Today, many auctions are carried out with the help of intermediary platforms like Google and eBay. We refer to such auctions as platform-assisted auctions.Traditionally, the auction theory literature mainly focuses on designing auctions that incentivize the buyers to bid truthfully,assuming that the platform always faithfully implements the auction. In practice, however, the platforms have been found to manipulate the auctions to earn more profit, resulting in high-profile anti-trust lawsuits. We propose a new model for studying platform-assisted auctions in the permissionless setting. We explore whether it is possible to design a dream auction in thisnew model, such that honest behavior is the utility-maximizing strategy for each individual buyer, the platform, the seller, as well as platform-seller or platform-buyer coalitions.Through a collection of feasibility and infeasibility results,we carefully characterize the mathematical landscape of platform-assisted auctions. We show how cryptography can lend to the design of an efficient platform-assisted auction with dream properties. Although a line of works have also used MPC or the blockchain to remove the reliance on a trusted auctioneer, our work is distinct in nature in several dimensions.First, we initiate a systematic exploration of the game theoretic implications when the service providers are strategic and can collude with sellers or buyers. Second, we observe that the full simulation paradigm is too stringent and leads to high asymptotical costs. Specifically, because every player has a different private outcomein an auction protocol, running any generic MPC protocol among the players would incur at least $n^2$ total cost. We propose a new notion of simulation calledutility-dominated emulation.Under this new notion, we showhow to design efficient auction protocols with quasilinear efficiency.

翻译：如今，许多拍卖活动在谷歌和eBay等中介平台的协助下进行。我们将此类拍卖称为平台辅助拍卖。传统上，拍卖理论研究主要聚焦于设计激励买家诚实出价的拍卖机制，其前提假设是平台始终忠实地执行拍卖规则。然而实践中发现，平台会通过操纵拍卖来获取更高利润，这已引发多起备受关注的反垄断诉讼。本文提出一个用于研究无许可环境下平台辅助拍卖的新模型。我们探讨在该新模型中能否设计出具有理想属性的拍卖机制，使得诚实行为成为每个独立买家、平台、卖家以及平台-卖家或平台-买家联盟的效用最大化策略。通过一系列可行性与不可行性结果，我们系统刻画了平台辅助拍卖的数学理论图景。我们展示了密码学技术如何助力设计具备理想属性的高效平台辅助拍卖机制。尽管已有系列研究采用多方计算或区块链技术以消除对可信拍卖方的依赖，但本文研究在多个维度具有本质区别：首先，我们开创性地系统探究了服务提供商具有策略性且可与卖家或买家合谋时的博弈论影响；其次，我们发现完全模拟范式过于严苛且会导致较高的渐近成本。具体而言，由于拍卖协议中每个参与者都拥有不同的私有输出，在参与者间运行任何通用多方计算协议将产生至少$n^2$的总成本。我们提出称为效用支配仿真的新模拟概念，并在此新概念下展示了如何设计具有拟线性效率的高效拍卖协议。