Automatic XACML requests generation for policy testing

1. Automatic XACML requests generation for policy testing Antonia Bertolino, Said Daoudagh, Francesca Lonetti, Eda Marchetti Istituto di Scienza e Tecnologie dell’Informazione “A. Faedo” Consiglio Nazionale delle Ricerche

2. Agenda • Access control policies and XACML language • Why a testing methodology? • An empirical evaluation • Conclusions and future works • X-CREATE Demo

3. - - Data Resources Access Control Policies Data and resources must be protected against unauthorized, malicious or improper usage or modification Policies specification

4. Testing the Policy Implementation Policies SUT verdict request PDP request request request reply Test Suite Oracle PDP (Policy Decision Point): evaluates the requests against the access control policies

5. XACML Policy Structure Esample of Policy <Policy> <Target> <Subject>Mario Rossi</Subject> <Resource>personal id</Resource> <Action>read</Action> </Target> </Policy> Example of request <Request> <Subject>Mario Rossi</Subject> <Resource>personal id</Resource> <Action>read</Action> </Request> XACML (eXtensible Access Control Markup Language) The XACML Policy elements: • PolicySet • Policy • Target • Subjects • Resources • Actions • Environments • Rules

6. X-CREATE Testing Framework XaCml REquests derivAtion for TEsting • Implements several testing strategy: • Preliminary XPT (XML Partition Testing) • Incremental XPT • Simple Combinatorial • Hierarchical Simple • Hierarchical Incremental Instantiated Request Policies specification Request structure

7. Preliminary XPT Main Idea Deriving once and for all a universally valid generic test suite of conforming requests by applying: • A variant of the Category Partition methodology • The Boundary Conditions methodology Request structure XACML Context Schema Conforming test suite

8. E.G. Fixing ∞ to 3 X X {1,2,3} {1,2,3}

9. An Example Example of request structure <Request> <Subject> </Subject> <Subject> </Subject> <Resource> </Resource> <Action> </Action> </Request> Issue: The maximum number of structurally different intermediate requests is of 310 * 21 = 118098

10. 118098!!!! Too Much!!! Testing objectives: • New methodology for request structures generation (Incremental XPT) • New stopping criterion for test requests execution • New specific test strategysatisfying the stopping criterion (Simple Combinatorial)

11. Incremental XPT 36= 729 requeststuctures: • one value for the <AttributeValue> • zero to minOccursand maxOccurs of the ResourceContent element and those of the contained <Any> element because not used in test values generation

12. Filling request structures with values Take values from the policy under test for elements and attributes. • SubjectSet • ResourceSet • ActionSet • EnvironmentSet • An entity is a combination of 4 values taken from these sets (n-wise approach is used)

13. Toy Example <Policy> <Target> <Subject>Mario Rossi</Subject> <Resource>personal id</Resource> <Action>read</Action> </Target> </Policy>

14. Complete Table For robustness and negative testing random values for elements and attributes are added

15. How many entities? • Avoiding duplication derive all combinations of subject entities, resource entities, action entities and environment entities by applying: • the pair-wise combination (PW) • the three-wise combination (TW) • apply the four-wise combination (FW) Note: The number of combinations is limited and strictly depends on the policy considered

16. Examples Example of request <Request> <Subject>Mario Rossi</Subject> <Resource>personal id</Resource> <Action>read</Action> </Request> Example of request <Request> <Subject>Mario Rossi</Subject> <Subject>s2</Subject> <Resource>p2</Resource> <Action>read</Action> <Enviroment>e2</Enviroment> </Request> Example of request <Request> <Subject>s2</Subject> <Resource>personal id</Resource> <Action>a2</Action> </Request>

17. Simple Combinatorial Idea: derive as many requests as the possible combinations of the values of the subjects, resources, actions and environment of the XACML policy. The number of combinations could be also be used as a stopping criterion for the test case generation in XPT

18. Incremental XPT vs. Simple Combinatorial Research questions: 1st Match TSEff: adopting the proposed stopping criterion, is the fault detection of the Simple Combinatorial strategy similar to that of the Incremental XPT one? 2nd MatchTSDecr: is it possible to reduce the test suites maintaining the same level of fault detection? 3rd MatchTSIncr: is it possible to increase the Incremental XPT fault detection?

19. Rules of comparison Evaluation of the test strategies effectiveness: • Define a set of XACML policies • Apply mutation to each policy to introduce faults • Execute each set of test cases on the policy and its mutants • Establish the winner according in each match

20. Simple cobinatorial Incremental XPT XPT v.s. Simple Combinatorial 1st Match TSEff: • The same number of requests for each policy • the effectiveness of the Incremental XPT is generally higher than that of the Simple Combinatorial strategy • In two cases the fault detection of the Simple Combinatorial is higher than that of Incremental XPT

21. Deep Analysis • Incremental XPTis the winner when the access decision of the policy rules depends concurrently on the values of more than one subject or resource or action or environment entity • Simple Combinatorial is the winner when the policies are very simple and the satisfiability of the policy rules depends on the combinations of a single subject, resource, action and environment entity

22. 2nd Match TSDecr: from the first request ahead till we reached the maximum reachable percentage of fault detection Simple Combinatorial is the winner Note: For XPT usually the maximum reachable percentage is reached with almost half of the available requests =>the stopping criterion is a good upper bound

23. XPT v.s. Simple Combinatorial 3rd Match TSIncr: the loss in the fault detection effectiveness due to the stopping criterion • Execute the full pull of available requests • percentage of mutants killed could be increased a lot • Calculate the minimum # requests for the maximum fault detection effectiveness • in most of the cases the loss of fault detection effectiveness is around 15%.

24. Preliminary Conclusions and Future Works • A good fault detection percentage of the Incremental XPT testing strategy due to the variability of the structures of the generated requests • It is possible to reduce the number of requests • The high variability of the Incremental XPT strategy can limit its performance when policies are very simple • Homework: • Generalize the results • Consider further mutation operators • Conceive new test strategy generating requests containing all the possible combinations of more than one subject, resource, action and environment entity.

25. Thank you!