Controlling Collaborative Systems

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Controlling Collaborative Systems

• -Srinivas Krishnan
• Dept of Computer Science
• UNC-Chapel Hill

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Collaborative Systems
Shared Resource
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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

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Requirements for Access Control Systems

• Access Control Systems are built in layers

A U D I T
Permissions
Notifications
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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)

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ACL and CCL
ACL
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.

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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

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Role Based Access Control (Sandhu et al)

• Permissions are assigned to roles
• User authenticates in a 2 step process

Request
Permissions
Roles
Users
Role
Resources
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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

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Spatial Access Control

• Divides collaborative environment into spaces

Collaborative Environment
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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
User1
User1
Space B
Space C
User2
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Test Setting
Taking the Test
Correction
Results
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Implementation Issues

• Order of updates and notification matter
• Cannot depend on a global clock to be
  synchronized

Remove Access to Bob (Op2)
Give Access to Bob (Op1)
Permissions
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Solution for Order of Updates

• Most fine-grained locking operations require
  Total-Ordering

Check Update Counter
gt Local
Remote Counter
lt Local
Adopt Remote Counter
X

Perform Operation
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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

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Optimistic Control

• Make the user ask forgiveness not permission
• A similar system exists in UNIX with sudo.
• However, changes are permanent

Fire in Building
John
John
Move Resource
Everyday access
Resource
Access Denied
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Optimistic Access Control

• Needs different points of entry

A U D I T
ElevatedEntry
Normal Entry
Access Control
Resource
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Optimistic Control
New State
Guaranteed Protection
Compensating
Transaction
No Protection
New State
Transaction
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Auditing Optimism
Resource
Transaction
Compensation
Verify
Verification Classes
Users
Integrity Rules must be verified at all times
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Simple Optimistic Access Control
Auth Modules
Verify
Write to File
Transaction Checker
Logger
File
PTP LOG
Log
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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

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Architecture
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Improving Motion
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Summary

• Access Control essential for maintaining a secure
  Collaborative Environment
• Access Control can introduce lag and degrade a
  users experience
• Optimistic Access Control algorithms can be used
  to allow users to experience native performance

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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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• Questions ?