the university of athens1 detecting reputation variations in p2p networks theodora dariotaki &...

The University of Athens 1

Detecting Reputation Variations Detecting Reputation Variations in P2P Networksin P2P Networks

Theodora Dariotaki & Alex Delis

Deprt. of Informatics & Telecommunications

The University of Athens

(th.dariotaki, ad)@di.uoa.gr

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•How do reputation schemes work?

•Why we might want to detect reputation variations?

A

C

B

Basic QuestionsBasic Questions

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Reputation Monitoring Mechanism Reputation Monitoring Mechanism (RMM)(RMM)

• Monitors the reputation variations of offerersMonitors the reputation variations of offerers

• Limits abrupt changes of reputation valuesLimits abrupt changes of reputation values

• New conceptsNew concepts RVM peers (Reputation Variation Monitor)RVM peers (Reputation Variation Monitor) EpochEpoch Storage Structures:Storage Structures:

• DPE:DPE: DDirectirect PPeereer EExperience Tablexperience Table

• DRE:DRE: DDirectirect RResourceesource EExperience Tablexperience Table• RT:RT: RReputation eputation TTable able (RVM Only)(RVM Only)

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Q: Where is the resource located? Q: Where is the resource located? Requester Requester qq dispatches an dispatches an AskResource message asking for message asking for

resource resource ss Offerers reply with a Offerers reply with a HoldResource message message

- - Dispatch: The message is forwarded in a scope of Dispatch: The message is forwarded in a scope of hh hops from hops from q q or or until answered by a resource holderuntil answered by a resource holder

- - Cycles: Messages received more than once, are discardedCycles: Messages received more than once, are discarded

Phase I - Resource RequestPhase I - Resource Request

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Phase II - Recommendation RequestPhase II - Recommendation Request

Q: Are the offerers trustworthy?Q: Are the offerers trustworthy? Requester Requester qq dispatches an dispatches an AskRecom message for message for allall

offerers’ reputation and resource requested. offerers’ reputation and resource requested. First-Line (FL)First-Line (FL) recommenders respond with recommenders respond with PostRecom

messages.messages.

- - Prevention of blacklistingPrevention of blacklisting

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Phase III - Evaluation of Offerer/Resource ReputationPhase III - Evaluation of Offerer/Resource Reputation

Q: Are FL-recommenders reputable? Q: Are FL-recommenders reputable? If If Direct Peer Experience > Direct Peer Experience > θθ recommendation acceptedrecommendation accepted If If qq has never communicated with a FL-recommender, has never communicated with a FL-recommender,

qq dispatches an dispatches an AskRecom message for FL’s reputation. message for FL’s reputation.Second-Line (SL)Second-Line (SL) recommenders respond with recommenders respond with PostRecom

Q: Are SL-recommenders reputable? Q: Are SL-recommenders reputable? Only ifOnly if q q has direct experience with the SL-recommender and has direct experience with the SL-recommender and Direct Direct

Peer Experience > Peer Experience > θθ the the recommendation is acceptedrecommendation is accepted

qq may rely may rely - on its own opinion - on its own opinion - on the recommenders’ opinion - on the recommenders’ opinion - on both- on both

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Phase IV – Offerer SelectionPhase IV – Offerer SelectionBaseline Reputation Scheme (BRS)Baseline Reputation Scheme (BRS)

A peer is candidate for resource downloading if both:A peer is candidate for resource downloading if both:reputation level of the reputation level of the resource holder resource holder reputation level of the reputation level of the hosted resource hosted resource

exceed a threshold exceed a threshold θθ..

Candidate peers are sorted in a listCandidate peers are sorted in a list Random selection of one-of-top reputable peers to Random selection of one-of-top reputable peers to

prevent overloading of most reputable peersprevent overloading of most reputable peers Challenge-response handshake between requester and Challenge-response handshake between requester and

resource offerer to ensure resource possessionresource offerer to ensure resource possession Download initiationDownload initiation

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Phase IV – Offerer Selection (1/4)Phase IV – Offerer Selection (1/4)RMM SchemeRMM Scheme

Step a:Step a: Early Offerer Selection Early Offerer Selection Offers with Peer/Resource reputation level < Offers with Peer/Resource reputation level < θθ are discarded are discarded

Step b:Step b: Reputation Variation Request Reputation Variation Request Requester Requester qq dispatches anonymous dispatches anonymous AskRVM messagesmessages RVMRVMss respond with respond with RVMReply messagesmessages

- reputation levels of offerers during last - reputation levels of offerers during last λλ epochs epochs

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Phase IV – Offerer Selection (2/4)Phase IV – Offerer Selection (2/4)

Relative Reputation Variation (V) Relative Reputation Variation (V) is computed for all offerersis computed for all offerersas the fraction as the fraction xx//yy

0.78

0.67

0.84

0.00.10.20.30.40.50.60.70.80.91.01.1

1 2 3 Time

Reput.Value

yx

Step c:Step c: Evaluation of Offerer Reputation Variation Evaluation of Offerer Reputation Variation

x: difference between a previous and the last x: difference between a previous and the last observed reputation level (0.67-0.84=observed reputation level (0.67-0.84=--0.17)0.17)

y: difference between the perfect reputation and y: difference between the perfect reputation and the lowest of the two reputation levels the lowest of the two reputation levels (1.00-0.67=0.33)(1.00-0.67=0.33)

