1 / 23

DIANE Project

Universität Karlsruhe GERMANY. A Case for Evidence-Aware Distributed Reputation Systems Overcoming the Limitations of Plausibility Considerations. The Second International Conference on Trust Management 29 March - 1 April 2004 – Oxford, UK. Philipp Obreiter. Universität Karlsruhe

parnellj
Télécharger la présentation

DIANE Project

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Universität Karlsruhe GERMANY A Case for Evidence-Aware Distributed Reputation Systems Overcoming the Limitations of Plausibility Considerations The Second International Conference on Trust Management 29 March - 1 April 2004 – Oxford, UK Philipp Obreiter Universität Karlsruhe Institute for Program Structures und Data Organization DIANE Project http://www.ipd.uni-karlsruhe.de/DIANE

  2. 1. service request 2. service provision 3. receipt 4. disrecommendation (”Anne did not provide the service”) 5. assessment of the disrecommendation (”Did Anne defect or did Bob defame?”) Motivation (1): Current State Anne Bob Chris Problem: Assessment of recommendations is equivalent to the Byzantine Generals Problem Approach: Base such assessment on plausibility considerations • How trustworthy is the recommender? • Does his statement correspond to one’s own prior beliefs?

  3. 1. service request 2. service provision 3. NR-receipt 8. disrecommen-dation (”Bob issued defamation”) 4. NR-disrecommendation 5. receipt? 6. receipt! 7. refutation the disrecommendation Motivation (2): Target State Anne Bob Chris Approach: Make use of non-repudiable tokens (=evidences) Solves the Byzantine Generals Problem: • the defamation is refuted by presenting the receipt • Bob’s misbehavior is proven by presenting the receipt/defamation

  4. Overview • Limitations of plausibility considerations • Concept of Evidences • Overcoming the limitations: 3 patterns • Relationship to existing approaches

  5. Distributed Reputation Systems: System Model Entity A Entity B Transactions local instance of the DRS local instance of the DRS Recommendations information system

  6. Limitations of Plausibility Considerations (1) Limitations (Part 1) • disadvantages for newcomers • Chris cannot make use of plausibility • recommendations unrelated to behavior • Anne is disrecommended in spite of the service provision • Anne cannot self-recommend • ineffective dissemination of recommendations • recommendations authenticated but repudiable 1. request Anne Bob 2. provision 3. receipt Chris 4. disrecom-mendation 5. assessment

  7. Limitations of Plausibility Considerations (2) Limitations (Part 2) • unobservable recommendation behavior • Anne does not know about the defamation • unrecognized defamations • e.g., if Chris is a newcomer • unrecognized praising • same as for defamations • dissemination of assessment results • Chris’ assessment result cannot be reproduced by others 1. request Anne Bob 2. provision 3. receipt Chris 4. disrecom-mendation 5. assessment

  8. coupling coupling verification documented by evidences available evidences Concept of Evidences: Comparison with Plausibility no coupling plausibility considerations undocumented Assessment Actual Behavior Evidences Coupling of Actual Behavior and Assessment • only for documented behavior (inherent restrictions!)  plausibility considerations still necessary for undocumented behavior

  9. Concept of Evidences: Inherent Restrictions Inherent Restrictions • ensue from the criterion of incentive compatibility • partly compromise the availability and truthfulness of evidences 1. Asymmetry of Issuance there exists a receipt that is not acknowledged  some behavior not documented (Coordinated Attack Problem) 2. Issuance of Negative Evidences an entity does not disseminate negative evidences about itself  lack of negative evidences 3. Untruthfulness Evidences colluding entities could mutually attest good behavior  evidence-awareness cannot solve the problem of praising

  10. Overcoming the Limitations: Three Patterns (1) 1./2. request/provision self-recom-mendation Anne Bob 3. NR-receipt 5. receipt? 4. NR-disrecom-mendation Chris 6. receipt! 6. receipt! verifiable assessment result 8. disrecommendation 8. disrecommendation 7. refutation 7. refutation plausibility-less assessment • Transferability of Evidences • recommendation unrelated to behavior () • disadvantages for newcomers () • dissemination of assessment results  • ineffective dissemination of recommendations 

