ACCESS CONTROL AND JOINT MANAGEMENT FOR

COLLABORATIVE PEER GROUPS

Wenhua Qi

School of Electronic and Information Engineering , Beihang University, Xueyuan Rd., Haidian District, Beijing, China

Keywords: Peer groups, Access control, Joint management, JXTA technology.

Abstract: Collaborative peer groups means that multiple self-organizing peers aggregating in a controlled manner to

accomplish some collective goals. Peer groups share the properties of peer-to-peer overlay network, includ-

ing full decentralization, symmetric abilities, and dynamism, which make security problems more compli-

cated. Most prior work focused on authentication, group key management and communication security.

However, access control is an important precondition of many security services. Intend for a pure decentral-

ized model without centralized server, our framework employs a distributed delegation authorization

mechanism and proposes an authority selection scheme. Multiple authorities could exist in this design,

which could avoid single point of failure. Based on the role-based trust management language RT, this pa-

per presents an attribute-based access control framework, and describes a formal joint authorization protocol

under voting scheme, to satisfy security requirements of multiple peers. We also introduce our implementa-

tion experience by applying JXTA technology.

1 INTRODUCTION

In some cases, multiple self-organizing peers aggre-

gate in a controlled manner, and use multiway com-

munication primitives to accomplish their collective

goals. Collaborative peer groups (Sunderam, 2003.

Gong, 2002) is introduced to refer to such peer-to-

peer networks, which are a strong and flexible struc-

ture to enable coordination between applications,

server-client, and peers in networks. Group settings

may be synchronous or asynchronous manner, and

communication models vary from one-to-many or

few-to-many to any-to-any.

Collaborative Peer groups share the properties of

peer-to-peer overlay network, including full decen-

tralization, symmetric abilities, and dynamism,

which make security problems more complicated.

Most prior work has been done in the context of

group membership authentication, group key man-

agement (Rodeh, 2000), and communication secu-

rity. However, access control is an important pre-

condition of many security services. Conventional

group access control mechanisms make authoriza-

tion decisions based on the identity of requester,

such as Gothic (Judge, 2002), Intergroup (Agarwal,

2001). Unfortunately, in distributed environments,

members often are unknown to one another; access

control based on identity may be ineffective.

Upon the analyses, distributed authorization and

access control mechanisms need to be implemented

in collaborative peer groups. To avoid single point

of failure and enhance scalability of the system, in-

stead of using a centralized model (Judge, 2002), we

employ a distributed delegation authorization

mechanism and propose an authority selection

scheme. Multiple authorities could exist in this de-

sign, reducing both the overhead and the response

time of group authority. Based on the role-based

trust management languages RT (Li, 2002), our

work presents an attribute-based access control

framework and describes a formal joint authoriza-

tion protocol under voting scheme, to satisfy secu-

rity requirements of multiple peers. By applying

JXTA technology, we also introduce our implemen-

tation architecture and experience.

2 AUTHORITY SELECTION IN

PEER GROUPS

Intend for a fully distributed peer group without cen-

tralized control over group membership, our frame-

work presents that a peer within the group could

Qi W. (2006).

ACCESS CONTROL AND JOINT MANAGEMENT FOR COLLABORATIVE PEER GROUPS.

In Proceedings of the International Conference on Security and Cryptography, pages 83-86

DOI: 10.5220/0002099200830086

 SciTePress

propagate its own attributes to other peers. We pro-

posed a quality model based on a set of quality crite-

ria. For each criterion, we provide a definition, indi-

cate its granularity, and provide rules to compute its

value for a given peer. Thus, an authority will dele-

gate its authority property to a neighbor which has

high quality criteria. This allows the new peers to

accept new member into the peer group, reducing

both the overhead and the response time of author-

ity.

2.1 Peer Group Quality Model

To differentiate the peers of a group during authority

selection, their non-functional properties need to be

considered. We consider five generic quality criteria

for each peer: (1) cost (2) capacity, (3) age, (4)

global trust value, and (5) neighbor link value.

Cost: Given a service to a peer i, such as relay ser-

vice, we define cost as the resource cost of a service

provider has to pay for providing the service.

