Serena Pastore
National Institute of Astrophysics, Astronomical Observatory of Padova, vicolo Osservatorio 5, 35122, Padova, Italy
Keywords: Grid Security Infrastructure, Authentication and Authorization.
Abstract: Security in a grid infrastructure is implemented by adopting standard protocols that realize authentication,
authorization and access control to shared distributed network nodes, resources and services. Despite of
middleware used to built a grid, security components provide mutual authentication, delegation and single
sign-on features while every virtual organization joining the grid sets own authorization policies. Access
control and secure communication are the most important aspect of security that need to be addressed if the
shared resources are web services. This paper reports about the strategy required for securing web services
as means of an application packaged as a Web ARchive (WAR) file deployed in a grid node that has to be
shared for grid users. Software implementation uses packages coming from different past and present grid
projects that secure both web container and the application. Security chain is basically implemented by
means of java libraries to provide a message handler technique for digital signing and validating SOAP
message and an authorization engine compatible with methods adopted in grid.
Grid security refers to the need for any Virtual
Organization (VO) which composes the grid
infrastructure, to share information, resources and
even applications across organizational boundaries
in a secure and highly efficient manner (Foster, I. et
al., 2001). The globally distributed feature of a grid
system should allow for all grid entities (users
belonging to a VO, nodes and services)
authentication to be identified in the infrastructure,
secure communication over the network and
authorization to make use of shared objects
according to both local (site level) and distributed
policies (VO level). Enabling remote access to
different network systems and sharing resources
require many other services like mutual
authentication among each parties forming the grid
to prove who they are, single sign-on for user and
delegation to have the necessary permissions to act
on behalf of a grid entity. Access control and secure
communication are the most important aspect of
security that needs to be addressed for sharing web
service application: access control in specific
encompasses a number of concepts that includes
knowing who users are (identity) and what they can
do in the applications (authorization) and keeping
record of what they have done (auditing). Despite
middleware used to built a grid, components which
address security requirements adopt standard
technologies. According the Globus Security
Infrastructure (GSI) ( that is
the reference architecture developed by the Globus
Alliance, the SSL(Secure Sockets Layer) protocol
provides secure communication, authentication is
realized by using digital certificate of the Public Key
Infrastructure(PKI) (http//, while
various authorization models are implemented. GSI
creates a basic security mechanism that does not
require a centralized management authority. Public
key cryptography is used for digitally signing any
piece of information. Each grid entity has an unique
identity composed by a signed certificate following
the X.509 format and a private key (credentials)
which authenticate it in grid. A Certification
Authority (CA) guarantees identities by issuing
signed certificates that validate individuals and
organizations: in a global grid environment with
many parties involved, each CA is structured to form
a hierarchy of trusted entities. Delegation and
mutual authentication services are provided to grid
by a proxy method. This introduces new temporary
credentials (a certificate signed by the owner from
the original one and a private key with a limited
lifetimes) that can be passed to any grid resource.
Authorization indeed outlines the core problem in
Pastore S. (2006).
In Proceedings of WEBIST 2006 - Second International Conference on Web Information Systems and Technologies - Internet Technology / Web
Interface and Applications, pages 264-267
DOI: 10.5220/0001252802640267
grid setting that is how to handle and combine the
overlay of polices imposed by different
organizations. A first method uses a global-to-local
identity mapping by a special authorization file
grid-mapfile. A LDAP directory stores the
list of certificates corresponding to users affiliated to
VOs and this information is used to create a file that
contains mappings from the user identity to a local
user account (real or pool). The file, distributed in all
grid nodes and frequently updated, is checked
whenever a host receives a request addressing a
service or resource that needs authorization. Other
solutions leave access control decisions to each
organization composing the system. An example is
the Virtual Organization Membership Service
(VOMS) method (Alfieri R. et al., 2005) for central
users management at VO level. The approach allows
to catalogue each users on adhering on groups, roles
and capabilities mapping identities with roles.
Sharing web services application for a VO in a grid
site offers many integration advantages, but presents
security challenges: it should be only accessed by
identified users according security policies locally
implemented. The paper looks at the strategy of
securing web services application to be shared in a
specific grid environment like the Italian INFN
production grid ( The case
study refers to apply control access rules to java web
services deployed as Web ARchive (WAR) file
whose security process makes use of software
developed in grid projects.
