Real 802.11 Security: Wi-Fi Protected Access and 802.11i

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" Real 802.11 Security provides clear descriptions of current and emerging security techniques. The authors handle complex topics nicely, and offer significant clarification of IEEE draft standards."
--Russ Housley, IETF Security Area Director and founder of Vigil Security, LLC

"This is certainly the definitive text on the internals of 802.11 security!"
--John Viega, founder and chief scientist, Secure Software, Inc.

"This book keeps the exposition as straightforward as possible and enables you to cut through the maze of acronyms, hacking tools, rumored weaknesses, and vague vendor security claims to make educated security decisions when purchasing or deploying WLAN."
--Simon Blake-Wilson, Director of Information Security, BCI

Business professionals and advanced home users are captivated by the convenience of working on wireless networks. But how can privacy and security be maintained effectively? Real 802.11 Security describes an entirely new approach to wireless LAN security based on the latest developments in Wi-Fi technology. This is the book that will show you how to establish real security within your Wi-Fi LAN.

Recent developments in Wi-Fi security achieve what no amount of reconfiguration can do: They solve the problem at the source. Wi-Fi Protected Access (WPA) repairs weaknesses in existing Wi-Fi systems and is designed to allow software upgrades. The upcoming 802.11i standard will offer a much higher level of security than previously offered and will provide flexible, extremely secure solutions for future products.

Real 802.11 Security addresses the theory, implementations, and reality of Wi-Fi security. It provides an overview of security issues, explains how security works in Wi-Fi networks, and explores various security and authentication protocols. The book concludes with an in-depth discussion of real-world security issues and attack tools.

Written by two experts in wireless security, Jon Edney and William Arbaugh, this book shows you how to stay informed and aware when making security decisions, and what steps you can take to implement the most effective, proactive wireless security now and in the future.


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Product Details

  • ISBN-13: 9780321136206
  • Publisher: Addison-Wesley
  • Publication date: 8/8/2003
  • Pages: 451
  • Product dimensions: 6.92 (w) x 9.05 (h) x 1.02 (d)

Meet the Author

Jon Edney specializes in wireless networking and is a key contributor to the development of IEEE 802.11 systems. As a member of the technology consultancy Symbionics Networks, he deployed the first low-cost 802.11 designs. In 1996, Edney cofounded InTalk, Inc., the first IEEE 802.11 company to develop WLAN access points. After InTalk was acquired by Nokia Corporation, he focused on the application of Wi-Fi to public access networks. He is an active member of the IEEE 802.11 TGi security group.

William A. Arbaugh is an assistant professor of computer science at the University of Maryland in College Park, where he conducts research in information systems security. Arbaugh served as a senior computer scientist for the National Security Agency's Office of Research and Technology, and then as senior technical advisor for the Office of Advanced Network Programs. He has many publications to his credit and has delivered papers at security-related conferences such as IEEE, SANS, USENIX, and Comdex.


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Table of Contents




1. Introduction.

Setting the Scene.

Roadmap to the Book.

Notes on the Book.

2. Security Principles.

What Is Security?

Good Security Thinking.

1. Don't Talk to Anyone You Don't Know.

2. Accept Nothing Without a Guarantee.

3. Treat Everyone as an Enemy until Proved Otherwise.

4. Don't Trust Your Friends for Long.

5. Use Well-Tried Solutions.

6. Watch the Ground You Are Standing on for Cracks.

Security Terms.


3. Why Is Wi-Fi Vulnerable to Attack?

Changing the Security Model.

What Are the Enemies Like?

Gaming Attackers.

Profit or Revenge Attackers.

Ego Attackers.

Traditional Security Architecture.

Option 1: Put Wireless LAN in the Untrusted Zone.

Option 2: Make Wi-Fi LAN Trusted.

Danger of Passive Monitoring.


4. Different Types of Attack.

Classification of Attacks.

Attacks Without Keys.


Man-in-the-Middle Attack (Modification).

Attacks on the Keys.

One-Time Passwords.

