Cryptographic Protocols for Secure Second-Price Auctions

In recent years auctions have become more and more important in the field of multiagent systems as useful mechanisms for resource allocation, task assignment and last but not least electronic commerce. In many cases the Vickrey (second-price sealed-bid) auction is used as a protocol that prescribes how the individual agents have to interact in order to come to an agreement. The main reasons for choosing the Vickrey auction are the existence of a dominant strategy equilibrium, the low bandwidth and time consumption due to just one round of bidding and the (theoretical) privacy of bids. This paper specifies properties that are needed to ensure the accurate and secret execution of Vickrey auctions and provides a classification of different forms of collusion. We approach the two major security concerns of the Vickrey auction: the vulnerability to a lying auctioneer and the reluctance of bidders to reveal their private valuations. We then propose a novel technique that allows to securely perform second-price auctions

Asynchronous Computational VSS with Reduced Communication Complexity

Verifiable secret sharing (VSS) is a vital primitive in secure distributed computing. It allows an untrusted dealer to verifiably share a secret among n parties in the presence of an adversary controlling at most t of them. VSS in the synchronous communication model has received tremendous attention in the cryptographic research community. Nevertheless, recent interest in deploying secure distributed computing over the Internet requires going beyond the synchronous communication model and thoroughly investigating VSS in the asynchronous communication model. In this work, we consider the communication complexity of asynchronous VSS in the computational setting for the optimal resilience of n = 3t + 1. The best known asynchronous VSS protocol by Cachin et al. has O(n 2) message complexity and O(κn 3) communication complexity, where κ is a security parameter corresponding to the size of the secret. We close the linear complexity gap between these two measures for asynchronous VSS by presenting two protocols with O(n 2) message complexity and O(κn 2) communication complexity. Our first protocol satisfies the standard VSS definition, and can be used in stand-alone VSS scenarios as well as in applications such as Byzantine agreement. Our second and more intricate protocol satisfies a stronger VSS definition, and is useful in all VSS applications including multiparty computation and threshold cryptography