The reference grid infrastructure (http://grid- consists of several VOs representing
different institutes: each one contributes with
distributed grid nodes to provide resources and
services. The testbed is built on a specific grid
middleware (INFN-GRID) that gathers many
software developed in past and present grid projects
running on Linux platforms. Among these, Globus
Toolkit (GT) developed by Globus Alliance
(, EDG software of DataGrid
project (, LCG
middleware provided by CERN (http://eu- and gLite toolkit
of EGEE project ( are the
mainly used. They implement many grid features by
means of modules installed on grid nodes. The
resulting architecture
( outlines
logical machine types specifically named to
represent single functionalities that VOs share in
grid. Each site contributes with at least Computing
Element (CE) that is a frontend node defined as a
batch queue system built on a homogenous a farm of
computing nodes (Worker Nodes) behind it and
Storage Element (SE) that provides uniform access
to storage spaces. Grid gateway allowing for
command line interface to grid operations is usually
the User Interface (UI) machine even if grid portal
are also available. Specialized sites provide
management features like the information service
that keeps updated information about distributed
resources and the workload management system that
is responsible of match-making between best
resources and job requirements and the scheduling
and processing of the job itself. In this testbed both
users, hosts and services must possess valid
identities released by a trusted CA: the INFN
institute manages a CA organized in a set
Registration Authorities (RAs) to locally delegate
the identification.
The trusted CAs root certificates as well as the
certificate revocation lists (CRLs) are available in
rpm formats and installed in grid machines (in the
/etc/grid-security directory),where credentials
of grid entities that share servers or services are also
stored with the proper permissions. Grid credentials
are kept in a specific UI directory (the
directory) or in the browser. On demand services use
delegated credentials from either the system or user.
Identities are centrally managed by LDAP directory
or relational database: the VO structure (each user
registers to at least one VO) has brought to the
VOMS client-server system for users certificates
management and attributes-based authorization.
Digital certificates are used for authentication, but
also for single sign-on and delegation services: the
proxy mechanism enable the creation, on behalf of
the client, of a short term proxy certificate that will
be used during a session for all subsequent
Figure 1: Distribution of grid entities certificates: creation
of a VOMS proxy certificate and information attached to
interactions with the grid. A specific proxy
certificate that includes VOMS extensions is created
with the command
voms-proxy-init (figure 1).
Globus proxy certificates differ from standard
proposed simply adding the prefix “
CN=proxy” to
the subject DN: VOMS extensions that contain user
authorization information extracted by the VOMS
server are simply included in it and may be passed
directly or delegated remotely to grid services which
extract it for checking. Securing web services in this
infrastructure is a system-wide concern: transport
security (SSL) or message security (SOAP security)
together with secure single sign-on play a part in
providing protection against unauthorized access.
Transport security realizes privacy and data integrity
as well authentication of the communication end
points (HTTPS), message security focuses on
confidentiality (content protection) and integrity
(avoiding modification). Moreover web services are
deployed in specific SOAP engine that supports the
idea of message handler means SOAP messages pass
through a series of processing steps prior to actually
delivering the message to the service
implementation code. Security constraints applicable
to secure web services could be addressed in grid by
using the Trust Manager and Authorization
Framework implemented by middleware packages
named respectively
and edg-java-security.
The approach described to provide secure web
services in grid is applied to a case study of a grid
application that offers facilities over distributed
astronomical databases (Pastore et al., 2004) even if
the security process could be generally applied.
From a technical perspective a web service is a
collection of related operations described by service
description (XML) and network accessible through
XML messaging (SOAP protocol). The application
is structured as a set of java web services processed
by the Axis SOAP engine and deployed in Tomcat 5
web application container running on a digitally
certified CE element: access to services is enabled
for authenticated grid users with specific
authorization rules both by submitting a job from a
UI and using graphical mode (i.e. web pages
developed in JSP technology). The overall security
process (figure 2) which every incoming request to
web services is subjected to, can be divided into
authentication and authorization steps. The client
SOAP request containing the certificate is send to
the HTTP listener. The authentication phase deals
with the verification of the client identity through
validation of X.509 certificate paths, and is
performed by a gLite module known as Trust
Figure 2: Modules schema for processing secure web
services and description of a policy applied.
The authorization step should check the mapping
between user credentials and access role and is done
by an EDG module called Authorization
Framework. This includes the insertion of an handler
in front of the web service to be protected and the
instantiation of an authorization engine
(Authorization Manager) that along with an optional
user management interface, it allows or denies
access following the policy specified. The engine is
in fact organized as a collection of Policies, one for
each service that needs protection.