Capacity: We define capacity as the ability of a peer

to process and relay queries and query responses.

Age: We define age as the length of time up to now

since a peer joins the network up to present.

Trust: We may adopt the trust model EigenRep

(Kamvar, 2003) and define trust as the global trust

value of a peer.

Link: Peers also regularly link to other peers. We

define link as the number of links from i that can

reach after at most one indirection.

Given the above quality criteria, the quality vector

of a peer i is defined as follows.

Q(i)=(Price

, Capacity

, Age

, Trust

, Link

)

2.2 Authority Selection by

Optimization

In our approach, when the group members increase,

the authority peer collects information about the

QoS of its neighbors, and a quality vector is com-

puted for each of the peers. Based on the quality

vectors, a peer with high quality criteria will be se-

lected as the authority peer. This selection process is

based on the weight assigned by the authority to

each criterion, and a set of policy-defined constraints

expressed using a simple express language. Exam-

ples of constraints that can be expressed include ca-

pacity constraints and trust constraints. By merging

the quality vectors of all these n neighbors, a matrix

Q=(Q

i,j

;

1;15in j≤≤ ≤ ≤

) is built, in which each

row Q

corresponds to a peer while each column cor-

responds to a quality dimension. A Simple Additive

Weighting (SAW) (L, 1981) technique is employed

to select authority peers in this design, including two

phases:

1. Scaling Phase. Some of the criteria could be nega-

tive, i.e., the higher the value, the lower the quality,

such as Cost. Other criteria are positive, i.e., the

higher the value, the higher the quality, such as Ca-

pacity. For negative criteria, values are scaled ac-

cording to

max

max min

−

. For positive criteria,

values are scaled according to

min

max min

ij j

−

2. Weighting Phase. The following formula is used

to compute the overall quality score for each

neighbor:

() ( )

iijj

Score peer V W

=∗

∑

(0 ≤ Score (peer

)

≤

where W

∈

[0, 1] and

∑

. W

represents

the weight of criterion j. The authority expresses

their preferences regarding QoS by providing values

for the weights W

3 JOINT MANAGEMENT

This section presents a role-based trust model and

joint authorization protocol to satisfy the access con-

trol requirement of peer groups.

3.1 Access Control Policy

In a fully distributed group, our framework adopts

credential in trust management (Li, 2002) as authen-

tication method. Role is defined as A.r(h

, " ,h

where A is entity name，r is role name. A Role may

include zero or more restriction parameters h

. Ac-

cess Policy has the form of

rr<←, vote>, where

←

is access rule. When a peer requests the role

of r

, the policy statement is checked. vote has one

of the following forms:

1) true: vote is always true；

2) fixed(r, m, f): A voting is called among members

of the r role. If k votes are received and f

k are yes,

then vote is true(m, k

∈

integer; k ≥ m; f∈ [0,1]).

3) dynamic(r, f

, f

): This is equivalent to fixed(r,

SECRYPT 2006 - INTERNATIONAL CONFERENCE ON SECURITY AND CRYPTOGRAPHY

m=n

, f

), where the role r has n members(m,

∈ integer; f

, f

∈ [0,1]).

3.2 Joint Authorization

The joint authorization protocol based on JXTA

technology has five phases, which are group initiali-

zation, searching group advertisement, authoriza-

tion request, voting, and PGC issuance.

1) Group Initialization. The group authority peer

initializes the local secure environment by creating a

secure peer group, and then publishes the secure

peer group advertisement into the network. The

group adv. contains access control policy of peer

groups and various parameters such as group name,

voting type, etc.

2) Searching Group Advertisement. When a new

peer wants to join the group, it must firstly obtain

the advertisement of its attributive peer group. In

this design peers have two ways to get this informa-

tion. Peers may discovery the authorization service

advertisement from the rendezvous peer or by flood-

ing.

3) Authorization Request. Having the advertise-

ment message, new coming peer may connect with

the corresponding authority peer. The new peer will

generate a group certificate issuance request contain-

ing its desired privileges.

