1. Peer-to-Peer Reputations
Prashant Dewan
Advisor: Dr. Partha Dasgupta
1 January 2019
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Peer-to-Peer Reputations

2. Peer-to-Peer Reputations
Goals
To facilitate ‘secure’ transactions among peers in a completely decentralized system
Secure implies
Peers can be authenticated
The chance that a peer gets cheated in a transaction is low
A peer is either forced or motivated against cheating
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Peer-to-Peer Reputations

3. Peer-to-Peer Reputations
Possible Techniques
Micropayments
Expensive
Waste resources
A peer with large volume of resources can break it
Other Distributed Security Systems
SDSI, Dynamic Trust Management, Groove,Publius
All of them use a central component
All of them are dependent on some form of ‘Authority’
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Peer-to-Peer Reputations

4. Peer-to-Peer Reputations
What is a reputation?
The general estimation in which a person is held by the public – Oxford Dictionary
A Recommendation is the ‘certificate of satisfaction’ given by one entity (requestor) to the other (provider) after a transaction ( eg. A File Download)
The Reputation of a person ( or an entity) is the sum of the ‘recommendations’ received by the person (or an entity) from others (people or entities) with whom it has transacted in the past.
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Peer-to-Peer Reputations

5. Calculation of Reputation
Recommendations
B  A = 5
C  A = 3
D  A = 4
Alice’s Reputation
5+3+4 = 12
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Peer-to-Peer Reputations

6. Peer-to-Peer Reputations
Challenges
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Peer-to-Peer Reputations

7. Peer-to-Peer Reputations
Benefits
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Peer-to-Peer Reputations

8. Peer-to-Peer Reputations
Self-Certification
Certificate Authority
User does not have to trust a third party certificate provider which might be a vulnerability
User can separate transactions by having multiple identities
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Peer-to-Peer Reputations

9. Peer-to-Peer Reputations
Liar Farms 5 10
Certificate Authority 2 5 4 8 4 2 4
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Peer-to-Peer Reputations

10. Peer-to-Peer Reputations
IP Based Safeguard d
Rep 1 29 2
12.5 3
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Peer-to-Peer Reputations

11. Peer-to-Peer Reputations
IP Based Safeguard
Most peers are interested in relative ranks of other peers
Adjustment of ranks has a ‘small’ effect on the relative ranks
Network Size=1000 peers
Mean Rank Difference= ±0.81 (95% confidence)
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Peer-to-Peer Reputations

12. Elicitation-Storage Protocol
The “requestor” selects the highest-reputation provider from a list of possible providers
The requestor verifies the recommendations of the provider
Checks if the signature on the recommendations match the identity certificate sent along with the recommendation
Once verified, the “provider” provides the content
The requestors issues the recommendation to the provider
The provider stores the recommendation and the identity of the requestor
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Peer-to-Peer Reputations

13. Peer-to-Peer Reputations
Application Areas
eBay, Amazon, Monster…
School Friends, Family…
CORE, CONFIDANT & SPRITE…
SMTP, Web Services…
Gnutella, Kazaa & Morpheus…
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Peer-to-Peer Reputations

14. Peer-to-Peer Reputations
P2P & NAT
Port
Session Initiation Protocol
Needs Servers
TCP Splicing
Very complicated
UDP Solutions
Waste of Bandwidth
UPnP – A standard being developed by Microsoft and allies.
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Peer-to-Peer Reputations

15. Peer-to-Peer Reputations
Name Service
Server:
Domain1: superpeer1
Domain2: superpeer2
Bob
ASU: David is Superpeer
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Peer-to-Peer Reputations

16. Peer-to-Peer Reputations
Name Service ..
Alice Logs in in New York
Connects to the Domain of NYU
Informs ASU super peer of current location
Bob contacts ASU superpeer and gets the address of Alice
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Peer-to-Peer Reputations

17. Peer-to-Peer Reputations
Name Service ..
David Logs out
Asks all domain members for the next superpeer
Carol becomes the superpeer
David Transfers current locations to Carol and Logs out
Carol Informs the public server
Bob tries to reach David and Fails and gets to Carol via public server
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Peer-to-Peer Reputations