Finding trusted publish/subscribe trees

Publish/Subscribe systems assume that clients and brokers abide by the matching and forwarding protocols. Such an assumption implies implicit trust between all components of the system and has led to security issues being largely ignored. As publish/subscribe is increasingly used in applications where implicit trust can not be assumed, an approach is required to mitigate misbehaviour. We propose the construction and reconfiguration of the event forwarding topology, the publish/subscribe tree (PST), with respect to the trust requirements of the clients. The principal contribution of this paper is a trust metric for PSTs, which aggregates each client’s trust evaluation of a PST to give a socially acceptable trust evaluation and allows for the ordering of PSTs. Additionally, we define the PST trust maximisation problem with overhead budget, which is solved by the PST that maximises trust within an overhead budget for a given advertisement. A tabu search based algorithm for this problem is presented and is shown to scale to large problem instances and give good approximations of the optimal solutions.