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Chapter 3

Separation

Cyber Attacks

Protecting National Infrastructure, 1st ed.

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Using a firewall to separate network assets from intruders is the most familiar approach in cyber security
Networks and systems associated with national infrastructure assets tend to be too complex for firewalls to be effective

Chapter 3 – Separation

Introduction

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Three new approaches to the use of firewalls are necessary to achieve optimal separation
Network-based separation
Internal separation
Tailored separation

Chapter 3 – Separation

Introduction

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Fig. 3.1 – Firewalls in simple and complex networks

Chapter 3 – Separation

Separation is a technique that accomplishes one of the following
Adversary separation
Component distribution

Chapter 3 – Separation

What Is Separation?

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

A working taxonomy of separation techniques: Three primary factors involved in the use of separation
The source of the threat
The target of the security control
The approach used in the security control

(See figure 3.2)

Chapter 3 – Separation

What Is Separation?

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Chapter 3 – Separation

Fig. 3.2 – Taxonomy of separation techniques

Separation is commonly achieved using an access control mechanism with requisite authentication and identity management
An access policy identifies desired allowances for users requesting to perform actions on system entities
Two approaches
Distributed responsibility
Centralized control
(Both will be required)

Chapter 3 – Separation

Functional Separation?

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Chapter 3 – Separation

Fig. 3.3 – Distributed versus centralized mediation

Firewalls are placed between a system or enterprise and an un-trusted network (say, the Internet)
Two possibilities arise
Coverage: The firewall might not cover all paths
Accuracy: The firewall may be forced to allow access that inadvertently opens access to other protected assets

Chapter 3 – Separation

National Infrastructure Firewalls

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Chapter 3 – Separation

Fig. 3.4 – Wide area firewall aggregation and local area firewall segregation

Increased wireless connectivity is a major challenge to national infrastructure security
Network service providers offer advantages to centralized security
Vantage point: Network service providers can see a lot
Operations: Network providers have operational capacity to keep security software current
Investment: Network service providers have the financial wherewithal and motivation to invest in security

Chapter 3 – Separation

National Infrastructure Firewalls

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Chapter 3 – Separation

Fig. 3.5 – Carrier-centric network-based firewall

Network-based firewall concept includes device for throttling distributed denial of service (DDOS) attacks
Called a DDOS filter
Modern DDOS attacks take into account a more advanced filtering system

Chapter 3 – Separation

DDOS Filtering

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Chapter 3 – Separation

Fig. 3.6 – DDOS filtering of inbound attacks on target assets

SCADA – Supervisory control and data acquisition
SCADA systems – A set of software, computer, and networks that provide remote coordination of control system for tangible infrastructures
Structure includes the following
Human-machine interface (HMI)
Master terminal unit (MTU)
Remote terminal unit (RTU)
Field control systems

Chapter 3 – Separation

SCADA Separation Architecture

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Chapter 3 – Separation

Fig. 3.7 – Recommended SCADA system firewall architecture

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 arise
Basic principles for truly air-gapped networks:
Clear policy
Boundary scanning
Violation consequences
Reasonable alternatives

Chapter 3 – Separation

Physical Separation

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Chapter 3 – Separation

Fig. 3.8 – Bridging an isolated network via a dual-homing user

Hard to defend against a determined insider
Threats may also come from trusted partners
Background checks are a start
Techniques for countering insider attack
Internal firewalls
Deceptive honey pots
Enforcement of data markings
Data leakage protection (DLP) systems
Segregation of duties offers another layer of protection

Chapter 3 – Separation

Insider Separation

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Chapter 3 – Separation

Fig. 3.9 – Decomposing work functions for segregation of duty

Involves the distribution, replication, decomposition, or segregation of national assets
Distribution: creating functionality using multiple cooperating components that work together as distributed system
Replication: copying assets across components so if one asset is broken, the copy will be available
Decomposition: breaking complex assets into individual components so an isolated compromise won’t bring down asset
Segregation: separation of assets through special access controls, data markings, and policy enforcement

Chapter 3 – Separation

Asset Separation

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Chapter 3 – Separation

Fig. 3.10 – Reducing DDOS risk through CDN-hosted content

Typically, mandatory access controls and audit trail hooks were embedded into the underlying operating system kernel
Popular in the 1980s and 1990s

Chapter 3 – Separation

Multilevel Security (MLS)

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer

Chapter 3 – Separation

Fig. 3.11 – Using MLS logical separation to protect assets

Internet separation: Certain assets simply shouldn’t be accessible from the Internet
Network-based firewalls: These should be managed by a centralized group
DDOS protection: All assets should have protection in place before an attack
Internal separation: Critical national infrastructure settings need an incentive to implement internal separation policy
Tailoring requirements: Vendors should be incentivized to build tailored systems such as firewalls for special SCADA environments

Chapter 3 – Separation

National Separation Program

The University of Adelaide, School of Computer Science

Chapter 2 — Instructions: Language of the Computer