1. Criticality Aware Access Control Model for Pervasive Applications Sandeep K. S. Gupta, T. Mukherjee, K. Venkatasubramanian Impact Lab (http://impact.asu.edu) Department of Computer Science & Engineering Ira A. Fulton School of Engineering Arizona State University Tempe, Arizona, USA Supported in part by Mediserve Inc and US National Science Foundation

2. Overview Motivation Critical Events, Criticality Criticality Aware Access Control (CAAC) Challenges Architecture Specification Verification Conclusions and Future Work

3. Access Control in Smart Spaces Smart spaces – e.g. homes, hospitals – allow inhabitants to physically interact with information-rich virtual entities. Access control necessary to prevent unauthorized access for malicious use. How to balance access Flexibility and Security?  Stringent access control may prevent expedited mitigative actions in case of emergencies  Relaxing access control may invite malicious use Traditional access control models (mechanisms + policies) are not suitable  Mainly reactive and not designed to handle emergency (critical) scenarios. Goal: To design a smart-space access control model that provides necessary flexibility for handling access control in case of emergencies while minimizing security risks.

4. Critical events Events which cannot be responded to, using the routine set of capabilities of the subjects. Examples:  Tornado is a critical event for a smart-home.  Heart-attack is a critical event in a home environment. Critical Events Mitigation Emergency Situation Normal Situation Emergency policy Routine policy

5. Characteristics of Critical Events Requires exceptional set of actions for controlling the emergency – avoiding catastrophic failure. Request based reactive context evaluation is inadequate. Proactive context monitoring is required. We define the term ‘Criticality’ as  the measure of responsiveness required for an emergency situation Normal actions Critical event Exceptional actions

6. Temporal Requirement for Criticality Every critical event has a Window of opportunity (W o ) to respond. Value of W o is criticality dependent. WoWo Critical Event Mitigation Time Normal actions Mitigative actions

7. Examples of Criticality and W o Heart attack - 1st one hour critical (golden hour). Tornado – evacuation within 5 minutes of first warning. * Data-center - 90 seconds after cooling failure. Disaster Recovery – 30 days time. ** *http://www.fema.gov/pdf/rrr/ndis_rev_oct27.pdf**http://www.fema.gov/pdf/library/fema_apa_ch4.pdf

8. Goals of Criticality Aware Access Control Facilitate timely mitigation of criticality  May require change in access privileges  Proactive – automatic and continuous context evaluation  Duration of change in access privileges should be finite.  If critical emergency, choose users provide access Traditional access control is inadequate  Reactive – explicit request-based context evaluation  If ok, provides access

9. Criticality Aware Access Control (CAAC) CAAC Allow another doctor to Access Patient Data Treat Patient Patient Emergency (Doctor not available ) CAAP mode Patient (No Emergency) Normal mode In this mode, an alternate set of access privileges are enforced for facilitating mitigative actions

10. CAAC Challenges / Properties Responsiveness  How fast to react ? Correctness  How to evaluate context / detect criticality? Liveness  How long to impose CAAP-mode? Non-Repudiability  How to deter malicious behavior as a result of privilege changes in CAAP-mode?

11. Responsiveness Measures the speed with which the alternate set of policies is enforced after the occurrence of a critical event. If,  T a is the time to take mitigative actions for a critical event  D is the time to initiate the enforcement. Then,  The Critical Event can be successfully handled iff D + T a ≤ W o

12. Liveness The duration of policy changes (T CAAP ), in response to critical events, should be:  Finite  Lasts only as long as needed If,  T EOC is the time instant when a criticality is controlled.  T EU is the time instant when all the necessary mitigative steps for a criticality have been taken. Then, assuming criticality occurred at time 0, T CAAP = min (T EOC, T EU, W o )

13. Correctness and Non-Repudiability Correctness  CAAP-mode should only be initiated in response to a critical event.  Highly system dependent. Non-Repudiability  All system activities performed in the CAAP-mode, should be monitored for ensuring accountability.  Deters malicious use of system during criticality, when alternate (possibly elevated) privileges are in place.

14. CAAC Architecture Extends Context Aware Role Based Access Control (CA-RBAC) by introducing CMU. CA-RBAC is an event with W o = infinity Proactive context evaluation as opposed to reactive in CA-RBAC.

15. Criticality Management Unit (CMU) Proactively monitors for the context and intelligently detects the occurrence of a critical event Determines the level of criticality and the associated W o based on the input from CI Moves the system into CAAP-mode and informs other components in the architecture about this Provides the access control meta-data to the CNU for determining the policies for the CAAP-mode Queries specific context information during normal mode (as in CA-RBAC)

16. CAAC – Big Picture WoWo Critical Event T EOC Time Normal mode CAAP-mode WoWo Critical Event Time Scenario 1 Scenario 2 CAAP is reverted after W o expires CAAP is reverted when the criticality is mitigated

17. Domain of CAAC Criticality Aware Access Control (Proactive) Role Based Access Control CA-RBAC (Reactive) CAAC Context Aware Access Control (Reactive) Criticality Aware Access Control (non-role based)

18. CAAC Model Access to resources provided based on:  Criticality  Other contexts Privileges given to subjects implemented using Role Based Access Control (RBAC) model. Two types of roles:  System Role (r sys ) : role assigned when subject joins the system, doctor in hospital.  Space Role (r space ) : role assigned based on subject’s domain of work, surgeon in ED.

