A Context-Aware Model of Trust for Facilitating Secure Ad Hoc Collaborations

Ad hoc collaborations often necessitate impromptu sharing of sensitive information or resources between member organizations. Each member of resulting collaboration needs to carefully assess and tradeoff the requirements of protecting its own sensitive information against the requirements of sharing some or all of them. The challenge is that no policies have been previously arrived at for such secure sharing (since the collaboration has been formed in an ad hoc manner). Thus, it needs to be done based on an evaluation of the trustworthiness of the recipient of the information or resources. In this chapter, the authors discuss some previously proposed trust models to determine if they can be effectively used to compute trustworthiness for such sharing purposes in ad hoc collaborations. Unfortunately, none of these models appear to be completely satisfactory. Almost all of them fail to satisfy one or more of the following requirements: (i) well defined techniques and procedures to evaluate and/or measure trust relationships, (ii) techniques to compare and compose trust values which are needed in the formation of collaborations, and (iii) techniques to evaluate trust in the face of incomplete information. This prompts the authors to propose a new vector (we use the term “vector” loosely; vector in this work means a tuple) model of trust that is suitable for reasoning about the trustworthiness of systems built from the integration of multiple subsystems, such as ad hoc collaborations. They identify three parameters on which trust depends and formulate how to evaluate trust relationships. The trust relationship between a truster and a trustee is associated with a context and depends on the experience, knowledge, and recommendation that the truster has with respect to the trustee in the given context. The authors show how their model can measure trust in a given context. Sometimes enough information is not available about a given context to calculate the trust value. Towards this end the authors show how the relationships between different contexts can be captured using a context graph. Formalizing the relationships between contexts allows us to extrapolate values from related contexts to approximate a trust value of an entity even when all the information needed to calculate the trust value is not available. Finally, the authors develop formalisms to compare two trust relationships and to compose two or more of the same – features that are invaluable in ad hoc collaborations.