Controlling Collaborative Systems

-Srinivas Krishnan

Dept of Computer Science

UNC-Chapel Hill

Collaborative Systems

Shared Resource

Access Control

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

AUDIT

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.

ACLCCL

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

SpaceA

SpaceB

SpaceC

User1 User1

User2

Test Setting Taking the Test

Correction Results

ProfessorStudent Student

Student

StudentProfessor

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 < LocalAdopt 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

AUDIT

Normal Entry

ElevatedEntry

Optimistic Control

Guaranteed Protection

No Protection

Transaction

Transaction New State

New State Compensating

Auditing Optimism

Verification Classes

Integrity Rules must be verified at all times

ResourceTransaction Compensation

Verify

Users

Logger

Simple Optimistic Access Control

File

AuthModules

TransactionChecker

Write to File

PTP LOG

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

Requester L1/L2 Peer

Distributed Search

L1/L2 Peer

Perform Op

Peer

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. 2005. Access control in collaborative

systems. ACM Comput. Surv. 37, 1 (Mar. 2005), 29-41. Povey, D. 2000. Optimistic security: a new access control paradigm. In

Proceedings of the 1999 Workshop on New Security Paradigms (Caledon Hills, Ontario, Canada, September 22 - 24, 1999). NSPW '99. ACM Press, New York, NY, 40-45.

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. 994-1008, September, 2002.

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, 2002. WET ICE 2002. Proceedings. Eleventh IEEE International Workshops on , vol., no.pp. 95- 100, 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.458-471, Apr 1998

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