the buddy system : a distributed reputation system based on social structure universität karlsruhe...
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The Buddy System : A Distributed Reputation System Based on Social Structure
Universität Karlsruhe
Stefan Fähnrich1, Philipp Obreiter1, Birgitta König-Ries2
1 Universität Karlsruhe Institute for Program Structures and Data Organization
2 Technische Universität München Faculty of Computer Science
http://www.ipd.uni-karlsruhe.de/DIANE
Workshop “Get Connected to the Mobile World - Data Management in Mobile Environments”September 21, 2004 – Ulm, Germany
Motivation: Students preparing their exercises
Amy solved: 1aNeed: 2bOffer: 1a
Bob solved: 2b
2b
1a
John: Nothing solved
Peter solved: 2a,b
Need: 2a Offer: 1a
2a
Need: 2aOffer: 1a
Need: 2a Offer: 1a
x
Distributed Reputation System
Need: 2a Offer: 1a
2a
x
Warning
What if Amy doesn‘t know Peter???
Amy
Peter John
Bob
Limitations of the existing Reputation System
1) Assement - many informations needed
- trust calculation depends on trust towards recommender
2) Self-recommendation - not possible
3) Dissemination of information - no control over dissemination
- could lead to bias
Distributed Reputation System with Social Structure
Need: 2a Offer: 1a
2a
Bob
John
Amy
Peter
WarningBails:X,Y,Z
Verifi
catio
n
Overview
• Design Space and Design Decisions for the Buddy System
• Evaluation
• Summary & Outlook
Design Space and Decision (I): Relationships
• Design Space Relationships (I)– N-ary
• bilateral• multilateral
– Direction• directed • mutual
– Type• trust, distrust, bail,…
• Design Decision (I)– bilateral– mutual– bail (buddy)
Design Space and Decision (II): Dynamics
• Design Space (II)– Establishment
• Criterion: various group rules• Procedure: majority, 100% agreement
– Cancellation• group
– agreement with notification– timeout
• bilateral– immediate, lazy, third party mediation
• Design Decision (II)– Establishment
• Criterion: same world views• Procedure: simple agreement
– Cancellation• lazy cancellation• third party mediation
John
Bob
Peter
verify
Yes,
not
ify
Bail: Johnnotif
y
OK
Why Social Structure?
1) Assessment of recommendation - Bails higher trusted
- Number bails as a clue for trust
2) Self-Recommendation - possible by stating number of bails
3) Dissemination improved - more effective (through self-recommendation)
- controllable
Evaluation
• Evaluation Goals– improvement through social structure
– can social structure itself be exploited?
• Simulation Setting: – DIANEmu
– IBR2 Benchmark
I) Evaluation
Thesis: Colluders are discovered effectively
Conclusion: Colluders have least gain - Robustness granted
II) Evaluation
Thesis: Performance increased independent from setting
Conclusion:Thesis verified - still too many vicious entities destroy usabilitiy
-0,8-0,6-0,4-0,2
00,20,40,60,8
1
standard colluders long run highentry rateco
rrel
atio
n
no DRS
standardrecommendationssocial recommendations
25% regular
Newcomers and Messages
• Thesis: Improved performance for newcomers– Defection rate decreased from 70% to 40%
• Conclusion: Thesis verified
• Thesis: Increase of messages through maintenance is lower than total messages saved.– Total number of messages decreased by 20%
– 50% less recommendation messages
– maintenance overhead low
• Conclusion: Thesis verified
Summary & Outlook
• Summary– A distributed reputation system is necessary to
uphold usability of the whole system
– conventional distributed reputation system have inherent limitations
– with a social structure those limitations can be overcome
– Buddy System introduced as a distributed reputation system with mutual, pair-based social structure.
– Evaluation of the Buddy System
• Future Work– Evidences (certificates for buddies)
– Noise
...
Any Questions ???
http://www.ipd.uni-karlsruhe.de/DIANE
Messages
Newcomers
6-way Protocol
Contract
Contract
Action
Action
Receipt
Receipt
Requester Requestee
Friends & Foes
• Each Entity has a personal list of friends and foes (and suspected foes)
• Friends and foes lists are exchanged, but only used as simple recommendations
• Directed relationships– No Self Recommendations possible
– No explicit social structure formed
Security & Transaction Protocol
• Certificates are possible with public key exchange
• gradual exchange not always possible– still „last step“ problem
• The problem of defection alone can not be solved by a transaction protocol
IBR2 Benchmark
Security & Transaction Protocol
• Certificates are possible with public key exchange
• gradual exchange not always possible– still „last step“ problem
• The problem of defection alone can not be solved by a transaction protocol
Security & Transaction Protocol
• Certificates are possible with public key exchange
• gradual exchange not always possible– still „last step“ problem
• The problem of defection alone can not be solved by a transaction protocol
Security & Transaction Protocol
• Certificates are possible with public key exchange
• gradual exchange not always possible– still „last step“ problem
• The problem of defection alone can not be solved by a transaction protocol
Security & Transaction Protocol
• Certificates are possible with public key exchange
• gradual exchange not always possible– still „last step“ problem
• The problem of defection alone can not be solved by a transaction protocol