19. CAAC Model (Contd..) Each resource maintains a list of roles and associated privileges called Access Control List (ACL). The function f maps the users’ space roles onto a corresponding role in the ACL. The presence of criticality leads to the mapping of the users’ space role to a different one in the ACL. Our sample specification, always promotes the users’ roles in the event of criticality.  Promoted Role Table (PRT) is maintained for accountability Space Role Role 1 Role 2 Role N Privileges for Role 1 Privileges for Role 2 Privileges for Role N f Criticality Detection Role Privileges ACL

20. CAAC- Policy Specifications Specify rules for accessing service provided by resource. Two types of policies:  Administrative Define the rules for administrative function within the system.  Access Control Define the rules based on which access is given to subjects for both critical and non-critical situations.

21. Access Control Specification Promote Role – elevates subject’s privileges when criticality is detected (system goes into CAAP-mode) Demote Role – resets subject’s privileges when criticality is mitigated (or Wo is expired). Notify Critical  proactively monitors for critical events  determines the appropriate elevation/reset of subject’s privileges using promoterole function. Access Control Predicate (ACP)  Boolean condition that determines the access to resources when explicit access requests are made.

22. Promote Role Step 1: Determine the occurrence of Criticality Step 2: If one found  Determine W o  Compute new Space Role with elevated privileges.  Update PRT. Step 3: Return the new space role

23. Demote Role Step 1: For each resource reset the role of users back to their original space role. Step 2: Update PRT accordingly.

24. Notify Critical Continuously monitor system for occurrence of criticality  If no criticality found AND system is in CAAP-mode (T EOC ) Demote role Revert system to normal state  If criticality found AND system is in CAAP-mode, BUT W o expired  Demote role  Revert system to normal state All mitigate steps have been taken (T EU )  Demote role  Revert system to normal state  If criticality found AND system is not in CAAP-mode Set system to CAAP-mode Find and notify appropriate users Promote their roles.

25. Access Control Predicate Previous specifications catered for:  Proactive context monitoring  Automatic policy changes ACP is used for providing access on explicit request from users, based on  Current context  Validity of the request  Availability of required services

26. Administrative Policies Adding and removing Space Roles. Adding and removing System Roles. Role Accountability  examines activities during the period when subject’s privileges are elevated.  checks the PRT.

27. Putting it all together Notify Critical Promote Role Demote Role ACP Role Accountability

28. Verification of the specification Correctness: The system can enter the CAAP-mode iff there is a critical event (ensured by Notify Critical). Liveness: For a single critical event, a subject’s role is promoted for a maximum of W o time (ensured by Notify Critical). Responsiveness: When a critical event occurs:  The subject is immediately notified (using Notify Critical)  If required the subject’s access privileges are elevated (role promotion using Promote Role)  Any role promotion is active until either the criticality is controlled or it cannot be controlled anymore (this is ensured by Notify Critical and Demote Role). Non-repudiation: Malicious use of elevated privileges after the occurrence of a critical event is non-repudiable (ensured by Role Accountability).

29. Conclusions Criticality Aware Access Control Proactive context monitoring Ideal for emergency management Automated and flexible Push based access Traditional Access Control Reactive context monitoring Slower for emergency management Manual and inflexible Pull based access

30. Future Work Studying the interdependencies among the different properties of CAAC  e.g. how does fast response affects mitigation capability? Studying multiple simultaneous criticalities  What policies to enforce in the CAAP mode?  How to model the resulting emergency situation?  What are the conditions for mitigation of all the criticalities?

31. Reference F. Adelstein, S. K. S. Gupta, G. G. Richard and L. Schwiebert, “Fundamentals of Mobile and Pervasive Computing'‘, McGraw Hill, 2005 R. Sandhu, E. Coyne, H. Feinstein and C. Youman, ``Role Based Access Control Models'‘, In IEEE Computer, Feb, 1996.pp 38-47 A. Kumar, N. Karnik and G. Chafle, ``Context Sensitivity in Role- based Access Control'‘, In ACM SIGOPS OS Review 36(3), July, 2002 Working Group on Natural Disaster Information Systems, ``Effective Disaster Warning'‘, November, 2000 G. Sampemane, P. Naldurg and R. Campbell, ``Access control for Active Spaces'‘, In Proc. of ACSAC, 2002