The latest message driven (LMD) greedy heaviest observed sub-tree (GHOST) consensus protocol is a critical component of future proof-of-stake (PoS) Ethereum. In its current form, the protocol is brittle and intricate to reason about, as evidenced by recent attacks, patching attempts, and G\"orli testnet reorgs. We present Goldfish, which can be seen as a considerably simplified variant of the current protocol, and prove that it is secure and reorg resilient in synchronous networks with dynamic participation, assuming a majority of the nodes (called validators) follows the protocol honestly. Furthermore, we show that subsampling validators can improve the communication efficiency of Goldfish, and that Goldfish is composable with finality gadgets and accountability gadgets. The aforementioned properties make Goldfish a credible candidate for a future protocol upgrade of PoS Ethereum, as well as a versatile pedagogical example. Akin to traditional propose-and-vote-style consensus protocols, Goldfish is organized into slots, at the beginning of which a leader proposes a block containing new transactions, and subsequently members of a committee take a vote towards block confirmation. But instead of using quorums, Goldfish is powered by a new mechanism that carefully synchronizes the inclusion and exclusion of votes in honest validators' views.