3.1 Trust Manager and
Authorization Framework
The Trust Manager, overriding the standard Tomcat
implementation, provides a java implementation of
SSL protocol to support Globus proxy certificates
format and CRLs of CAs. Enabling server-side-only
SSL on the Web service platform, ensures messages
protection in the interaction but with the limitation
of securing a single communication channel. After
that the client request is verified for authorization
step, before passing on to the actual service
implementation. The signed SOAP request is
intercepted and submitted through an Axis handler
implemented as a java class that protects the web
service implementation. The handler examines the
request, extracts the client certificate and all
information embedded (i.e. subject DN and
attributes), communicates with one instance of the
Authorization Manager to whom delegates any
decision and gets back the result of the step to access
or deny the service. The policy (figure 2) applied to
web service is defined in a XML configuration file
AuthzManager.xml) to perform a two-step
mapping between the client (its DN) and a given role
and (optionally) between such attribute and a local-
ID value usable by an application. These phases are
specified into distinct sections: AttributeRepository
and TranslationMap. Both define attribute types
where to find the information needed to the
authorization process. For example in the VOMS
management, the
voms type defines the use of
VOMS extensions for checking rules. Otherwise the
second mapping always gets the information from
pluggable storage module (
AttributeMap) that
stores associations in a memory map and in turn
specifies their behaviour (i.e.
regex value allows
for keys specification as regular expressions).
3.2 Practical Steps for Access Secure
Web Services Implementation
The full process requires the installation and
configuration of the java environment, related
libraries (i.e. cryptographic libraries) and other tools
(i.e. logging services) together with digital
certificates for CAs and hosts involved. Client
interaction with web service requires the installation
of users digital credentials. Both
security-trustmanager and edg-java-
security provide client and server java libraries to
be used in applications. Trust Manager software
gives configuration files and scripts to modify
standard Tomcat 5 configuration and interact with it
through the secure connection (8443 port) validated
by host credentials. Web services deployment
usually means the availability of the application as a
single Web ARchive (WAR) file: the security
process setup requires the settings of the modules
and libraries and files inclusions before the
automatic packaging made with Ant tools. Java
libraries for server authentication and authorization
should be available in the specific library application
directory as well as the Axis ones. The configuration
of the Authorization Framework requires the setup
of the manager file to specify authorization policy
applied, the registration of the Axis Handler with the
service itself in the service deployment descriptor
server-config.wsdd) and the definition of
handler parameters (i.e. log4j configuration file,
location of the manager file, default policy, etc.) in a
text file (called
whose location is specified in the web application
descriptor (
web.xml). Once deployed in the
container, every client java application accesses the
secure web service by using authentication and
authorization libraries.
Strategy for securing web service application to be
shared in grid environment as WAR file, addresses
secure communication and access control.
Implementation of security constraints are realized
by using specific grid software. Trust Manager (by
gLite) provides digital authentication supporting
proxy methods. Authorization Framework (by EDG)
realizes the authorization process required to access
control to web services by means of a message
handler technique to validating messages and an
authorization engine that describing policy in XML
format is compatible with the VOMS system used
for VO level managing. This allows for setting
specific access role for such shared resources based
on VOMS attributes. Despite of software
implementation, the security design is applicable for
every java web services. Moreover the use of XML
technologies allows to increase security by applying
in future development web services security-focused
specifications introduced by WS-Security, XML
signatures or XML encryption standards.
Foster, I. et al 2001. The Anatomy of the Grid: Enabling
Scalable Virtual Organizations. In Journal
Supercomputer Applications, 15(3).
The Globus Security Infrastructure (GSI) of the Globus
Toolkit. At URL:
Public-Key Infrastructure (X.509). At url:
Alfieri, R. et. al, 2005. From gridmap-file to VOMS:
managing authorization in a Grid environment. In
Future Generation Computer System 21 549-558.
Italian National Institute of Nuclear Physics (INFN) grid
infrastructure. At url:
LCG middleware (at url: for
the LHC (Large Hadron Collider) projects
European DataGrid (EDG) project (at url: http://eu-
gLite (at url: software for the
Enabling Grids for E-sciencE (EGEE) project (at url:
DataGrid Software Architecture Models, 2004. At URL:
Pastore, et al., 2004. Enabling Access to astronomical
databases through the grid: a case study. In Proc. of
Astronomical Data Analysis III Conference.