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


•How do reputation schemes work?

•Why we might want to detect reputation variations?

A

C

B

Basic QuestionsBasic Questions


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)


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


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


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


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


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


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


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


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


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


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


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


ExampleExample

11 22

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


ExampleExample

11 22

33

1: requester


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


ExampleExample

11 22

33

1: requester


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


ExampleExample

11 22

33

1: requester


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


ExampleExample(RMM)(RMM)

11 22

33

1: requester


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


ExampleExample

11 22

33

1: requester


DownloadReq

44

7766

88 99

1111

121255

1313

1010

Requester downloads the resource from 10


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


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



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)



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

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

Documents

offerers reputation

fls reputation

reputation schemes

resource s requester

postrecom q

resource offerer

university of athens4

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