Traditional security model, where the identity of all possible requesting subjects must be pre-registered in advance, is not suitable for the distributed applications with strong real-time requirements. A promising approach is represented by automated trust negotiation, which establishes trust between strangers through the exchange of digital credentials and the use of access control policies. As the credentials contain sensitive information, entities disclose credentials circumspectly. Given multiple credential exchange sequences achieving the same result, it is desirable to pick the sequence that discloses a set of minimum sensitive credentials. In this paper, we model the policies participating trust negotiation as a Negotiation Petri Net and propose a trust negotiation MSC strategy, which works by the characteristics of Negotiation Petri Net architecture, the behaviors of auto trust negotiation and the greedy algorithm. We prove that the MSC strategy is complete, efficient and mini-sensitivity cost. It also makes sure that no irrelevant credentials will be disclosed during negotiations.
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