  Interconnected autonomous systems often share security risks. However, an
autonomous system lacks the incentive to make (sufficient) security investments
if the cost exceeds its own benefit even though doing that would be socially
beneficial. In this paper, we develop a systematic and rigorous framework for
analyzing and significantly improving the mutual security of a collection of
ASs that interact frequently over a long period of time. Using this framework,
we show that simple incentive schemes based on rating systems can be designed
to encourage the autonomous systems' security investments, thereby
significantly improving their mutual security.
