A Trust Based Assess Control Framework for P2P File-Sharing System

Speaker ： Jia-Hui Huang

Adviser : Kai-Wei Ke

Date ： 2004 / 3 / 15

Outline

Introduction Access Control Framework Search techniques Conclusion Reference

Introduction

P2P Concept P2P file sharing allows users on the edge of

network to directly access files from on another’s drives.

Why P2P so attractive ? Provide a flexible and universal model for the

exchange of information. Success of P2P file sharing network (i.e. Gnutella,

Napster.....) But most P2P file sharing no provide access

control.

Outline

Introduction Access Control Framework Search techniques Conclusion Reference

Requirement

Access control model requirements No centralized control or support Peer classification Encourage sharing files Limit spreading of malicious and harmful digital

content

Basic idea of Framework

An access control framework based on the discretionary access control.

Each file being assigned two threshold which capture two access aspects.

Two threshold values Trust Contribution

Overall Architecture

RD ： Resource Discovery

FT ： File Transfer AC ： Access

Control

Authentication

In this framework, a peer is equipped with a 128-bit GUID number and a pair of public/private keys.

Authentication procedure Client sends authentication request. Host checks in its database. Host carries out authentication protocol.

Authentication protocol based on SSL.

Scoring system

Host peer needs to classify its client peers. Client peer is required to supply its rating

certificates for the host. Access values are evaluated via four types of

scores Direct trust Indirect trust Direct contribution Indirect contribution

Direct trust

The host’s belief on the client’s capacities, honesty and reliability based on the host’s direct experiences.

In this model, use Bethetal’s formula

denotes the trust value that peer i has in peer j

nijT 1

ijT

Direct trust ( Cont. )

n is the number of peer i’s

satisfied transactions with peer j.

is the learning rate – a real number in the interval [0,1]

must chose high enough.

Indirect trust

Host peer often encounters a client peer that it has never met.

The host’s belief on the client’s capacities, honesty and reliability based on recommendations from other peers.

Indirect trust ( Cont. )

The indirect trust calculated as

denotes the indirect trust of peer i in peer j

k is a number fixed by the host.

will be range 0 to 1 and less than or

kTTRk

ttjitij /)(

1

ijR

ijR itT tjT

Indirect trust ( Cont. )

Indirect trust calculate example

assume k = 1

Indirect trust ( Cont. )

The two main reasons why divide by k ? Avoid the client submit only one highest

recommendation. Allowing the host to specify a required number of

recommending peers.

Direct contribution

The contribution of the client to the host in term of information download/upload between them.

The direct contribution calculated as

is the direct contribution of peer j to peer I

denotes the amount information i download from j

denotes the amount information j download from i

jiijij DDQ

ijQ

ijD

jiD

Indirect contribution

The contribution of the client to the network in term of information volume exchange.

denotes the indirect contribution of peer j from peer i’s point of view.

k

ttjitij QTP

1

ijP

Granting access ( Cont. )

The client’s overall trust and contribution values calculated as

value depending on host’s control policy.

ijRijTij RCTCA

ijPijQij PCQCB

1 RT CC

1 PQ CC

PQRT CCCC 、、、

Granting access

Before making a file available for sharing, a host peer defines two thresholds value for the file.

Any client peer who has equal to or greater than the corresponding thresholds can access the file

Trust and contribution management After completing a download operation, client

peer has to issue the host peer a rating certificate.

Rating certificate contains the direct trust and direct contribution value based on the transaction’s satisfaction level.

Rating certificate

Rating certificate format

Satisfaction level

Evaluate satisfaction level based on the download speeds and file quality.

Five levels of satisfaction Good Fair T unchanged Poor Corrupted Unknown Harmful or malicious add to the black list

0T

)1(1 nT )2/(1 nT

)1(1 nT

Local file system

In local storage it stores follow Received certificates in which the peer itself is the

recommended peer. Certificates which the peer issued to other peers. A black list of peers who it believes to have

committed malicious acts.

Framework interaction procedure

Outline

Introduction Access Control Framework Search techniques Conclusion Reference

Metrics

Some metrics for evaluate the effectiveness of search technique. Cost

Bandwidth

consumed over every edge in the network on behalf of each query.

Processing cost

processing power consumed at every node on behalf of each query.

Metrics

Quality of results Satisfaction of query

user specify a value Z, if the number of result is equal or more than Z, the query is satisfied.

Time to satisfaction

the time of result arrive.

Search techniques

Inefficiency search blind search (BFS)

Three efficient search techniques： Iterative deepening Directed BFS Local indices

Blind search

Node forward to all their neighbors

Find max number of results

But inefficiency

Iterative deepening

Satisfaction is the metric of chose. Multiple breadth-fist searches are initiated

with successively larger depth limits until query is satisfied or max depth reached.

Time cost smaller than blind search

Iterative deepening

ex.

if policy is Source node initiates a

BFS of depth a. When depth reach, if

query not satisfied then continue to depth b and c

},,{ cbaP

Directed BFS

Minimizing response time. DBFS technique send query messages to

just a subset of its neighbors. In order to intelligently select neighbors, node

will maintain statistic on its neighbors.

Directed BFS

Some heuristic can help us to select the best neighbors Highest number of results for previous query. Response messages taken the lowest average

hop. Has forwarded the largest number of messages. Shortest message queue.

Local indices

Maintaining a high satisfaction rate and number of results while keeping low costs.

Node maintains an index over the data of each node within r hops of itself.

Parameter r is adjustable and independent of total size of network.

It must notify when host joint network Node index the leaving node’s collective will

remove after a timeout.

Local indices

ex.

if policy is Query source will send the

query message out to all its neighbors at depth 1.

All node at depth will process and forward to depth 2.

Depth not in list, it forward directly.

Process continue to depth 5

}5,1{P

Outline

Introduction Access Control Framework Search techniques Conclusion Reference

Conclusion

The framework satisfies the requirements of access control for P2P file-sharing system by trust and contribution model, and the implemented contribution work effectively as a payment scheme that giving incentive for users to share their resource.

The disadvantage is some overheads in validity of signatures in the rating certificate.

Reference

B. Yang and H. Carcia-Molina. Efficient Search in peer-to-peer Networks, ICDCS 2002, Jul 2002

Thomas Beth and Malte Borcherding and Birgit klein Valuation of trust in open network