Secure Group Communication in Grid Environment

Dr Sudha Sadasivam G, Ruckmani V & Anitha Kumari K
International Journal Of Security (IJS), Volume (4): Issue (1) 17
Secure Group Communication in Grid Environment
Dr Sudha Sadasivam G sudhasadhasivam@yahoo.com
Professor/Department of Computer Science
PSG College of Technology
Coimbatore – 641 004, India.
Ruckmani V ruckmaniv@yahoo.com
PhD Research Scholar/Department of Computer Science
Anitha Kumari K kesh_chse@yahoo.co.in
ME (SE) Student/Department of Computer Science
ABSTRACT
A Grid is a collection of resources that are available for an application to
perform tasks. Grid resources are heterogeneous, geographically distributed
and belong to different administrative domains. Hence security is a major
concern in a grid system. Authentication, message integrity and
confidentiality are the major concerns in grid security. Our proposed approach
uses a authentication protocol in order to improve the authentication service
in grid environment. Secure group communication is brought about by
effective key distribution to authenticated users of the channels serviced by
resources. The proposed approach facilitates reduced computation and
efficient group communication. It also ensures efficient rekeying for each
communication session. The security protocol has been implemented and
tested using Globus middleware.
Keywords: authentication, grid computing, grid security, multicasting, encryption.
1. INTRODUCTION
Grid protocols and technologies are being adopted in academic, government,
and industrial organizations. Grid computing facilitates remote access to high–
end resources for computation and data intensive jobs. Researchers can
access heterogeneous and geographically distributed hardware and software
resources efficiently. Two important requirements in grid include the formation
of virtual organizations (VO) dynamically and establishment of secure
communication between the grid entities. A VO is a dynamic group of

individuals, groups, or organizations that have common rules for resource
sharing [1].
Security in computational grids encompasses authentication, authorization,
non-repudiation, integrity, confidentiality and auditing. To avoid the illegal
users from visiting the grid resources strong mutual authentication between
grid entities should be guaranteed. Password-based authentication is
extensively used because of its simplicity. Authorization allows a specific
permission for a particular user on a specified resource (channels).
Confidentiality of information in a VO should also be ensured [4]. The
necessity for secure communication between grid entities has motivated the
development of the Grid Security Infrastructure (GSI). GSI provides integrity,
protection, confidentiality and authentication for sensitive information
transferred over the network in addition to the facilities to securely traverse
the distinct organizations that are part of collaboration [2]. Authentication is
done by exchanging proxy credentials and authorization by mapping to a grid
map file. Grid technologies have adopted the use of X.509 identity certificates
to support user authentication. GSI is built on top of the Transport Layer
Security (TLS) protocol. Both TLS and GSI operate at the transport layer.
They require an ordered reliable transport connection, so typically they are
implemented over Transmission Control Protocol (TCP). This approach is not
suitable for web service-based technologies on the grid. Simple Object
Access Protocol (SOAP) protocol [13] is used by the emerging Open Grid
Service Architecture (OGSA). This necessitates for support message layer
security using XML digital signature standard and the extensible markup
language (XML) encryption standard [14]. Enhancements of SOAP
messaging to provide message integrity and confidentiality are standardized
in Organization for Advancement of Structured Information Standards
(OASIS). The WS-secure conversation specification [15] describes how two
entities can authenticate each other at the message layer. Grid middleware
like Globus Toolkit™ Version 4.0, pyGridWare and Open Grid Services
Infrastructure (OGSI).NET/Web Services Resource Framework (WSRF).NET
(Wasson et al., 2004) use WS-secure conversation based on TLS
authentication handshake in the SOAP message layer. Globus Toolkit [3]
provides security services for authentication, authorization, management of
user credentials and user information.
Wei Jiea et al. [5] have proposed a scalable GIS architecture for information
management in a large scale Grid Virtual Organization (VO) with facilities to
capture resource information for an administrative domain. The framework
also incorporates security policies for authentication and authorization control
of the GIS at both the site and the VO layers. Haibo Chena et al. [6] have
applied trusted computing technologies in order to attain resource
virtualization to ensure behavior conformity and platform virtualization for
operating systems. Yuri Demchenko [7] has analyzed identity management in
VOs and usage of Web Service (WS)-Federation and WS-Security standards.
G. Laccetti and G. Schmid [8] have introduced a unified approach for access
control of grid resources. (PKI) Public Key Infrastructure and (PMI) Privilege
Management Infrastructure infrastructures were utilized at the grid layer after
authentication and authorization procedures. Xukai Zoua et al. [9] have

