This paper studies collusion in repeated auctions when bidders communicate prior to each stage auction. The paper presents a folk theorem for independent and correlated private signals and general interdependent values. Specifically, it identifies conditions under which an equilibrium collusion scheme is fully efficient in the sense that the bidders’ payoff is close to what they get when the ob...

At ISC 2012, Bender et al. introduced the notion of domainspecific pseudonymous signatures for ID documents. With this primitive, a user can sign with domain-specific pseudonyms, that cannot be linked across domains but that are linkable in a given domain. However, their security model assumes non-collusion of malicious users, which is a strong assumption. We therefore propose improvements to t...