Privacy-respecting Reputation System for Future Internet Communities

Internet (or online) communities gain more and more significance in the life of many people who do not have enough time or the opportunity to share their interests with people having the same interests in the real world. The term ”virtual community” or ”online community” was introduced by Howard Rheingold [5] already 1993. At this time communities still often were formed by only a small number of people knowing each other quite well. Nowadays the picture of communities is different: With more and more people using the Internet more and more people become members of Internet Communities and the number of communities is growing. People with the same interests spread all over the world meet each other in Internet communities. But when interacting with strangers security requirements and trust issues become important. An interactor wants to know what to expect from his interactors and wants to assure the others’ trustworthiness. The trustworthiness refers to the fact that users have certain expectations on the interactors’ behaviour that these might fulfil or not. Users who fulfil these expectations are seen as trustworthy in the future while those who do not are not trustworthy. Most users adapt their behaviour in future interactions to the trustworthiness of the interactors in former interactions. To help new interactors to estimate the others’ behaviour and to motivate interactors to fulfil the others expectations reputation systems have been designed and established that collect the experiences former interactors made. These experiences only can give a clue how others might interact in the future because e.g., interactors have different various expectations, former interactors may have lied about others’ behaviour [1], users may simply fail to fulfil expectations or may suddenly change their behaviour. But despite these uncertainties a usually large number of reputations and an honest majority of former interactors will hopefully reach that misbehaviour in future interactions occurs only rarely. A very-popular example of a reputation system is implemented by eBay, since 1995 a provider of an electronic marketplace: It offers users registered with eBay to sell and buy arbitrary items to each other. The exchange of item and money to be paid for the item between two users usually is done by bank transfer and conventional mail. Many of these exchanges are successful, but unfortunately some are not. For this reason in 1996 a reputation system was introduced to collect the experiences sellers and buyers made with these exchanges. After every exchange buyers and seller may give comments or/and marks to each other