Modern blockchains guarantee that submitted transactions will be included eventually; a property formally known as liveness. But financial activity requires transactions to be included in a timely manner. Unfortunately, classical liveness is not strong enough to guarantee this, particularly in the presence of a motivated adversary who benefits from censoring transactions. We define censorship resistance as the amount it would cost the adversary to censor a transaction for a fixed interval of time as a function of the associated tip. This definition has two advantages, first it captures the fact that transactions with a higher miner tip can be more costly to censor, and therefore are more likely to swiftly make their way onto the chain. Second, it applies to a finite time window, so it can be used to assess whether a blockchain is capable of hosting financial activity that relies on timely inclusion. We apply this definition in the context of auctions. Auctions are a building block for many financial applications, and censoring competing bids offers an easy-to-model motivation for our adversary. Traditional proof-of-stake blockchains have poor enough censorship resistance that it is difficult to retain the integrity of an auction when bids can only be submitted in a single block. As the number of bidders $n$ in a single block auction increases, the probability that the winner is not the adversary, and the economic efficiency of the auction, both decrease faster than $1/n$. Running the auction over multiple blocks, each with a different proposer, alleviates the problem only if the number of blocks grows faster than the number of bidders. We argue that blockchains with more than one concurrent proposer have can have strong censorship resistance. We achieve this by setting up a prisoner's dilemma among the proposers using conditional tips.

翻译：现代区块链保证提交的交易最终会被包含在内，这一性质在形式上称为活性。但金融活动要求交易能够及时被纳入。不幸的是，经典的活性不足以确保这一点，尤其是在存在一个通过审查交易获利的动机明确的对手时。我们将抗审查能力定义为：对手为在固定时间间隔内审查一笔交易所需付出的成本，该成本是相关小费的函数。这一定义有两个优势：首先，它捕捉了这样一个事实——给予矿工更高小费的交易可能被审查的成本更高，因此更有可能迅速上链；其次，它适用于有限的时间窗口，因此可用于评估区块链是否能够承载依赖于及时纳入的金融活动。我们在拍卖的背景下应用这一定义。拍卖是许多金融应用的基础构件，而审查竞争出价为我们的对手提供了一个易于建模的动机。传统的权益证明区块链的抗审查能力较弱，以至于当出价只能在一个区块内提交时，很难保持拍卖的完整性。随着单区块拍卖中竞拍者数量 $n$ 的增加，胜出者不是对手的概率以及拍卖的经济效率均以快于 $1/n$ 的速度下降。如果拍卖跨多个区块进行，每个区块由不同的提议者生成，则只有当区块数的增长速度快于竞拍者数量时才能缓解该问题。我们认为，拥有多个并发提议者的区块链可能具备强大的抗审查能力。我们通过使用条件小费在提议者之间设置囚徒困境来实现这一点。