Wireless Security: Know It All by Praphul Chandra, Dan Bensky, Tony Bradley, Chris Hurley | | NOOK Book (eBook) | Barnes & Noble
Wireless Security: Know It All

Wireless Security: Know It All

by Praphul Chandra, Dan Bensky, Tony Bradley, Chris Hurley

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The Newnes Know It All Series takes the best of what our authors have written to create hard-working desk references that will be an engineer's first port of call for key information, design techniques and rules of thumb. Guaranteed not to gather dust on a shelf!

Communications engineers need to master a wide area of topics to excel. The Wireless Security


The Newnes Know It All Series takes the best of what our authors have written to create hard-working desk references that will be an engineer's first port of call for key information, design techniques and rules of thumb. Guaranteed not to gather dust on a shelf!

Communications engineers need to master a wide area of topics to excel. The Wireless Security Know It All covers every angle including Emerging Wireless Technologies and Security Issues, Wireless LAN and MAN Security, as well as Wireless Personal Area Networks.

• A 360-degree view from our best-selling authors
• Topics include Today’s Wireless Technology, Security Definitions and Concepts, and Wireless Handheld devices
• The ultimate hard-working desk reference; all the essential information, techniques and tricks of the trade in one volume

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Elsevier Science
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Newnes Know It All
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Wireless Security

By Praphul Chandra Alan Bensky Tony Bradley Chris Hurley Steve Rackley John Rittinghouse James F. Ransome Timothy Stapko George L. Stefanek Frank Thornton Jon Wilson


Copyright © 2009 Elsevier Inc.
All right reserved.

ISBN: 978-0-08-094967-3

Chapter One

Wireless Fundamentals

Praphul Chandra James F. Ransome John Rittinghouse

What is it that makes a wireless medium so unique? What are the problems of operating in the wireless medium and how are they overcome? What are the different types of wireless networks in use today? How does each one of them work and how do they differ from each other? The aim of this chapter is to answer these questions so as to establish a context in which wireless security can be studied in the following chapters.

The first successful commercial use of wireless telecommunication was the deployment of cellular phones (mobile phones). In this book, we refer to these networks as traditional wireless networks (TWNs). These networks were designed with the aim of extending the existing wired public switched telephone network (PSTN) to include a large number of mobile nodes. The deployment of TWNs allowed users to be mobile and still make voice calls to any (fixed or mobile) phone in the world. In other words, TWNs were designed as a wide area network (WAN) technology enabling voice communication. These networks have evolved over time to support both voice and data communication but the underlying feature of the TWNs being a WAN technology is still true.

For a long time, TWNs were the predominant example of wireless telecommunication. In the late 1990s, another wireless technology emerged: wireless local area networks (WLANs). Unlike TWNs, WLANs were designed primarily with the aim of enabling data communication in a limited geographical area (local area network). Though this aim may seem counterintuitive at first (why limit the geographical coverage of a network?), this principle becomes easier to understand when we think of WLANs as a wireless Ethernet technology. Just as Ethernet (IEEE 802.3) provides the backbone of wired local area networks (LANs) today, IEEE 802.11 provides the backbone of wireless LANs.

Just as TWNs were initially designed for voice and over time evolved to support data, WLANs were initially designed for data and are now evolving to support voice.

Probably the most prominent difference between the two standards is that the former is a WAN technology and the latter is a LAN technology. TWNs and WLANs are today the two most dominant wireless telecommunication technologies in the world. Analysts are predicting the convergence (and co-existence) of the two networks in the near future.

Finally, we are today seeing the emergence of wireless mobile ad-hoc networks (MANETs). Even though this technology is still in an early phase, it promises to have significant commercial applications. As the name suggests, MANETs are designed with the aim of providing ad hoc communication. Such networks are characterized by the absence of any infrastructure and are formed on an as-needed (ad hoc) basis when wireless nodes come together within each others' radio transmission range.

We begin by looking at some of the challenges of the wireless medium.

1.1 The Wireless Medium

1.1.1 Radio Propagation Effects

The wireless medium is a harsh medium for signal propagation. Signals undergo a variety of alterations as they traverse the wireless medium. Some of these changes are due to the distance between the transmitter and the receiver, others are due to the physical environment of the propagation path and yet others are due to the relative movement between the transmitter and the receiver. We look at some of the most important effects in this section.

Attenuation refers to the drop in signal strength as the signal propagates in any medium. All electromagnetic waves suffer from attenuation. For radio waves, if r is the distance of the receiver from the transmitter, the signal attenuation is typically modeled as 1/r2 at short distances and 1/r4 at longer distances; in other words, the strength of the signal decreases as the square of the distance from the transmitter when the receiver is "near" the transmitter and as the fourth power when the receiver is "far away" from the transmitter. The threshold value of r where distances go from being "near" to being "far away" is referred to as the reference distance. It is important to emphasize that this is radio modeling we are talking about. Such models are used for simulation and analysis. Real-life radio propagation is much harsher and the signal strength and quality at any given point depends on a lot of other factors too.