4) Voting. Upon receipt of authorization request, the

authority peer first verifies the signature. In a fully

distributed peer group, the request is either accepted

or rejected by the collective set of current members.

The authority peer then propagates the request to

call a vote of peers. According to the policy, multi-

ple peers authenticate the attribute of a requester,

vote, and reply with a signed message to approve or

reject the authorization request.

5) PGC Issuance. Once enough votes are collected,

the authority verifies all the votes, and decide

whether to accept the new node as a member. If the

requester is qualified, the authority will issue the

group certificate to it and update the related peer

group information. Then, the new node can join the

secure peer group.

4 IMPLEMENTATION

We implemented the distributed access control in

peer-to-peer collaborative systems using Java pro-

gramming language. The communication facility

among peers is provide by JXTA(Sun, 2002.

Altman, 2003), an overlay network middleware

messaging system. The measurements are performed

on 32 nodes with a high-speed LAN, and each node

is the Intel Nocona Xeon 2.8GHz, 2G RAM Linux

machine. As the setup phase of the peer group, the

Group Authority creates and publishes the group au-

thorization service advertisement. All group access

control protocol messages are encapsulated within

standard JXTA messages. To satisfy the distributed

authorization requirement and balance the group au-

thority overhead, the group authority will republish

the authorization service advertisement after delegat-

ing the authority attribute to another group member.

The group authorities may receive multi-requests

in a short time interval. Figure 1 shows the average

join coat for the centralization and delegation. The

number of current group members is 30, and the

threshold is 30%. In Figure 2，we plot the accumu-

lated joining ratio against time, and contrast differ-

ent authorization approaches with 40 new nodes. We

can see that after 20 seconds, the success joining ra-

tios vary from 12.5% for a centralized scheme, 50%

for two authorities, to 75% for three authorities.

0 4 8 12 16 20 24 28

Join Group Requesters (n) threshold=30%

Average Join Time (seconds)

centralization authority

delegation authority

5 10 15 20 25 30 35 40 45 50

100

Time

(

seconds

)

Accumulated joining ratio(%)

Group GA =3

Group GA =2

centraliztion

Figure 1: Average Join Cost of Dynamic Requesters. Figure 2: Average Join Cost of Dynamic Requesters.

ACCESS CONTROL AND JOINT MANAGEMENT FOR COLLABORATIVE PEER GROUPS

5 RELATED WORK

Many researches have been accumulated on security

in multicast groups. Gothic (Judge, 2002) provides

security service for IP-Multicast. An external access

control server performs authentication and authori-

zation based on PKI certificates. The Antigone

(McDaniel, 1999) utilizes a centralized access con-

trol approach in which member access is mediated

by a Session Leader.

Sconce(Kim, 2003) presents an admission control

framework in peer groups, which treats peer groups

as a flat structure where all peer nodes have identical

rights and responsibilities. Thus Sconce, which lacks

the attribute of peers, can not simplify authorization

in collaborative environments. JXTA presents a se-

curity mechanism also based on PKI certificates

(Altman, 2003). Intergroup (Agarwal, 2001) pro-

vides access control by using an authorization ser-

vice, Akenti (Thompson, 2003), which provides a

coarse granularity for access control.

Most of the systems described above provide ac-

cess control based on identify of participants, in-

stead, this paper adopts attribute-based access con-

trol in group. Based on the RT languages (Li, 2002),

our work presents a fine-grained access control

framework for collaborative peer groups. Mean-

while, based on the policy model, this paper empha-

sizes the need of joint management for peer groups.

Joint authorization efficiently provides security for

communication and data resources shared by multi-

ple peers.

6 CONCLUSION

This paper presents a fine-grained and attribute-

based access control framework for collaborative

peer groups. We propose a distributed delegation

authorization mechanism to avoid single point of

failure. In order to simplify authorization and access

control in collaborations, access control decisions

are made based on authenticated attributes of the

peers, which improve flexibility of decentralized au-

thorization. By applying JXTA technology, this pa-

per describes a formal joint authorization protocol

under voting schemes, to satisfy security require-

ments of multiple peers.

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