This paper considers combinatorial auctions among such submodular buyers. The valuations of such buyers are placed within a hierarchy of valuations that exhibit no complementarities, a hierarchy that includes also OR and XOR combinations of singleton valuations, and valuations satisfying the gross substitutes property. Those last valuations are shown to form a zero-measure subset of the submodular valuations that have positive measure. While we show that the allocation problem among submodular valuations is NP-hard, we present an efficient greedy 2-approximation algorithm for this case and generalize it to the case of limited complementarities. No such approximation algorithm exists in a setting allowing for arbitrary complementarities. Some results about strategic aspects of combinatorial auctions among players with decreasing marginal utilities are also presented.

We examine the effect of false-name bids on combinatorial auction protocols. Falsename bids are bids submitted by a single bidder using multiple identifiers such as multiple e-mail addresses. The obtained results are summarized as follows: 1) The Vickrey-Clarke-Groves (VCG) mechanism, which is strategy-proof and Pareto efficient when there exists no false-name bids, is not false-name-proof, 2) There exists no false-name-proof combinatorial auction protocol that satisfies Pareto efficiency, 3) One sufficient condition where the VCG mechanism is false-name-proof is identified, i.e., the concavity of a surplus function over bidders.

This paper introduces a new distinctive class of combinatorial auction protocols called priceoriented, rationing-free (PORF) protocols. The outline of a PORF protocol is as follows: (i) for each bidder, the price of each bundle of goods is determined independently of his/her own declaration (while it can depend on the declarations of other bidders), (ii) we allocate each bidder a bundle that maximizes his/her utility independently of the allocations of other bidders (i.e., rationing-free). Although a PORF protocol appears quite different from traditional protocol descriptions, surprisingly, it is a sufficient and necessary condition for a protocol to be strategy-proof. Furthermore, we show that a PORF protocol satisfying additional conditions is false-name-proof; at the same time, any falsename-proof protocol can be described as a PORF protocol that satisfies the additional conditions. A PORF protocol is an innovative characterization of strategy-proof protocols and the first attempt to characterize false-name-proof protocols. Such a characterization is not only theoretically significant but also useful in practice, since it can serve as a guideline for developing new strategy/false-name proof protocols. We present a new false-nameproof protocol based on the concept of a PORF protocol. 1

This paper presents a secure dynamic programming protocol that utilizes homomorphic encryption. By using this method, multiple agents can solve a combinatorial optimization problem among them without leaking their private information. More specifically, in this method, multiple servers cooperatively perform dynamic programming procedures for solving a combinatorial optimization problem by using the private information sent from agents as inputs. Although the severs can compute the optimal solution correctly, the inputs are kept secret even from the servers.

Motivated by the rise of online auctions and their relative lack of security, this paper analyzes two forms of cheating in sealed-bid auctions. The first type of cheating we consider occurs when the seller spies on the bids of a second-price auction and then inserts a fake bid in order to increase the payment of the winning bidder. In the second type, a bidder cheats in a first-price auction by examining the competing bids before deciding on his own bid. In both cases, we derive equilibrium strategies when bidders are aware of the possibility of cheating. These results provide insights into sealedbid auctions even in the absence of cheating, including some counterintuitive results on the e#ects of overbidding in a first-price auction.

Intuitively, one might expect that a seller’s revenue from an auction weakly increases as the number of bidders grows, as this increases competition. However, it is known that for combinatorial auctions that use the VCG mechanism, a seller can sometimes increase revenue by dropping bidders. In this paper we investigate the extent to which this problem can occur under other dominant-strategy combinatorial auction mechanisms. Our main result is that such failures of “revenue monotonicity ” are not limited to mechanisms that achieve efficient allocations. Instead, they can occur under any dominant-strategy direct mechanism that sets prices using critical values, and that always chooses an allocation that cannot be augmented to make some bidder better off, while making none worse off.

The Internet’s computational power and flexibility have made auctions a widespread and integral part of both consumer and business markets. Though online auctions are a multibillion dollar annual activity, with a growing variety of sophisticated trading mechanisms, scientific research on them is at an early stage. This paper analyzes the current state of management science research on online auctions. It develops a broad research agenda for issues such as the behavior of online auction participants, the optimal design of online auctions, the integration of auctions into the ongoing operation of firms, and the use of the data generated by online auctions to inform future trading mechanisms. These research areas will draw from applied and theoretical work spanning management science, economics, and information systems. (Auctions; Internet) 1.

In open, anonymous environments such as the Internet, mechanism design must be extended to take new types of manipulation into account—especially, the possibility that an agent participates in the mechanism multiple times. General social choice or voting settings lie at the heart of mechanism design and provide a natural starting point. A (randomized, anonymous) voting rule maps any multiset of total orders of (aka. votes over) a fixed set of alternatives to a probability distribution over these alternatives. A voting rule f is neutral if it treats all alternatives symmetrically. It satisfies participation if no voter ever benefits from not casting her vote. It is false-name-proof if no voter ever benefits from casting additional (potentially different) votes. It is anonymity-proof if it satisfies participation and it is false-name-proof. We show that the class of anonymity-proof neutral voting rules consists exactly of the rules of the following form.

Auctions are a basic tool for resource allocation in non-cooperative environments. Much work in computer science, and in artificial intelligence in particular, has been concerned with algorithms for winner determination in auctions in order to maximize a designer's revenue.

Combinatorial auctions have recently attracted the interests of many researchers due to their promising applications such as the spectrum auctions recently held by the FCC. In a combinatorial auction, multiple items with interdependent values are sold simultaneously and bidders are allowed to bid on any combination of items. This paper presents a method for implementing several secure combinatorial auction protocols based on our newly developed secure dynamic programming protocol.