Copyright © 2012, Elsevier Inc. All Rights ReservedCh.docx

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Copyright © 2012, Elsevier Inc. All Rights Reserved
Chapter 3
Separation
Cyber Attacks
Protecting National Infrastructure, 1st ed.
Copyright © 2012, Elsevier Inc. All Rights Reserved
The University of Adelaide, School of Computer Science
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Chapter 2 — Instructions: Language of the Computer
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Using a firewall to separate network assets from intruders is the
most familiar approach in cyber securityNetworks and systems
associated with national infrastructure assets tend to be too
complex for firewalls to be effective
Copyright © 2012, Elsevier Inc. All rights Reserved
Chapter 3 – Separation
Introduction

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Three new approaches to the use of firewalls are necessary to
achieve optimal separationNetwork-based separationInternal
separationTailored separation
Introduction
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Fig. 3.1 – Firewalls in simple and complex networks

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Separation is a technique that accomplishes one of the
followingAdversary separationComponent distribution
What Is Separation?
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A working taxonomy of separation techniques: Three primary
factors involved in the use of separationThe source of the
threatThe target of the security controlThe approach used in the
security control
(See figure 3.2)
What Is Separation?
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Fig. 3.2 – Taxonomy of separation techniques
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Separation is commonly achieved using an access control
mechanism with requisite authentication and identity
managementAn access policy identifies desired allowances for
users requesting to perform actions on system entitiesTwo
approachesDistributed responsibilityCentralized control(Both
will be required)
Functional Separation?
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Fig. 3.3 – Distributed versus centralized mediation
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Firewalls are placed between a system or enterprise and an un-
trusted network (say, the Internet)Two possibilities
ariseCoverage: The firewall might not cover all pathsAccuracy:
The firewall may be forced to allow access that inadvertently
opens access to other protected assets
National Infrastructure Firewalls
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Fig. 3.4 – Wide area firewall aggregation and local area firewall
segregation
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Increased wireless connectivity is a major challenge to national
infrastructure securityNetwork service providers offer
advantages to centralized securityVantage point: Network
service providers can see a lotOperations: Network providers

have operational capacity to keep security software
currentInvestment: Network service providers have the financial
wherewithal and motivation to invest in security
National Infrastructure Firewalls
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Fig. 3.5 – Carrier-centric network-based firewall
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Network-based firewall concept includes device for throttling
distributed denial of service (DDOS) attacksCalled a DDOS
filterModern DDOS attacks take into account a more advanced
filtering system
DDOS Filtering

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Fig. 3.6 – DDOS filtering of inbound attacks on target assets
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SCADA – Supervisory control and data acquisitionSCADA
systems – A set of software, computer, and networks that
provide remote coordination of control system for tangible
infrastructuresStructure includes the followingHuman-machine
interface (HMI)Master terminal unit (MTU)Remote terminal
unit (RTU)Field control systems
SCADA Separation Architecture
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Fig. 3.7 – Recommended SCADA system firewall architecture
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Why not simply unplug a system’s external connections?
(Called air gapping)As systems and networks grow more
complex, it becomes more likely that unknown or unauthorized
external connections will ariseBasic principles for truly air-
gapped networks:Clear policyBoundary scanningViolation
consequencesReasonable alternatives
Physical Separation
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Fig. 3.8 – Bridging an isolated network via a dual-homing user
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Hard to defend against a determined insiderThreats may also

come from trusted partnersBackground checks are a
startTechniques for countering insider attackInternal
firewallsDeceptive honey potsEnforcement of data
markingsData leakage protection (DLP) systemsSegregation of
duties offers another layer of protection
Insider Separation
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Fig. 3.9 – Decomposing work functions for segregation of duty
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Involves the distribution, replication, decomposition, or
segregation of national assetsDistribution: creating
functionality using multiple cooperating components that work
together as distributed systemReplication: copying assets across
components so if one asset is broken, the copy will be
availableDecomposition: breaking complex assets into
individual components so an isolated compromise won’t bring
down assetSegregation: separation of assets through special
access controls, data markings, and policy enforcement

Asset Separation
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Fig. 3.10 – Reducing DDOS risk through CDN-hosted content
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Typically, mandatory access controls and audit trail hooks were
embedded into the underlying operating system kernelPopular in
the 1980s and 1990s
Multilevel Security (MLS)
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Fig. 3.11 – Using MLS logical separation to protect assets
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Internet separation: Certain assets simply shouldn’t be
accessible from the InternetNetwork-based firewalls: These
should be managed by a centralized groupDDOS protection: All
assets should have protection in place before an attackInternal
separation: Critical national infrastructure settings need an
incentive to implement internal separation policyTailoring
requirements: Vendors should be incentivized to build tailored
systems such as firewalls for special SCADA environments
National Separation Program
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