52.033.0

17.0

V

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Step d:Step d: Reputation Update Reputation UpdateRequester Requester qq re-evaluates offerers’ reputation re-evaluates offerers’ reputation

Phase IV – Offerer Selection (3/4)Phase IV – Offerer Selection (3/4)

0.78

0.67

0.84

0.00.10.20.30.40.50.60.70.80.91.01.1

1 2 3 Time

Reput.Value

VxRR BRSRMM Dependence on 1 epochDependence on 1 epoch

1,2 2

i i

iiiiBRSRMM zVxzRR

General case: General case: λλ epochs epochs

x'y'

RRRMMRMM=0.79=0.79

2

)''( VxVxRR BRSRMM

Dependence on 2 epochsDependence on 2 epochs

yx

RRRMMRMM=0.75=0.75

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Step e:Step e: Final Offerer Selection Final Offerer Selection

Phase IV – Offerer Selection (4/4)Phase IV – Offerer Selection (4/4)

Candidate peers are sorted in a listCandidate peers are sorted in a list Random selection of one-of-top reputable peersRandom selection of one-of-top reputable peers Challenge-response handshake between rChallenge-response handshake between requester equester and and

resource offererresource offerer Download initiationDownload initiation

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Phase V – Resource Download & Experience UpdatesPhase V – Resource Download & Experience Updates

The The requester requester qq asks for resource asks for resource ss from the selected from the selected offerer offerer ppww by sending a by sending a DownloadReq message message

ppww sends the resourcesends the resource qq records its satisfaction in both records its satisfaction in both DPEDPE & & DREDRE tablestables

-DPE:-DPE: satisfaction concerning satisfaction concerning

selected offerer selected offerer ppww

FL-recommenders for FL-recommenders for ppww

SL-recommenders for every FL-recommender of SL-recommenders for every FL-recommender of ppww

-DRE: satisfaction concerning -DRE: satisfaction concerning downloaded resourcedownloaded resource

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ExampleExample

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33

h = 31: requester

8&10: resource holders

AskResourceHoldResource

44

7766

88 99

1111

1212

1313

1010

Requester broadcasts an AskResource (h=3)Peers forward the query

Forwarding continues until max hops h are exceeded or the resource is found

Messages received twice are discarded

55

Resource holders reply with HoldResource

found

found

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ExampleExample

11 22

33

1: requester

8&10: resource holders

AskRecomPostRecom

44

7766

88 99

1111

1212

1313

1010

Requester broadcasts AskRecom for both 8 & 10 and resource s

11 replies for 8 with PostRecom

6 & 13 reply for 10

11 & 13 are unknown to requester

6 has been proven trustworthy

55

found

found

found

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ExampleExample

11 22

33

1: requester

8&10: resource holders

AskRecomPostRecom

44

7766

88 99

1111

1212

1313

1010

Requester dispatches an AskRecom for 11 & 13

12 replies for 11 with PostRecom

9 replies for 13 (but 9 is unknown to 1)

Assume that 12 claims that 11 is trustworthy. Then 11’s recomme-ndation for 8 is accepted.

55

found

found

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ExampleExample

11 22

33

1: requester

8&10: resource holders

DownloadReq

44

7766

88 99

1111

1212

1313

1010

Requester considers 8 to be more reputable than 10 and downloads the resource from 8 (BRS)

55

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ExampleExample(RMM)(RMM)

11 22

33

1: requester

8&10: resource holders

AskRVM

RVMReply

44

7766

88 99

1111

1212

1313

1010

Requester sends anonymous AskRVM asking for reputation variations on 8&10

14141515RVM

peers1616

RVMs respond with RVMReply sending the reputation values for 8&10 during previous λ epochs

Requester computes the Relative Variation Values for 8&10 and detects abrupt changes in 8’s reputation

55

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ExampleExample

11 22

33

1: requester

8&10: resource holders

DownloadReq

44

7766

88 99

1111

121255

1313

1010

Requester downloads the resource from 10

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BRS vs. RMMBRS vs. RMM

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Time

Re

pu

t. L

eve

l

BRS RMM

λ = 3

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Discussion (1/3)Discussion (1/3)

Pseudospoofing & Shilling AttacksPseudospoofing & Shilling AttacksSmooth out abrupt changesSmooth out abrupt changesChallenge-response handshakeChallenge-response handshakeBind with real-world identitiesBind with real-world identities

Man-in-the-middleMan-in-the-middleMessage Authentication/Integrity Check Message Authentication/Integrity Check

RVM RVM anonymityanonymity impersonationimpersonation failurefailure

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Discussion (2/3)Discussion (2/3)

Number and Duration of EpochsNumber and Duration of Epochs

Average frequency Average frequency ffx x of download requests in popular peersof download requests in popular peers

Network population Network population NN

Space Overhead of RVMSpace Overhead of RVM

λλ xx NNpp ((NNpp:average # of peers assigned to a RVM):average # of peers assigned to a RVM)

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Discussion (3/3)Discussion (3/3)

Communication Cost

(k: average # of neighboring nodes, h: max # of hops)

More efficient solutions:

Select kr most reputable neighbors

Use a P2P routing protocol

(e.g. Chord with O(logN) messages, N: network population)

Anonymity cost for RVMs

(e.g. Tarzan with O(N) messages)

2h

k