Attenuation of signal strength predicts the average signal strength at a given distance from the transmitter. However, the instantaneous signal strength at a given distance has to take into account many other effects. One of the most important considerations that determine the instantaneous signal strength is, not surprisingly, the operating environment. For example, rural areas with smooth and uniform terrain are much more conductive to radio waves than the much more uneven (think tall buildings) and varying (moving automobiles, people and so on) urban environment. The effect of the operating environment on radio propagation is referred to as shadow fading (slow fading). The term refers to changes in the signal strength occurring due to changes in the operating environment. As an example, consider a receiver operating in an urban environment. The path from the transmitter to the sender may change drastically as the receiver moves over a range of tens of meters. This can happen if, for example, the receiver's movement resulted in the removal (or introduction) of an obstruction (a tall building perhaps) in the path between the transmitter and the receiver. Shadow fading causes the instantaneous received signal strength to be lesser than (or greater than) the average received signal strength.

Another propagation effect that strongly affects radio propagation is Raleigh fading (fast fading). Unlike slow fading which effects radio propagation when the distance between the transmitter and the receiver changes of the order of tens of meters, fast fading describes the changes in signal strength due to the relative motion of the order of a few centimeters. To understand how such a small change in the relative distance may affect the quality of the signal, realize that radio waves (like other waves) undergo wave phenomena like diffraction and interference. In an urban environment like the one shown in Figure 1.1a, these phenomena lead to multipath effects; in other words, a signal from the transmitter may reach the receiver from multiple paths. These multiple signals then interfere with each other at the receiver. Since this interference can be either constructive or destructive, these signals may either reinforce each other or cancel each other out. Whether the interference is constructive or destructive depends on the path length (length the signal has traveled) and a small change in the path length can change the interference from a constructive to a destructive one (or vice versa). Thus, if either of the transmitter or the receiver move even a few centimeters, relative to each other, this changes the interference pattern of the various waves arriving at the receiver from different paths. This means that a constructive interference pattern may be replaced by a destructive one (or vice versa) if the receiver moves by as much as a few centimeters. This fading is a severe challenge in the wireless medium since it implies that even when the average signal strength at the receiver is high there are instances when the signal strength may drop dramatically.

Another effect of multipath is inter-symbol interference. Since the multiple paths that the signal takes between the transmitter and the receiver have different path lengths, this means that the arrival times between the multiple signals traveling on the multiple paths can be of the order of tens of microseconds. If the path difference exceeds 1-bit (symbol) period, symbols may interfere with each other and this can result in severe distortion of the received signal.

1.1.2 Hidden Terminal Problem

Wireless is a medium that must be shared by all terminals that wish to use it in a given geographical region. Also, wireless is inherently a broadcast medium since radio transmission cannot be "contained." These two factors create what is famously known as the hidden terminal problem in the wireless medium. Figure 1.1b demonstrates this problem.

Figure 1.1b shows three wireless terminals: A, B and C. The radio transmission range of each terminal is shown by a circle around the terminal. As is clear, terminal B lies within the radio transmission range of both terminals A and C. Consider now what happens if both A and C want to communicate with B. Most media access rules for a shared medium require that before starting transmission, a terminal "senses" the medium to ensure that the medium is idle and therefore available for transmission. In our case, assume that A is already transmitting data to B. Now, C also wishes to send data to B. Before beginning transmission, it senses the medium and finds it idle since it is beyond the transmission range of A. It therefore begins transmission to B, thus leading to collision with A's transmission when the signals reach B. This problem is known as the hidden terminal problem since, in effect, A and C are hidden from each other in terms of radio detection range.

1.1.3 Exposed Terminal Problem

The exposed terminal problem is at the opposite end of the spectrum from the hidden terminal problem. To understand this problem, consider the four nodes in Figure 1.1c.

In this example, consider what happens when B wants to send data to A and C wants to send data to D. As is obvious, both communications can go on simultaneously since they do not interfere with each other. However, the carrier sensing mechanism raises a false alarm in this case. Suppose B is already sending data to A. If C wishes to start sending data to D, before beginning it senses the medium and finds it busy (due to B's ongoing transmission). Therefore C delays its transmission unnecessarily. This is the exposed terminal problem.

1.1.4 Bandwidth

"The Queen is dead. Long Live the Queen."

Bandwidth is one of the most important and one of the most confusing topics in telecommunications today. If you keep up to date with the telecommunication news, you would have come across conflicting reports regarding bandwidth. There are a lot of people claiming "bandwidth is cheap" and probably as many people claiming "it is extremely important to conserve bandwidth." So, what's the deal? Do networks today have enough bandwidth or not?