Burying the Keys.

Wireless Attacks.

Attacking the Keys Through Brute Force.

Dictionary Attacks.

Algorithmic Attacks.



5. IEEE 802.11 Protocol Primer.


Wireless LAN Organization.

Basics of Operation in Infrastructure Mode.



Connecting to an AP.


Sending Data.

Protocol Details.

General Frame Formats.

AC header.

Management Frames.

Radio Bits.


6. How IEEE 802.11 WEP Works and Why It Doesn't.




Use of RC4 Algorithm.

Initialization Vector (IV).

WEP Keys.

Mechanics of WEP.


Integrity Check Value (ICV).

Preparing the Frame for Transmission.

RC4 Encryption Algorithm.

Why WEP Is Not Secure.


Access Control.

Replay Prevention.

Message Modification Detection.

Message Privacy.

RC4 Weak Keys.

Direct Key Attacks.


7. WPA, RSN, and IEEE 802.11i.

Relationship Between Wi-Fi and IEEE 802.11.

What Is IEEE 802.11i?

What Is WPA?

Differences Between RSN and WPA.

Security Context.


Security Layers.

How the Layers Are Implemented.

Relationship of the Standards.

List of Standards.

Pictorial Map.


8. Access Control: IEEE 802.1X, EAP, and RADIUS.

Importance of Access Control.

Authentication for Dial-in Users.

IEEE 802.1X.

IEEE 802.1X in a Simple Switched Hub Environment.

IEEE 802.1X in Wi-Fi LANs.

EAP Principles.

EAP Message Formats.





Messages Used in IEEE 802.1X.

Authentication Sequence.

Implementation Considerations.

RADIUS--Remote Access Dial-In User Service.

RADIUS Mechanics.


Use of RADIUS in WPA and RSN.


9. Upper-Layer Authentication.


Who Decides Which Authentication Method to Use?

Use of Keys in Upper-Layer Authentication.

Symmetric Keys.

Asymmetric Keys.

Certificates and Certification Authorities.

A Detailed Look at Upper-Level Authentication Methods.

Transport Layer Security (TLS).

Functions of TLS.

Handshake Exchange.

Relationship of TLS Handshake and WPA/RSN.

TLS over EAP.

Summary of TLS.

Kerberos V5V5.

Using Tickets.

Kerberos Tickets.

Obtaining the Ticket-Granting Ticket.

Service Tickets.

Cross-Domain Access.

How Tickets Work.

Use of Kerberos in RSN.

Cisco Light EAP (LEAP).

Protected EAP Protocol (PEAP).

Phase 1.

Phase 2.

Status of PEAP.

Authentication in the Cellular Phone World: EAP-SIM.

Overview of Authentication in a GSM Network.

Linking GSM Security to Wi-Fi LAN Security.


Status of GSM-SIM Authentication.


10. WPA and RSN Key Hierarchy.

Pairwise and Group Keys.

Pairwise Key Hierarchy.

Creating and Delivering the PMK.

Computing the Temporal Keys.

Exchanging and Verifying Key Information.

Completing the Handshake.

Group Key Hierarchy.

Summary of the Key Establishment Process.

Key Hierarchy Using AES-CCMP.

Mixed Environments.

Summary of Key Hierarchies.

Details of Key Derivation for WPA.

Four-Way Handshake.

Group Key Handshake.

Nonce Selection.

Computing the Temporal Keys.


11. TKIP.

What Is TKIP and Why Was It Created?

TKIP Overview.

Message Integrity.

IV Selection and Use.

Per-Packet Key Mixing.

TKIP Implementation Details.

Message Integrity--Michael.


Computation of the MIC.

Per-Packet Key Mixing.

Substitution Table or S-Box.

Phase 1 Computation.

Phase 2 Computation.




Why AES?

AES Overview.

Modes of Operation.

Offset Codebook Mode (OCB).

How CCMP Is Used in RSN.

Steps in Encrypting a Transmission.

CCMP Header.

Overview of Implementation.

