Abstract: Quality of protection can be seen as the security target of security modules when doing their security treatments,which can be judged by ctuantitative criteria. The question of how to evaluate whether the current software system has fulfills the quality of protection target objectively and effectively has become one of the hotspots of research.Currently, however, most security professionals use the ctualitative method for security evaluation, which is highly sub- jective and makes the evaluation result dependent on the individual experience and thus unreliable. So what needed are substantive and quantitative security metrics. Because of the complexity and the difficulty of implementing the security metrics, a novel security evaluation model was presented in this paper, which analyzed the relative security level of given systems from the views of attack surface, denial of service and attack graph. At last, a general discussion for the process and the result of the evaluation were given.

Key words: Quality of protection, Security metrics, Attack surface, Denial of service, Vulnerability, Attack graph