  11. Overcoming the Limitations: Three Patterns (2) 1./2. request/provision Anne Bob 3. NR-receipt 5. receipt? 4. NR-disrecom-mendation Chris 6. receipt! 8. disrecommendation 7. refutation If Bob does issue the receipt, • Bob’s defamation is refutable • Bob won’t defame If Bob does not issue the receipt, • Bob defects • Anne won’t transact with Bob Screening of Recommendation Behavior • unobservable recommendation behavior

  12. Overcoming the Limitations: Three Patterns (3) 1./2. request/provision Anne Bob 3. NR-receipt 5. receipt? 5. receipt? 4. NR-disrecom-mendation 4. NR-disrecom-mendation Chris 6. receipt! 8. disrecommendation 7. refutation Anne is given the chance to provide refuting evidences has to be non-repudiable, otherwise it is ignored Policy-based Restriction of Defamations • unrecognized defamations () • ineffective dissemination of recommendations  • unobservable recommendation behavior

  13. Overcoming the Limitations: Summary

  14. self-organized punishment for misbehavior Plausibility based distributed reputation system Evidence based assessment by a central authority coupling of assessment with actual behavior Relationship to Existing Approaches Evidence aware distributed reputation system Plausibility considerations by a central authority

  15. Summary and Future Work Summary • in distributed reputation systems, the truthfulness of recommendations has to be assessed, • existing approaches rely on plausibility considerations, • there are several limitations of plausibility, • we propose the use of non-repudiable tokens (evidences), • evidences partly couple assessment and actual behavior, • evidences allow for transferability, screening and policies, • evidence awareness overcomes virtually every limitation Future Work • examine the design space of the policies and the verification process • implement and evaluate an evidence-aware distributed reputation system

  16. H N T A K S ...for your attention http://www.ipd.uni-karlsruhe.de/DIANE

  17. Appendix

  18. Chris Bob Anne local instance of the DRS local instance of the DRS local instance of the DRS Transaction Recom-mendation Distributed Reputation Systems: System Model Entity A Entity B Transactions local instance of the DRS local instance of the DRS Recommendations Example: Recommendee Recommender Assessor (=Recipient)

  19. Concept of Evidences: Basics Evidence • non-repudiable token • issued by an entity (evidencer) • regarding the behavior of another entity (evidencee) Types of Evidences • receipt: evidencer attests that its peer has executed an action • non-repudiable recommendation: evidencer (=recommender) may be linkedto its recommendation • contract: evidencer attests to have agreed on some terms • non-repudiable action: evidencer may be linked to its own action

  20. issuance of recommendations dissemination of recommendations facts cannot be credibly communicated recommender in charge of the dissemination behavior of others good conduct of oneself cannot self-recommend impact of recommendation depends on own reputation Limitations (1): Recommender limitations for the recommender

  21. incertitude about recommendations incertitude about effectiveness the amount and contents of recommendations is unknown doubts about the effectiveness of the reputation system impact on the reputation system effective pruning effective dissemination impact on transactions necessity of pro-active defense unknown transaction peer might not know about relevant recommendations cannot adapt transactional behavior to the peer’s recommendations doubts about the coupling of behavior and reputation lack of incentives lack of protection no protection against defamations good behavior might not result in good reputation Limitations (2): Recommendee limitations for the recommendee

  22. difficulties of assessing recommendations difficulties of disseminating assessment results plausibility considerations may lead to inappropriate assessment disseminated result is subject to plausibility considerations plausibility considerations infeasible plausibility considerations false assessment necessitates a minimum of background information plausibility considerationsmay lead to wrong assessment overestimation due to praising underestimation due to defamation betrayal by transaction peers synergies with well-behaving transaction peers are not exploited Limitations (3): Assessor limitations for the assessor

  23. Overcoming the Limitations: Summary

More Related