Steps in Encrypting an MPDU.

Decrypting MPDUs.


13. Wi-Fi LAN Coordination: ESS and IBSS.

Network Coordination.

ESS Versus IBSS.

Joining an ESS Network.

WPA/RSN Information Element.

Validating the Information Elements.

Preauthentication Using IEEE 802.1X.

IBSS Ad-Hoc Networks.



14. Public Wireless Hotspots.

Development of Hotspots.

Public Wireless Access Defined.

Barriers to Growth.

Security Issues in Public Hotspots.

How Hotspots Are Organized.


Access Points.

Hotspot Controllers.

Authentication Server.

Different Types of Hotspots.



Coffee Shops.


How to Protect Yourself When Using a Hotspot.

Personal Firewall Software.

Virtual Private Network (VPN).


15. Known Attacks: Technical Review.

Review of Basic Security Mechanisms.



Review of Previous IEEE 802.11 Security Mechanisms.


RC4 and WEP.

Integrity and Authentication.

Attacks Against the Previous IEEE 802.11 Security Mechanisms.


Access Control.


Man-in-the-Middle Attacks.

Management Frames.

ARP Spoofing.

Problems Created by Man-in-the-Middle Attacks.

802.1x and EAP.


Denial-of-Service Attacks.

Layer 2 Denial-of-Service Attacks Against All Wi-Fi-Based Standards.

WPA Cryptographic Denial-of-Service Attack.


16. Actual Attack Tools.

Attacker Goals.



Example Scenarios.





Other Tools of Interest.




17. Open Source Implementation Example.

General Architecture Design Guidelines.

Protecting a Deployed Network.

Isolate and Canalize.

Upgrade Equipment's Firmware to WPA.

What to Do If You Can't Do Anything.

Planning to Deploy a WPA Network.

Deploying the Infrastructure.

Add a RADIUS Server for IEEE 802.1X Support.

Use a Public Key Infrastructure for Client Certificates.

Install Client IEEE 802.1X Supplicant Software.

Practical Example Based on Open Source Projects.

Server Infrastucture.

Building an Open Source Access Point.

Making It All Work.



References and More Information.


Appendix A. Overview of the AES Block Cipher.

Finite Field Arithmetic.





Galois Field GF().


Steps in the AES Encryption Process.

Round Keys.

Computing the Rounds.


Summary of AES.

Appendix B. Example Message Modification.

Appendix C. Verifying the Integrity of Downloaded Files.

Checking the MD5 Digest.

Checking the GPG Signature.




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Why This Book Now?

Ask anyone with a computer whether they want to be protected against strangers reading their data or planting viruses. Not really worth the effort, is it? Everyone wants this type of protection. However, most Wi-Fi wireless LANs operating in 2003 have no effective security. In fact, so many Wi-Fi LANs operate without security that an entire new hobby, "war driving," has sprung up in which folks drive around detecting and connecting to unsuspecting networks for fun. There are Web sites that publish the location and details of unprotected networks that are found--there are bound to be some near you! This problem is the result of people being unaware of the danger, but you are different, right?

The fact that you are reading this preface means that you are aware of the need to take active steps to implement security. Already, you may have implemented some security approach, perhaps as recommended by the supplier of the equipment you installed. Would that this were enough. The horrible truth is that the security systems shipped with Wi-Fi systems over the period from 1999 to 2002 are completely inadequate, some would say completely broken. Any computer-literate person can now download from the Internet tools that will attack and break into the first-generation Wi-Fi systems.

This book will show you how to tip the balance back in your favor--how to establish real security within your Wi-Fi LAN. It is not just about configuring your computer correctly or choosing good passwords, although these things are important. There are many books that focus on "parameter setting." What we describe in this book is a whole new approach to wireless LAN security enabled by the recent development of new core technology for Wi-Fi. The new developments achieve what no amount of reconfiguration can do: they solve the problem at the source. In this book we show how the new approaches work and how they should be applied to maximum effect. Whether you are a system administrator or an advanced home user, this book will open your eyes to current weaknesses and practical, implementable solutions.