The problem is there is no single correct answer to that. The answer depends on where you are in the network. Consider the core of the IP and the PSTN networks: the two most widely deployed networks today. The bandwidth available at the core of these networks is much more than required: bandwidth therefore is cheap at the core of the network. Similarly the dawn of 100 Mbps and Gigabit Ethernet has made bandwidth cheap even in the access network (the part of the network that connects the end-user to the core). The wireless medium, however, is a little different and follows a simple rule: bandwidth is always expensive. This stems from the fact that in almost all countries the wireless spectrum is controlled by the government. Only certain bands of this spectrum are allowed for commercial use, thus making bandwidth costly in the wireless world. All protocols designed for the wireless medium therefore revolve around this central constraint.


Excerpted from Wireless Security by Praphul Chandra Alan Bensky Tony Bradley Chris Hurley Steve Rackley John Rittinghouse James F. Ransome Timothy Stapko George L. Stefanek Frank Thornton Jon Wilson Copyright © 2009 by Elsevier Inc. . Excerpted by permission of Newnes. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Meet the Author

Alan Bensky, MScEE, an electronics engineering consultant with over 25 years of experience in analog and digital design, management, and marketing. Specializing in wireless circuits and systems, Bensky has carried out projects for varied military and consumer applications. He is the author of Short-range Wireless Communication, Second Edition, published by Elsevier, 2004, and has written several articles in international and local publications. He has taught courses and gives lectures on radio engineering topics. Bensky is a senior member of IEEE.
Tony Bradley (CISSP-ISSAP) is the Guide for the Internet/Network Security site on About.com, a part of The New York Times Company. He has written for a variety of other Web sites and publications, including BizTech Magazine, PC World, SearchSecurity.com, WindowsNetworking.com, Smart Computing magazine, and Information Security magazine.
Tony is a CISSP (Certified Information Systems Security Professional) and ISSAP (Information Systems Security Architecture Professional). He is Microsoft Certified as an MCSE (Microsoft Certified Systems Engineer) and MCSA (Microsoft Certified Systems Administrator) in Windows 2000 and an MCP (Microsoft Certified Professional) in Windows NT. Tony is recognized by Microsoft as an MVP (Most Valuable Professional) in Windows security.
On his About.com site, Tony has on average over 600,000 page views per month and over 30,000 subscribers to his weekly newsletter. Tony was also author of Essential Computer Security: Everyone’s Guide to E-mail, Internet, and Wireless Security (ISBN: 1597491144).
Chris Hurley is a Senior Penetration Tester in the Washington, DC area. He has more than 10 years of experience performing penetration testing, vulnerability assessments, and general INFOSEC grunt work. He is the founder of the WorldWide WarDrive, a four-year project to assess the security posture of wireless networks deployed throughout the world. Chris was also the original organizer of the DEF CON WarDriving contest. He is the lead author of WarDriving: Drive, Detect, Defend (Syngress Publishing, ISBN: 19318360305). He has contributed to several other Syngress publications, including Penetration Tester's Open Source Toolkit (ISBN: 1-5974490210), Stealing the Network: How to Own an Identity (ISBN: 1597490067), InfoSec Career Hacking (ISBN: 1597490113), and OS X for Hackers at Heart (ISBN: 1597490407). He has a BS from Angelo State University in Computer Science and a whole bunch of certifications to make himself feel important.
Stephen A. Rackley holds a Doctorate in Experimental Physics at the Cavendish Laboratory, University of Cambridge. He has worked for 26 years in the energy industry, with experience in some of the main technologies that are key to the currently most mature CO2 storage option - identification, assessment, monitoring and verification of sub-surface storage in the geo-sphere. More recently, his focus is on bringing significant new and evolving technologies to an advanced level (but non-specialist) student, engineering and project management audience.
John has over 25 years experience in the IT and security sector. He is an often sought management consultant for large enterprise and is currently a member of the Federal Communication Commission's Homeland Security Network Reliabiltiy and Interoperability Council Focus Group on Cybersecurity, working in the Voice over Internet Protocol workgroup.
James F. Ransome, Ph.D., CISSP, CISM, has over 30 years experience in security operations and technology assessment as a corporate security executive and positions within the intelligence, DoD, and federal law enforcement communities. He has a Ph.D. in information systems specializing in information security and is a member of Upsilon Pi Epsilon (UPE), the International Honor Society for the Computing and Information Disciplines. He is currently Vice President of Integrated Information Security at CH2M HILL in Denver, CO.
George L. Stefanek, Ph.D., has over 18 years of experience as a systems administrator and manager of IS/IT departments. He has also consulted on information security issues for such clients as the U.S. Department of Defense.
Frank Thornton runs his own technology consulting firm, Blackthorn Systems, which specializes in information security and wireless networks. His specialties include wireless network architecture, design, and implementation, as well as network troubleshooting and optimization. An interest in amateur radio helped him bridge the gap between computers and wireless networks. Having learned at a young age which end of the soldering iron was hot, he has even been known to repair hardware on occasion.

In addition to his computer and wireless interests, Frank was a law enforcement officer for many years. As a detective and forensics expert he has investigated approximately one hundred homicides and thousands of other crime scenes. Combining both professional interests, he was a member of the workgroup that established ANSI Standard "ANSI/NIST-CSL 1-1993 Data Format for the Interchange of Fingerprint Information."

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