Similarity Measure for Security Policies in Service Provider Selection

Abstract

The interaction between different applications and services requires expressing their security properties. This is typically defined as security policies, which aim at specifying the diverse privileges of different actors. Today similarity measure for comparing security policies becomes a crucial technique in a variety of scenarios, such as finding the cloud service providers which satisfy client’s security concerns. Existing approaches cover from semantic to numerical dimensions and the main work focuses mainly on XACML policies. However, few efforts have been made to extend the measure approach to multiple policy models and apply it to concrete scenarios. In this paper, we propose a generic and light-weight method to compare and evaluate security policies belonging to different models. Our technique enables client to quickly locate service providers with potentially similar policies. Comparing with other works, our approach takes policy elements’ logic relationships into account and the experiment and implementation demonstrate the efficiency and accuracy of our approach.

Appendices

Appendix

A Brute-force based test for existing work

Figure 10 shows the brute-force test result of policy similarity score by using the same test environment illustrated in Sect. 4. The y-axis represents the PSM score computed by the algorithm proposed in [10]; the x-axis shows the test result of policy similarity defined by Eq. (7) [10], where Sreq denotes the set of the requests with the same decisions from $p_1$ and $p_2$ and Req is the set of the requests applicable to either $p_1$ or $p_2$:

$$\begin{aligned} \begin{aligned} S_{policy}(p_1,p_2)={|Sreq|}/{|Req|} \end{aligned} \end{aligned}$$

(7)

We remark that the similarity score computed does not approximate to the test result. The main reason is that, firstly, as a brute-force based test method, our input requests are more exhaustive than ones generated by other test tools such as MTBDD [18]. Secondly, the PSM algorithm defined in [10] focuses only on the literal level but not logic aspect of security policy. As a result, two security rules sharing the majority of common elements are considered to hold a higher similarity score. However, the rest of elements may cause totally different decisions which indicates that the two rules are not similar in terms of output.

Fig. 10.

Experiment of similarity score (set-4).