JOURNAL OF COMMUNICATIONS AND NETWORKS, VOL. 14, NO. 6, DECEMBER 2012 597
Wide-Area SCADA System with Distributed Security
Framework
Yang Zhang and Jun-Liang Chen
Abstract: With the smart grid coming near, wide-area supervisory
control and data acquisition (SCADA) becomes more and more
important. However, traditional SCADA systems are not suitable
for the openness and distribution requirements of smart grid. Dis-
tributed SCADA services should be openly composable and secure.
Event-driven methodology makes service collaborations more real-
time and flexible because of the space, time and control decoupling
of event producer and consumer, which gives us an appropriate
foundation. Our SCADA services are constructed and integrated
based on distributed events in this paper. Unfortunately, an event-
driven SCADA service does not know who consumes its events, and
consumers do not know who produces the events either. In this
environment, a SCADA service cannot directly control access be-
cause of anonymous and multicast interactions. In this paper, a
distributed security framework is proposed to protect not only ser-
vice operations but also data contents in smart grid environments.
Finally, a security implementation scheme is given for SCADA ser-
vices.
Index Terms: Access control, event-driven service, service col-
laboration, smart grid, supervisory control and data acquisition
(SCADA).
I. INTRODUCTION
The smart grid can be viewed as an evolutionary electric sys-
tem with more efficiency, which uses information and secure
communication technologies, and co mputational intelligence in
an integrated fashion from the generator to the end consumers of
the electricity. The integration philosophy requires the informa-
tion system in the smart grid should b e decoupling, composable
and open. Traditional supervisory control and data acquisition
systems (SCADA) are designed to be close and act as the brain
of the power grid, which consist of one or more remote termi-
nal units (RTU) connected to a variety of sensors and actuators,
and some master stations. When the smart grid comes near, the
SCADA system should also become open and distributed, and
can interact with more and more other services without side ef-
fects. Distributed event-based systems (DEBS) [1], [2] can act
as the infrastructure for SCADA services to collaborate in wide
area.
Manuscript receiv e d April 29, 2012.
This work has been supported by 973 program of National Basic Research
Program of China (Grant No. 2011CB302704, 2012CB315802). National Nat-
ural Science Foundation of China (Grant No. 61001118, 61171102, 61003067,
61132001); Program for Ne w Century Excellent Talents in University (Grant
No. NECT-11-0592); Project of New Generation Broadband Wireless Network
under Grant (Grant No. 2012ZX03005008-001).
The authors are with the State Key laboratory of Networking and Switch-
ing Technology, Beijing University of Posts and Telecommunications, email:
{YangZhang, chjl}@bupt.edu.cn.
Digital Object Identifier 10.1109/JCN.2012.00025
During SCADA services collaborating in wide area, events
are the basic mechanism. First, event subscribers, i.e., some
distributed services as clients, express their interest in receiv-
ing certain events in the form of a n event subscription. Then,
event publishers, i.e., other distributed services as servers, pub-
lish events which will b e delivered to all interested event sub-
scribers. A subscriber is usually indifferent to which particular
publishers supply the events that it is interested in. Similarly,
a publisher does not need to know about the set of subscribers
who will receive a published event. As an academic effort, the
work in [3] proposed an approach to transform a centrally or-
chestrated business process into distributed event-driven collab-
orating services. As industrial efforts, wireless sensor network
(WSN) [4] and web service eventing (WS-Eventing) [5] were
proposed as standard specifications for web services to use the
event publish/subscribe mechanism as an interaction way.
When the critical SCADA services are deployed on the Inter-
net, they may a lso create many new vulnerabilities if they are not
equipped with the appropriate security controls. Providing secu-
rity for such complex open systems may seem an unfathomable
task. We may leave utilities ope n to cybe r a ttacks. Furthermore,
for event-driven SCADA services, the consumers do not directly
get events from them and they cannot directly reject them to ac-
cess to their events. The underpinning notification bro ker (NB)
network in DEBS assumes the final delivery of events. So, it is
possible to integrate some NBs to help control security. In addi-
tion, one event is subscribed by many consumers and different
consumers possibly receive the events from different NBs. We
need many distributed NBs collaborate to help one SCADA ser-
vice complete security control.
The contribution of this paper is three-fold:
1. A wide-area SCADA system is constructed b ased on event-
driven SCADA services, where other services can collaborate
with them through the DEBS infrastructure.
2. A secure framework is proposed. The notification brokers at
the edge of a DEBS are used to be delegated some enforce-
ment of polices such that distributed security control can be
flexibly realized in smart grid environments.
3. Based on the homomorphic key-switching scheme, an imple-
mentation scheme for the secure framework is proposed. We
give an approach to integrate encryption operations into the
access control model with supporting attribute separation.
II. PRELIMINARIES
A. Event-Driven SCADA Service Communication Infrastruc-
ture
An event-driven SCADA service communication infrastruc-
ture (generally referred to DEBS) is composed of a set of
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