Poster: arbitrators in the security infrastructure, supporting positive anonymity.

Traditional public key infrastructure is an example for basing the security of communication among users and servers on trusting a Certificate Authority (CA) which is a Trusted Authority (TA). A traditional, centralized CA or TA should only be involved in a setup stage for communication, or risk causing a bottleneck. Peer to peer assistance may replace the CA during the actual communication transactions. We introduce such assistants that we call arbitrators. Arbitrators are semi-trusted entities that facilitate communication or business transactions. The communicating parties, users and servers, agree before a communication transaction on a set of arbitrators that they trust (reputation systems may support their choice). Then, the arbitrators receive
resources, e.g. a deposit, and a service level agreement between participants such that the resources of a participant are returned if and only if the participant acts according to the agreement.
We demonstrate the usage of arbitrators in the scope of conditional (positive) anonymity. A user may interact anonymously with a server as long as the terms for anonymous communication are honored. In case the server finds a violation of the terms, the server proves to the arbitrators that a violation took place and the arbitrators publish the identity of the user. Since the arbitrators may be corrupted, the scheme ensures that only a large enough set of arbitrators may reveal user’s identity, which is the deposited resource in the case of conditional anonymity.