To Wi-Fi or Not to Wi-Fi

For many years, Wi-Fi or IEEE 802.11 wireless LANs were considered an interesting technology but not mainstream. This has changed. Now ordinary people and companies, not just technology addicts and experimenters in IT departments, see the practical benefits of this technology. There are two categories of users: business and home. Corporations set up Wi-Fi LANs to allow rapid network deployment, to reduce the cost of installing wiring, and to give workers more flexibility in where and when they work. Home users also want to avoid installing wiring and like the ability to use a laptop on the couch or in a comfy chair outside.

System administrators have a big problem when it comes to Wi-Fi LANs. On the one hand they recognize the benefits of wireless both for their own configuration management and for users. On the other hand, they must not deploy anything that will be a serious security threat. We say "serious" because there is always some security risk in any technology deployment. The only truly secure network is no network. So system administrators have to choose between banning Wi-Fi networks or figuring out how to obtain the needed level of security. Experienced system administrators recognize that any new system component brings both benefits and risks. The problem with Wi-Fi up to now has been how to evaluate the risk.

The Cavalry Is Here

In 2001 those few who deployed security often relied on the original Wi-Fi security method, called WEP. Regrettably, and quite suddenly, it was discovered that WEP had major security flaws and, while arguably better than nothing, customers were left without effective protection. The result, in 2002, was an unparalleled effort on the part of the industry to devise a replacement for WEP, something that would be impregnable, but which could be used to upgrade the existing installed systems. In 2003 we see the results of this effort being deployed.

The new solutions for Wi-Fi security are being delivered in two installments. The first installment is called Wi-Fi Protected Access (WPA), announced by the Wi-Fi Alliance at the end of 2002. WPA has been specifically designed to allow software upgrade of most existing Wi-Fi systems. It repairs all the security weaknesses found in older Wi-Fi systems and has been developed to provide system administrators with a solution to the security dilemma.

In time WPA will be incorporated into a new version of the IEEE 802.11 standard (IEEE 802.11i) that is incomplete at the time of writing. This will provide a flexible and extremely secure solution for all future products. WPA offers levels of security much higher than previously available. The failure of WEP was a sharp wake-up call for the industry and the prevailing mood during 2002 was "we will never let this happen again." As a result, the best experts have participated in creating the new solution and the results have been reviewed worldwide prior to completion.

Naturally, change brings questions:

"Should I implement WPA now rather than wait for IEEE 802.11i?"
"What do I do with my existing WEP equipment/Can I upgrade it?"
"Is it now safe to put Wi-Fi inside the firewall?"

These are the types of questions that this book answers. We could answer them right here: "yes," "yes," "yes," but our goal in writing is to ensure that you understand enough about the mechanics to answer these questions for yourself.

In this book we look at security issues, protocols, and applications. An overview covers all the important protocols from IEEE 802.11 and IEEE 802.1X through to authentication protocols such as RADIUS and EAP. We cover the security protocols of WPA and IEEE 802.11i in detail. We also look at the real-world tools that have been used to attack Wi-Fi systems and you will learn why these will no longer be a threat.


This book is written principally for system administrators but will also be useful to technically oriented home users and design engineers. It focuses on why the new Wi-Fi security methods are secure and how they work. You will finish with an understanding of Wi-Fi security so you will know what you are doing, and why. The book does not flood you with pages of installation and configuration instructions for specific vendor equipment, as that information changes frequently and becomes obsolete. You should use this book alongside vendor documentation to create customized security solutions.

System administrators have been badly burned in the past by assurances that Wi-Fi LANs had effective built in security, assurances that did not hold true over time. We feel that administrators will not want to take at face value statements like "the new WPA and IEEE 802.11i methods are completely secure." They should be able to see for themselves how the security methods are implemented and understand for themselves why the types of weakness that existed previously have been overcome. Only when this trust is reestablished can administrators continue deployment in comfort. This book attempts to provide all the information needed for this understanding.

