To share services, mobile devices may need to locate reputable in-range providers and, to do so, they may exchange ratings with each other. However, providers may well tweak ratings to their own advantage. That is why we have designed a new decentralized mechanism (dubbed MobiRate) with which mobile devices store ratings in (local) tamper-evident tables and check the integrity of those tables through a gossiping protocol. We evaluate the extent to which MobiRate reduces the impact of tampered ratings and consequently locates reputable service providers. We do so using real mobility and social network data. We also assess computational and communication costs of MobiRate on mobile phones.

1. U C L (daniele quercia)

2. I’m finishing my PhD @

3. U niversity C ollege L ondon

4. <My Research>

5. Ratings on ...

6. Ratings on phones

7. MobiRate: how mobiles collect & store ratings

8. Why ratings on mobiles?

9. Daniele Quercia Situation : People exchange digital content

10. drowning user (content overload) help! who will come to the rescue?

11. Proposal: Accept content only from reputable people

12. how mobiles collect & store ratings

13. collect > store > use

14. Ignorant Forgers Liars collect > store > use

15. Ignorant Forgers Liars [Suspected]

16. Ignorant Forgers Liars [Suspected] [Exposed]

17. Ignorant Forgers Liars [Suspected] [Exposed] [Filtered Out]

18. Ignorant Forgers Liars [Suspected] [Exposed] [Filtered Out] Work done: AAAI,KDD, ICDM,...

19. Ignorant Forgers Liars [Suspected] [Exposed] [Filtered Out] Work done: AAAI,KDD, ICDM,... ~ø ~ø

20. Ignorant Forgers Liars [Exposed] [Filtered Out] Work done: AAAI,KDD, ICDM,... MobiRate collect > store

21. How to collect & store ratings?

22. 1.Log (credentials) 2. Gossip (to check each credential)

23. 1.Log (credentials) 2. Gossip (to check each credential)   Impractical 

24. Idea behind MobiRate

25. Let’s make it practical...

26. 1.Sealed Log (of credentials) 2. Gossip (to check seals only)

27. 1.Sealed Log (of credentials) 2. Gossip (to check seals only)    Practical

28. 1.Sealed Log (of credentials) entry (rating) “ seal” (for the entry)

29. 1.Sealed Log (of credentials) entry (rating) “ seal” (for the entry) “ hash chain” binding whole table

30. Assumption ID is a unique public key

31. Gossiping: To whom?

32. To witnesses [slow down]

33. Audit! [slow down] What witnesses do

34. Audit! [slow down] What witnesses do Why?

35. If one is ignorant If one is a forger [Suspected] [Exposed]

36. Who are my witnesses Those who will share content with me

37. . Who are my witnesses Like-minded familiar strangers

38. 1.Sealed Log (of credentials) 2. Gossip (to check seals only)    Practical

39. Does MobiRate work?

40. Mobility Traces AND Social Networks Reality Mining

41. Does MobiRate work?

42. Does MobiRate work? <1> Is it robust to malicious individuals? <2> Does it run on phones?

43. <1> robust The f factor

46. MobiRate Oracle

47. MobiRate reduces f!!!

48. <2> run

49. “ heaviest” protocol runs < 2sec

50. “ longest” protocol completed in 2.5ms (if Bluetooth 100kb/s)

51. MobiRate works  robust  runs on phones

52. Ignorant Forgers is a step towards...

53. … rescuing drowning user help!

54. Daniele Quercia All this on … mobblog mobirate

56. Assumption ID is unique public key

57. If not unique  Sybil attacks!

58. Ignorant Forgers Liars [Exposed] MobiRate (eg, Sybils) collect > store > use

59. Ignorant Forgers Liars [Exposed] Filtered Out by [ICDM07] MobiRate (eg, Sybils) collect > store > use [ICDM07] Lightweight Distributed Trust Propagation