proposed an elegant Dual-Level Key Management (DLKM) mechanism using
Access Control Polynomial (ACP) and one-way functions. The first level
provided flexible and secure group communication whereas the second level
offered hierarchical access control. Li Hongweia et al. [10] have proposed an
identity-based authentication protocol for grid on the basis of the identity-
based architecture for grid (IBAG) and corresponding encryption and
signature schemes. Being certificate-free, the authentication protocol aligned
well with the demands of grid computing. Yan Zhenga et al [11] use identity-
based signature (IBS) scheme for grid authentication. Hai-yan Wanga. C and
Ru-chuan Wanga [12] have proposed a grid authentication mechanism, which
was on the basis of combined public key (CPK) employing elliptic curve
cryptography (ECC).
Once the grid entities are authenticated, key distribution occurs between the
grid entities to ensure secure communication. Some existing key distribution
schemes include manual key distribution, hierarchal trees and secure lock.
Manual key distribution lacks forward and backward secrecies, whereas
hierarchical model requires more footprints. Secure lock method is
computation intensive. The proposed system encrypts session keys thereby
reducing computational costs, communication costs, and key storage
footprint. Although the method is simple, it ensures good accuracy. The
proposed work aims at authenticating the users and allocating channel
resources to the users based on the availability of the resource and security
weights. It ensures both user and resource authentication. Then encryption
key to ensure secure communication among these members is distributed
among the channel members. The message digest of the information to be
transferred is encrypted for confidentiality using the key and then transferred
to authenticated grid entities.
Reconcilable key management mechanism is proposed by Li [16] in which
the key management middleware in grid can dynamically call the optimum
rekeying algorithm and rekeying interval is based on the rates that the group
members join and leave.
Li [18] proposed an authenticated encryption mechanism for group
communication in term of the basic theories of threshold signature and basic
characteristics of group communication in grid. In this mechanism, each
member in the signing group can verify the identity of the signer, and the
verifying group keeps only private key.
A scalable service scheme for secure group communication using digital
signatures to provide integrity and source authentication is proposed by Li [17]
. In this approach, Huffman binary tree is used to distribute keys in VO and
complete binary tree is used to manage keys in administrative domain. Sudha
[20] proposed to use tree-based approach for secure group key generation
and establishment of communication among domains in a VO using trust
relationships.
The proposed work aims at authenticating the users and allocating channel
resources to the users based on the availability of the resource and security

weights. Then encryption key to ensure secure communication among these
members is distributed among the channel members. Digest of the
information to be transferred is formed and then it is encrypted for
confidentiality and then transferred to its peers. The remaining of the paper is
organized as follows: Section 2 is constituted by the proposed authentication
and channel distribution mechanism. Section 3 discusses about the analysis
done so far. Section 4 discusses about implementation results and Section 5
concludes the paper.
2. PROPOSED SYSTEM ARCHITECTURE
The components of the system depicted in figure 1 are described as follows..
1) Registration component to register the legitimate users/managers of the
channel.
2) Join/leave component to take care of authentication of the channel users.
3) Key generation system that generates the encryption key randomly.
4) Key distribution system that distributes the keys to the authenticated
members of the channel.
5) Channel to distribute the encrypted information among the group members.
When legitimate entities (users and resources) register to the channel, the
encrypted hash value of their passwords is stored in the authentication server.
The proposed approach initially authenticates the user by matching its
encrypted hash value with that stored in the authentication file. If
authenticated, a random key is generated and distributed among the
members in the channel or group. The message digest of the message to be
transferred is encrypted and multicast to the group through the channel.. The
receivers then decrypt and decode to get the original message (figure 2)
Members/
Resources
Manager
Registration
Join/Leave
Authentication
Key Distribution
Key Generation
EncryptionChannel
Authentication
Server
Key distribution

The entire process consists of two major activities – authentication and key
distribution for secure group communication. These activities are described in
the following paragraphs.
2.1. Authentication Process:
The block diagram illustrating the registration process of the users is
depicted in the Figure 3. Users who require services from the VO register
using their username and password. The hash value of the password is
calculated using Message Digest (MD5) algorithm and the encrypted
password is stored in the authentication file.
The user who wants the services of VO has to login using the
username and password. Here, ui and pwi refers to username and
password of ith
user. The Authentication server calculates the hash value of
the password and compares it with the decrypted value maintained in the
authentication file. If the user is a valid user then the authentication server
allows the user to join the channel and distributes the encryption key to the
user.
FIGURE 1: System Architecture
Grid
Entities
Authentication
Server
Controller
key
generation
Channel
register
OK
Authentication
database
Login
Pwd hash/encrypt
Check pwd hash
OK
OK
OK
join
Distribute keys
Distribute keys
Secure group communication
FIGURE 2: Process of secure group communication
Registration
Authentication
Gen Key