If you are a design engineer in any networking field, wireless or otherwise, you will find this book relevant. The security technologies incorporated into WPA and IEEE 802.11i are the state of the art for data networking, and it is much easier to learn and understand technology when it is described in the context of a real system. It seems likely that some of the techniques incorporated into the wireless LAN area will also be applied to wired LANs in the future.

If you are just generally interested in the area, you will find lots of material describing the approach to security that is needed to provide a robust defense. You may choose to skip some of the chapters that describe the protocol and you will probably be surprised to see the real examples of hacking tools presented in the later chapters.

We assume that you have a reasonable understanding of how computer networks operate. You don't need to be an expert, especially to understand the first part of the book, but we presume you know what a Wi-Fi access point does and how it is connected to the rest of the network. We don't explain terms like Ethernet or TCP/IP in detail. There is a primer on IEEE 802.11 if you are not familiar with the protocol used to communicate over the air.


This book is organized into three parts. Roughly speaking, these parts describe:

  • Things you should know about security in general
  • How both the old and new methods of security work in Wi-Fi networks
  • Real-world issues and examples of attack tools that have been (and continue to be) used

In Part I, "What Everyone Should Know," we review issues that everybody should know about security. Some of these issues are commonsense, but you may not have thought about them. If you are already a security expert and exploring how security works for Wi-Fi, consider skimming this material because many of the principles will be familiar.

Part II, "The Design of Wi-Fi Security," starts with a primer on IEEE 802.11 that runs through the basics of Wi-Fi systems communication. It describes the types of messages that are exchanged, usually hidden from the end user, and explains how a portable device like a laptop can find, select, and connect to an access point. The primer contains a moderate, but hopefully not oppressive, amount of detail. You need to understand the messages being sent between the Wi-Fi components to appreciate the security risks.

After the primer, the book delves into the security protocols for Wi-Fi. It describes the original Wi-Fi security approach, WEP, and explains why this method is no longer considered secure. It then covers the new approaches of Wi-Fi Protected Access (WPA) and IEEE 802.11i Robust Security Networks. Both the new methods share a common approach and are scalable from small networks of a few devices up to international corporations. The solution involves many pieces assembled in layers. This makes the approach appear complicated but, if you take one layer at a time, you can understand each part separately.

Part III, " Wi-Fi Security in the Real World," returns to practical issues. We start off with a review of security in hotspots or public access networks. Such network access is becoming increasingly popular in Internet cafes and airports; and hotspots bring their own special security risks. We then look at some of the tools available on the Web that anyone can download for attacking wireless LANs. Our philosophy here is that it is only by sitting in the cockpit of the enemy's plane that you can understand the threat it poses. Finally we make recommendations about practical actions for designing a secure network and look at an open source project that has been established to set up and test the security approaches that you will need to deploy.

We have not focused on specific vendor products. In the end each vendor will package the new security approaches in its own way. They will hide the complexity behind graphical user interfaces and try to simplify the installation and maintenance as much as possible. All this can make life easy for you if you are deploying the equipment. However, while the work required to install systems can be boiled down, we believe that the understanding of what is going on should be sharpened up. Why? Because at the end of the day, you're the one that gets hurt by attacks, not the vendor.

There is no "neighborhood watch" scheme for network security. The administrator or owner of the equipment must be aware of the risks and be proactive in response. Of course most people can't afford, and don't want, to spend all their time working on security issues. We all welcome shortcuts from vendors that simplify or set up the systems. However, remember that salespeople are optimists, but security people must be pessimists.

Our advice to you is simple: Be informed. Take advantage of vendor tools to simplify installation and management but understand what they are doing. Know enough to decide what is best for you and to tweak under the hood when you think it is necessary. Make better purchasing decisions and sleep well at night. Helping you meet these goals is the purpose of this book.


Readers should be aware that some of the standards described in this book are still under development and may have changed by the time this book is published. The information in this book is intended to be descriptive and should not be relied upon for implementation as a substitute for the published industry standards.


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