During the past decade, online collaboration has grown from a practice primarily associated with the workplace to a social phenomenon, where ordinary people share information about their life, hobbies, interests, politics etc. In particular, social software, such as open collaborative authoring systems like wikis, has become increasingly popular. This is probably best illustrated through the immense popularity of the Wikipedia, which is a free encyclopedia collaboratively edited by thousands of Internet users with a minimum of administration.
As more and more people come to rely on the information stored in open collaborative authoring systems, security is becoming an important concern for such systems. Inaccuracies in the Wikipedia have been rumoured to cause students to fail courses, innocent people have been associated with the murder of John F. Kennedy, etc. Improving the correctness, completeness and integrity of information in collaboratively authored documents is therefore of vital importance to the continued success of such systems.
It has previously been observed that integrity is the most important security property in open collaborative authoring systems. In this paper we propose a general security model for open collaborative authoring systems based on a combination of classic integrity mechanisms from computer security and reputation systems. The model is able to accommodate a number of different integrity policies and three different policies are presented in the paper. While the model provides a reputation based assessment of the trustworthiness of the information contained in a document, the primary objective is to prevent untrustworthy authors from compromising the integrity of the document. In order to determine the effectiveness of the proposed integrity model, we present an attacker model for open collaborative authoring systems, which allows us to calculate the vulnerability of a given document based on the fraction of malicious authors in the system.