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Towards Modelling Information Security with Key-Challenge Petri Nets

Towards Modelling Information Security with Key-Challenge Petri Nets. Teijo Venäläinen teijo.v.o.venalainen@jyu.fi. Contents. Introduction Various modelling methods Graph based modelling Key-Challenge Petri Nets. Introduction.

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Towards Modelling Information Security with Key-Challenge Petri Nets

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  1. Towards Modelling Information Security with Key-Challenge Petri Nets Teijo Venäläinen teijo.v.o.venalainen@jyu.fi

  2. Contents • Introduction • Various modelling methods • Graph based modelling • Key-Challenge Petri Nets

  3. Introduction • Since 7/2006 in Information Technology Research Institute (ITRI), Agora, JYU • Doctoral studies since 2009 • Goal is to find a method for measuring information security (IS) • Modelling and Simulation (M&S)

  4. Motivation for testing/modelling • Testing a system in use is not a feasible option => damage • Real system must be replicated (modelled) somehow • Testing is done with the modelled system • How accurately does the model represent the real system?

  5. Resulting information • For the whole system or a single component, the following results are interesting: • Mean time between failure (against attacks) • Success probability of attacks • Damage (performance degradation, money, …) • Attack route i.e. how the attack progresses • And more …

  6. Testing methods • There are different methods, where varies [1] • ”target audience” • Human involement during testing • Detail level • Role playing, ”Packet wars”, network design tools • Mathematical modelling, state machines, graph based modelling

  7. Role playing • Scenario-based training exercises • High abstraction level • Test the strategic decision making process of personnel and organizations • Computers not necessary, ”pencil & paper” • Target audience: high level decision makers • Does not provide technical IS information

  8. ”Packet wars” • Real network with real users, a dedicated test network in a laboratory • Two teams: attackers and defenders • Highly accurate method but costly • Target audience: IS professionals

  9. Network design tools • Accurate modelling of networks and normal activities • Attack modelling is limited => limited results • No human involvement during testing, only simulation • Target audience: IS professionals, network designers

  10. Mathematical modelling, state machines, graph based models • Also approximations of the real system • Provide results faster through simulation • Cheap • Easily modifyable

  11. Modelling & simulation System description Model Simulation

  12. Graph based modelling • Network attack is usually a series of interdependent actions leading to a goal (= breach in security) • Actions are illustrated using nodes and arcs => an attack graph (AG) • Assign conditions (e.g. probability) on traversing between nodes • Usually attacker’s point of view • Simulate by starting from a node and moving towards the goal node(s)

  13. Attack tree Source [2]

  14. Challenges • The system must be described at adequate level of accuracy. Scalability with large networks? • Valid input parameters (From where? How?) • Usability • Attacker’s and defender’s interaction (game theory?) • Creating graphs is labor intensive => automatic tools

  15. Petri Nets • Place (input/output): holds tokens • Arc: connects places and transitions • Transition: lets token pass through if conditions are met • Token: moves from place to place

  16. Key-Challenge Petri Nets (KCPN) • A modelling method under development • Based on Petri-nets • KCPN graph is created using network and vulnerability information • Conditions for transitions = key-challenge • challenge = security measure • key = means to circumvent/break the security measure

  17. KCPN: overview • Hierarchical i.e. modelling may be performed using various abstration levels • Modular structure • Place = network device or attack action • Arc = physical connection of devices or causal relation of attack actions • Transition = challenge (security measure)

  18. KCPN: simulation • Attacker collects keys that allow him to progress in the graph • Variables may be assigned for transitions • Probability of being detected • Duration of an attack action (time distribution) • Cost, skill level, etc. • It is possible to perform an attack action without required keys but with a greater cost/duration

  19. KCPN: results • Simulation results include: • Probability of success of an entire attack • The most vulnerable attack path • The duration of the entire attack • Results may be used as input data within the model (simulate modules independently)

  20. KCPN: example • Two hierarchy levels: • Topology level (physical world) • Attack action level (abstract world) • Multiple network devices lumped into a single node (Hosts) • Devices with similar connections, OS, software, etc. => lumped together

  21. KCPN: the physical network

  22. KCPN: the graph

  23. Sources • [1] J. Saunders. Simulation Approaches in Information Security Education. Proceedings of 6th National Colloquium for Information System Security Education, 2002. • [2] Bruce Schneier. Attack Trees. SANS Network Security 1999. http://www.cs.utk.edu/~dunigan/cns06/attacktrees.pdf

  24. Thank You!

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