发表机构
University of Michigan; Sun Yat-sen University; Adrasteia Labs（密歇根大学; 中山大学; 阿斯特赖亚实验室）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
针对Uniswap v2类自动做市商，精确推导出私有内存池中交易规模泄漏对三明治攻击盈利的影响阈值，并证明最小一致规模决定最优前跑策略及拍卖均衡结果。
AI 中文摘要
私有和加密的内存池隐藏待处理交易，以阻止三明治攻击和其他形式的最大可提取价值（MEV），但它们所隐藏的很少是全部信息：交易对、方向以及交易规模的粗略范围仍可能泄漏。多少泄漏会使三明治攻击有利可图？我们针对一个免手续费的恒定乘积自动做市商（即Uniswap v2背后的定价规则）给出了精确答案。交易者观察到包含受害者规模的区间，并在第一价格拍卖中出价以获得对其执行三明治攻击的权利，而获胜的前跑者必须确保受害者的交易在区间内的每个规模下都可执行。答案取决于与泄漏一致的最小规模。该最小规模单独决定了可行的前跑策略，最大的可行前跑策略在逐点、期望和最坏情况利润下均最优，且保证利润具有闭式解。当执行有成本时，希望排除在所有一致规模下均有利可图的三明治攻击的隐私层，因此可以揭示关于规模的任何信息，除非揭示高于明确阈值的下界；区间的上端无关紧要。当有两个或更多对称交易者时，拍卖的每个纯策略完美贝叶斯均衡都将全部预期净租金交给拍卖者。如果方向也被隐藏，则没有非或有首腿前跑可以同时前跑两个可能方向，而交易后套利即使在完美的交易前隐藏下也能存活。
英文摘要
Private and encrypted mempools hide pending transactions to stop sandwich attacks and other forms of maximal extractable value (MEV), but what they hide is rarely everything: a transaction's pair, direction, and a coarse range for its size can still leak. How much leakage makes sandwiching pay? We answer exactly for a fee-free constant-product automated market maker, the pricing rule behind Uniswap v2. Traders observe an interval containing the victim's size and bid in a first-price auction for the right to sandwich it, and the winning front-run must keep the victim's trade executable at every size in the interval. The answer turns on the smallest size consistent with the leak. It alone determines the feasible front-runs, the largest feasible front-run is optimal for pointwise, expected, and worst-case profit alike, and the guaranteed profit has a closed form. When execution is costly, a privacy layer that wants to rule out sandwiches profitable at every consistent size may therefore reveal anything about the size except a lower bound above an explicit threshold; the upper end of the range is irrelevant. With two or more symmetric traders, every pure-strategy perfect Bayesian equilibrium of the auction hands the entire expected net rent to the auctioneer. If the direction is hidden too, no non-contingent first leg front-runs both possible directions, while post-trade arbitrage can survive even perfect pre-trade hiding.
Comments23 pages, 1 figure, 1 table. Accepted to NeurIPS 2026
