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