David Barrera, H. Güne¸s Kayacık , P.C. van Oorschot , Anil Somayaji

1. A Methodology for Empirical Analysis ofPermission-Based Security Modelsand its Application to Android Carleton University, Ottawa, ON, Canada ACM CCS(2010) David Barrera, H. Güne¸sKayacık, P.C. van Oorschot, Anil Somayaji

2. Agenda • Introduction • Access control systems • Permission-Based Security • Related Work • Android Permission Model • Self-Organizing Maps(SOM) • Result • Further Discussion&Conclusion

3. Introduction • Restrict actions on specific resources • Access control lists (ACLs) • permission-based security models • Empirical analysis • Objectives • investigate how the permission-based system in Android is used in practice • Identify the strengths and limitations of the current implementation

4. Introduction • Android uses ACLs extensively to mediate inter-process communication (IPC) and to control access to special functionality on the device • Advantages • Prevent malware • inform users what applications are capable of doing once installed • Contribution • a novel methodology for exploring and empirically analyzing permission-based models

5. Accesscontrol systems • Access control lists allows a subject to perform an action on an object only if the subject has been assigned the necessary permissions. • More sophisticated ACL-based systems allow the specification of a complex policy to control more parameters of how an object can be accessed. • Each ACL only restricts access to one action.

6. Permission-Based Security • Android requires that developers declare in a manifest a list of permissions which the user must accept prior to installing an application • Google Chrome web browseruses a permission-based architecture in its extension system • Blackberry OS enforces through signature validation thatan application has been granted permissions to access thecontrolled APIs

7. Related Work • Enck et al. describe the design and implementationof a framework to detect potentially malicious applications based on permissions requested by Android applications • Barth et al. analyzed 25 browser extensions forFirefox and identified that 78% are given more privilegesthan necessary

8. Android Permission Model • Android Market • Android applications are written in Java syntaxand each run in a custom virtual machine known asDalvik • Anythird party application can define new Functionality

9. Android Permission Model • Every application written for the Android platform must include an XML-formatted file named AndroidManifest.xml. • Permissions are enforced by Android at runtime, but must be accepted by the user at install time

11. Android Permission Model • we used the Android Asset Packaging Tool to extract the manifest and read all XML entries of type uses-permission • x = [x1, x2, …, xj ]T {0, 1}j • xj:the permission j is requested • Some error • Duplicate permission error • Request permission that do not exist

13. Self-Organizing Maps(SOM) • SOM is a type of neural network algorithm, which employs unsupervised learning • Characteristics: • SOM provides a 2-dimensional visualization of the high dimensional data • the component analysis of SOM can identify correlation between permissions.

14. Self-Organizing Maps(SOM)

15. Self-Organizing Maps(SOM)

16. Results • Effectively clustering the applications requesting similar permissions into the same neighborhood. • Winner-take-all • Applications from different categories can request similar sets of permissions

17. Results • a.p.INTERNETpermission is requested by the majority of applications in our dataset (over 60%)

18. Results • The analysis of component planes can reveal correlations between permissions • a.p.INTERNET permission fails to provide sufficiently fine-grained control of the resources • Many permissions are requested by only a few applications.

19. Further Discussion&Conclusion • Having finer-grained permissions in a permission-based system enables users to have detailed control over what actions are allowed to take place • Enhancements: • Logical permission grouping→fine-grained hierarchical permission • Logically grouping all self-defined permissions under one category • Hope that the SOM-based methodology, including visualization, is of use to others exploring independent permission-based models