Portable reputation: Proving ownership of reputations across portals

User reputation has become a valuable commodity for enabling trusted transactions on the Internet especially with strangers in virtual communities. However, the reputation information about the various users are normally locked-up in the silos of different web-portals where the members interact. This effectively creates multiple reputation ratings for the same user, each one painstakingly built over a long time at each web-portal. Though this status quo is favorable for established webportals as it enables them to lock-in their customers, consumers have a strong interest in a portable reputation system that allows them to cross the boundaries of the competing portals. In this paper, we present a portable reputation mechanism which is managed by the users on their own with minimal co-operation from the web-portals. This method enables a user to combine from various portals the reputation information of others, which are proven to belong to them in a reliable and cryptographically secure way. Users can appropriately weigh the reputation from different web-portals according to their individual choice and trust in the different web-portals. The solution has the advantage that it does not require any unified reputation rating framework implemented by all web-portals. Additionally the cryptographic binding is constructed such that it prevents users to form a coalition and share their good reputation ratings among them.