Abstract Ad exchanges are kind of the most popular online advertising marketplaces for trading ad spaces over the Internet. Ad exchanges run auctions to sell diverse ad spaces on the publishers’ web-pages to advertisers, who want to display ads on ad spaces. However, the parties in an ad auction cannot verify whether the auction is carried out correctly or not. Furthermore, the advertisers are usually unwilling to reveal their sensitive bids and identities. In this paper, we jointly consider the auction verifiability and the advertisers’ privacy preservation, and thus propose ERA, which is an E fficient, p R ivacy-preserving, and verifi A ble online auction mechanism for ad exchanges. ERA exploits an order preserving encryption scheme to guarantee privacy preservation, and achieves verifiability by constructing a novel protocol of privacy preserving integer comparison, which is built on the Paillier homomorphic encryption scheme. We extensively evaluate the performance of ERA, and our evaluation results show that ERA satisfies several desirable properties with low computation, communication, and storage overheads, so ERA can be easily deployed in today's ad exchanges.
Sealed-Bid auction is an efficient and rational way to establish the price and trading goods in the open market. However sealed-bid auctions are subject to bid-rigging attack. Receipt-free mechanisms are proposed to prevent bid-rigging. So far, all the proposed receipt-free mechanisms are based on strict assumptions: i The channel between bidders and the auction authorities like auctioneer, sealer, registering authority etc. must be untappable, 2 the authorities are assumed to be honest not colluded, hence ensure privacy and anonymity of bids. Moreover, the existing receipt-free mechanisms are bandwidth intensive estimated difference between the minimum and maximum bidding price. In this paper, we present a receipt-free sealed-bid auction mechanism which can withstand public channel and colluded authorities. The proposed mechanism can work even under the situation where all the authorities except one are colluded. Unlike the existing mechanisms, the computational complexity of the proposed mechanism is independent of the bandwidth and only depends on the number of valid bids. The auction mechanism requires Omlogm computational steps to resolve the winner, where m is the number of valid bids in the system. Copyright © 2015 John Wiley & Sons, Ltd.   We argue that threshold trust is not an option in most of the real-life electronic auctions. We then propose two new cryptographic Vickrey auction schemes that involve, apart from the bidders and the seller S, an auction authority A so that unless S and A collude the outcome of auctions will be correct, and moreover, S will not get any information about the bids, while A will learn bid statistics. Further extensions make it possible to decrease damage that colluding S and A can do, and to construct (m + 1)st price auction schemes. The communication complexity between the S and A in medium-size auctions is at least one order of magnitude less than in the Naor-Pinkas-Sumner scheme. Privacy has become a factor of increasing importance in auction design. We propose general techniques for cryptographic first-price and (M+1)st-price auction protocols that only yield the winners' identities and the selling price. Moreover, if desired, losing bidders learn no information at all, except that they lost. Our security model is merely based on computational intractability. In particular, our approach does not rely on trusted third parties, e.g., auctioneers. We present an efficient implementation of the proposed techniques based on El Gamal encryption whose security only relies on the intractability of the decisional Diffie—Hellman problem. The resulting protocols require just three rounds of bidder broadcasting in the random oracle model. Communication complexity is linear in the number of possible bids. We investigate whether it is possible to preserve privacy in sealed-bid auctions to a maximal extent. In particular, this paper focuses on unconditional full privacy , i.e., privacy that relies neither on trusted third parties (like auctioneers), nor on computational intractability assumptions (like the hardness of factoring). These constraints imply a scenario in which bidders exchange messages according to some predefined protocol in order to jointly determine the auction outcome without revealing any additional information. It turns out that the first-price sealed-bid auction can be emulated by an unconditionally fully private protocol. However, the protocol's round complexity is exponential in the bid size, and there is no more efficient protocol. On the other hand, we prove the impossibility of privately emulating the second-price sealed-bid auction for more than two bidders. This impossibility holds even when relaxing various privacy constraints such as allowing the revelation of all but one losing bid (while maintaining anonymity) or allowing the revelation of the second highest bidder's identity.