Controlling Collaborative Systems -Srinivas Krishnan Dept of Computer Science UNC-Chapel Hill

Collaborative Systems Shared Resource Access Control

Requirements for Access Control Systems The access control operations must be idempotent Scalability: Need to support N-users, as well as distributed resources Preferred Goals Transparency Ease of Administration

Requirements for Access Control Systems Access Control Systems are built in layers Permissions Notifications AUDITAUDIT

Access Matrix. Access specified on a per object basis Each user is given certain permissions To scale this further Access Control Lists are used Systems that use AMs: Grove, RTCAL (central admin provides the permissions to all objects)

ACL and CCL Access Control Matrices are linked together to form ACLs for each object Capability Lists are the opposite of ACLS, where users maintain which objects they have access to. ACL CCL

Pros and Cons of ACLs Easy to implement and maintain Dynamic changing of rights hard Needs knowledge of each users needs before hand. Not always possible in a collaborative environment Also each user/object needs to be explicitly given permissions

Role Based Access Control (Sandhu et al) Permissions are assigned to roles User authenticates in a 2 step process Users Roles Request Role Permissions Resources

RBAC (cont) Notion of a session Bound to a single user accessing the resource and the roles he needs Needs a policy in place generic enough to accommodate all accesses Did not allow for migration of roles within a single session

Spatial Access Control Divides collaborative environment into spaces Collaborative Environment Collaborative Environment Space Collaborative Environment Space Collaborative Environment Space

Spatial Access Control Uses an access graph to allow for traversal between the various spaces Further we can provide constraints in movement from space to space Space A Space B Space C User1 User2

Test Setting Taking the Test CorrectionResults Professor Student Professor

Implementation Issues Order of updates and notification matter Cannot depend on a global clock to be synchronized Permissions Give Access to Bob (Op1) Remove Access to Bob (Op2)

Solution for Order of Updates Most fine-grained locking operations require “Total-Ordering” Perform Operation Check Update Counter Remote Counter > Local < Local Adopt Remote Counter X =

Fine-Grained Access Control Traditional Modes do not scale too well for N- users needing dynamic rights Fast provision of permissions Optimistic Locks and Access Control can provide native performance

Optimistic Control “Make the user ask forgiveness not permission” A similar system exists in UNIX with sudo. However, changes are permanent Resource John Everyday access John Move Resource Fire in Building Access Denied

Optimistic Access Control Needs different points of entry Resource Access Control AUDITAUDIT Normal Entry Elevated Entry

Optimistic Control Guaranteed Protection No Protection Transaction New State Compensating

Auditing Optimism Verification Classes Integrity Rules must be verified at all times Resource TransactionCompensation Verify Users

Logger Simple Optimistic Access Control File Auth Modules Transaction Checker Write to File PTPLOG Verify Log

Case-Study: P2P Collaborative Systems MOTION: Provides Access Control in a P2P environment No Centralized Access Control Scalability: N-Users N-Auth Modules Dynamic Entry & Exit of Users Role Based Access Control L1 peer & L2 peer L1 peers protect resources

Architecture

Improving Motion

Summary Access Control essential for maintaining a secure Collaborative Environment Access Control can introduce lag and degrade a user’s experience Optimistic Access Control algorithms can be used to allow user’s to experience native performance

References: Tolone, W., Ahn, G., Pai, T., and Hong, S Access control in collaborative systems. ACM Comput. Surv. 37, 1 (Mar. 2005), Povey, D Optimistic security: a new access control paradigm. In Proceedings of the 1999 Workshop on New Security Paradigms (Caledon Hills, Ontario, Canada, September , 1999). NSPW '99. ACM Press, New York, NY, Chengzheng Sun, "Optional and Responsive Fine-Grain Locking in Internet- Based Collaborative Systems," IEEE Transactions on Parallel and Distributed Systems,vol. 13, no. 9, pp , September, Fenkam, P.; Dustdar, S.; Kirda, E.; Reif, G.; Gall, H., "Towards an access control system for mobile peer-to-peer collaborative environments," Enabling Technologies: Infrastructure for Collaborative Enterprises, WET ICE Proceedings. Eleventh IEEE International Workshops on, vol., no.pp , 2002 Strom, R.; Banavar, G.; Miller, K.; Prakash, A.; Ward, M., "Concurrency control and view notification algorithms for collaborative replicated objects," Computers, IEEE Transactions on, vol.47, no.4pp , Apr 1998

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