Spamming attacks are a serious concern for consensus protocols, as witnessed by recent outages of a major blockchain, Solana. They cause congestion and excessive message delays in a real network due to its bandwidth constraints. In contrast, longest chain (LC), an important family of consensus protocols, has previously only been proven secure assuming an idealized network model in which all messages are delivered within bounded delay. This model-reality mismatch is further aggravated for Proof-of-Stake (PoS) LC where the adversary can spam the network with equivocating blocks. Hence, we extend the network model to capture bandwidth constraints, under which nodes now need to choose carefully which blocks to spend their limited download budget on. To illustrate this point, we show that 'download along the longest header chain', a natural download rule for Proof-of-Work (PoW) LC, is insecure for PoS LC. We propose a simple rule 'download towards the freshest block', formalize two common heuristics 'not downloading equivocations' and 'blocklisting', and prove in a unified framework that PoS LC with any one of these download rules is secure in bandwidth-constrained networks. In experiments, we validate our claims and showcase the behavior of these download rules under attack. By composing multiple instances of a PoS LC protocol with a suitable download rule in parallel, we obtain a PoS consensus protocol that achieves a constant fraction of the network's throughput limit even under worst-case adversarial strategies.
翻译:爆炸性袭击是对共识协议的严重关切,正如最近主要链链块索拉纳(Solana)最近断电所证明的那样,爆炸性袭击是对共识协议的严重关切。它们造成网络模式的挤压和过度信息延迟,因为其带宽限制,在真实的网络中,它们造成了拥堵和过度信息延迟。相比之下,最长时间的链(LC)是协商一致协议的一个重要大家庭,而以前只是被证明是安全的,假设一个理想化的网络模式,所有信息都是在受约束的延迟情况下发送的。模型-真实性不匹配对于“LC”来说更为严重。对于“LC”是一个简单规则,对手可以用平面块来冲击网络。因此,我们扩展网络模型模型模型以捕捉带宽限制带宽的带宽限制。为了说明这一点,我们显示“LC”在最长的链条链条上下下下下下下下下下沉, 自然的下载规则对于Pos LC来说是不安全的。我们提出了一个简单规则“向最差规则 ”, 将两个最差的螺旋规则正式地“下载 ”,,甚至将“不差规则在“LC” 的网络中,我们通过一个固定的下载规则下, 的下载中,通过这些规则的下载,通过这些规则的下载,我们通过一个固定的游戏的下载, 的下载来进行一个稳定的下载,通过这些规则, 我们的下载来进行一个固定的游戏式的游戏式的游戏式的下载, 的游戏式的下载, 的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏式的游戏, 。