FIGURE 3: Authentication Scheme
2.2. Key Distribution And Secure Group Communication:
Confidentiality in information transfer in a distributed system is enabled
by encrypting the information. Keys should be distributed securely among the
members of the group. In existing approaches, each member shares a secret
key with the group controller. If the information is to be transferred to ‘n’
members, ‘n’ encryptions followed by ‘n’ unicasts are needed. The
computational complexity of the existing approach is overcome by using
encoded session keys. Hence the proposed approach uses only an encoding
followed by a multicast operation. This leads to reduced computation and
provides efficient group communication. Further, the proposed approach
ensures dynamic and secure group communication, forward secrecy and
backward secrecy. The encoded key is used to manage member join, leave
operations and for group communication. The security of the communication
is achieved using one-way hash function to maintain integrity and encryption
for confidentiality. Since a key is maintained for each channel/group, secure
group communication is facilitated. The computation time of the key
Choice?
User registers with username
and password in Authentication
file
Authentication file stores the
encrypted value of the password
User
logins
AF calculates MD5 value of the
password
AF authenticates the user
Warns the user
AF Issues Token to the user
Is User
Valid?
Registration Authentication
NO
YES
AF -
Authentication
File

distribution is fast when compared to the key distribution by traditional
algorithms like AES.
MD5 is used to generate the message digest. MD5 verifies data integrity by
creating a 128-bit message digest from a message of arbitrary length. It can
be used for digital signature applications, where a large file must be
compressed in a secure manner before being encrypted using a public-key
system. Steps in MD5 approach is listed as follows.
1) Arbitrary length message is padded with a ‘1’ followed by ‘0’s, so that its
length is congruent to 448, modulo 512.
2) Then the length of the message (64 bits) is appended to it.
3) The MD5 algorithm uses four 32-bit state variables. They are initialized with
constant values. These variables are sliced and diced to form the message
digest.
4) 512-bit message blocks are used to modify the state in 4 rounds. Each
round has 16 similar operations based on a non-linear function F, modular
addition, and left rotation. Function F is different for each round. At the end of
4 rounds, the message digest is formed from the state variables. The
message digest is then encrypted using Data Encryption Standard (DES)
algorithm [19] and transmitted to its peer group member.
3. ANALYSIS
The analysis of the work has been done under the following heads:
3.1. Md5 Analysis:
The probability of two messages having the same message digest is
on the order of 2^64 operations. The probability of coming up with any
message having a given message digest is on the order of 2^128 operations.
This ensures uniqueness of the message digest.
3.2. Replay attack:
Usually replay attack is called as ‘man in the middle’ attack. Adversary
stays in between the user and the file and hacks the user credentials when
the user contacts file. As key matching between the users is checked before
file transfer and the information is encrypted before transfer, the probability of
this attack is minimized.
3.3. Guessing attack:
Guessing attack is nothing but the adversaries just contacts the files by
randomly guessed credentials. The effective possibility to overcome this
attack is to choose the password by maximum possible characters, so that the
probability of guessing the correct password can be reduced. As the proposed
approach uses random generation of key, it is more difficult to guess the
password.
3.4. Stolen-verifier attack:

Instead of storing the original password, the verifier of the password is
stored. As the encrypted hash value of the password is stored, the proposed
protocol is also more robust against the attack.
.
4. RESULTS AND DISCUSSIONS
The
proposed authentication and distribution of channels has been implemented
and tested on Globus middleware. It is tested with five valid and five invalid
users. Each of the five valid users has their own username and password.
Initially, they have created their user account using their username and
password (Table 1). The authentication server stores the encrypted hash
values of the passwords. As the hash values of the passwords are different,
it ensures uniqueness.
Sl. No Username Password Hash value
1 user1 admin 4c56ff4ce4aaf9573aa5dff913df913d
2 user2 Test2 Dfg45f4ce4aaf9573aa5dff913df913e
3 user3 test5 dddd6ffsdfdfdffffff913df997art567fg
4 user4 test8 4c56ff4ce4aaf9573aa5dff913df913d
5 user5 test10 sfggce4aaf9573aa5dff913df913fget
TABLE 1: Authentication File with unique hash value of passwords

0
1
2
3
4
5
6
7
8
9
1 2 3 4 5 6
Number of Nodes
TimeinSec
Channel / Key Distribution Time Join Time
Leave Time Encrypted File Transfer
Users join in the distributed channels across multiple machines in the grid.
Once authenticated, key distribution and secure file transfer takes place.
Figure 4 shows that the key distribution time and time for node join/leave
remains almost a constant, irrespective of the number of nodes, incontrast to
the hierarchical approach. Once the user joins the channel, secure file
transfer occurs by encryption the information and multicasting it to the group
members. Hence file transfer time also remains a constant in contrast to the
unicast approach.
5. CONCLUSION
Grid Computing enables virtual organizations, to share geographically
distributed resources. This paper proposes an effective approach for
authentication and key distribution to ensure secure group communication in
the grid environment. As the interpreted and distinct form of user credentials
are maintained in the authentication files, there is very less chance to reveal
the user credentials to the adversary. The implementation of our
authentication protocol showed its effective performance in pinpointing the
adversaries and paving the way to valid users to access resources in the VO
by establishing as efficient computational channel distribution. Finally it is
worth fit to host this scheme as a service in globus , also this basic scheme
simply reduces computation complexity by replacing cryptographic encryption
and decryption operations. Computation complexity further reduced by using
algorithms like SHA , RIPEMD , IDEA .
FIGURE 4: Experimental Results

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