"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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I. WHAT EVERYONE SHOULD KNOW.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.
Summary.3. Why Is Wi-Fi Vulnerable to Attack?
Changing the Security Model.
What Are the Enemies Like?
Profit or Revenge Attackers.
Traditional Security Architecture.
Option 1: Put Wireless LAN in the Untrusted Zone.
Option 2: Make Wi-Fi LAN Trusted.
Danger of Passive Monitoring.
Summary.4. Different Types of Attack.
Classification of Attacks.
Attacks Without Keys.
Man-in-the-Middle Attack (Modification).
Attacks on the Keys.
Burying the Keys.
Attacking the Keys Through Brute Force.
II. THE DESIGN OF WI-FI SECURITY.5. IEEE 802.11 Protocol Primer.
Wireless LAN Organization.
Basics of Operation in Infrastructure Mode.
Connecting to an AP.
General Frame Formats.
Summary.6. How IEEE 802.11 WEP Works and Why It Doesn't.
Use of RC4 Algorithm.
Initialization Vector (IV).
Mechanics of WEP.
Integrity Check Value (ICV).
Preparing the Frame for Transmission.
RC4 Encryption Algorithm.
Why WEP Is Not Secure.
Message Modification Detection.
RC4 Weak Keys.
Direct Key Attacks.
Summary.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.
How the Layers Are Implemented.
Relationship of the Standards.
List of Standards.
Summary.8. Access Control: IEEE 802.1X, EAP, and RADIUS.
Importance of Access Control.
Authentication for Dial-in Users.
IEEE 802.1X in a Simple Switched Hub Environment.
IEEE 802.1X in Wi-Fi LANs.
EAP Message Formats.
EAPOL-Start. BHEADS = EAPOL-Key.
Messages Used in IEEE 802.1X.
RADIUS--Remote Access Dial-In User Service.
EAP over RADIUS.
Use of RADIUS in WPA and RSN.
Summary.9. Upper-Layer Authentication.
Who Decides Which Authentication Method to Use?
Use of Keys in Upper-Layer Authentication.
Certificates and Certification Authorities.
A Detailed Look at Upper-Level Authentication Methods.
Transport Layer Security (TLS).
Functions of TLS.
Relationship of TLS Handshake and WPA/RSN.
TLS over EAP.
Summary of TLS.
Obtaining the Ticket-Granting Ticket.
How Tickets Work.
Use of Kerberos in RSN.
Cisco Light EAP (LEAP).
Protected EAP Protocol (PEAP).
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.
Summary.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.
Summary of Key Hierarchies.
Details of Key Derivation for WPA.
Group Key Handshake.
Computing the Temporal Keys.
What Is TKIP and Why Was It Created?
IV Selection and Use.
Per-Packet Key Mixing.
TKIP Implementation Details.
Computation of the MIC.
Per-Packet Key Mixing.
Substitution Table or S-Box.
Phase 1 Computation.
Phase 2 Computation.
Modes of Operation.
Offset Codebook Mode (OCB).
How CCMP Is Used in RSN.
Steps in Encrypting a Transmission.
Overview of Implementation.
Steps in Encrypting an MPDU.
Summary.13. Wi-Fi LAN Coordination: ESS and IBSS.
ESS Versus IBSS.
Joining an ESS Network.
WPA/RSN Information Element.
Validating the Information Elements.
Preauthentication Using IEEE 802.1X.
IBSS Ad-Hoc Networks.
III. WI-FI SECURITY IN THE REAL WORLD.14. Public Wireless Hotspots.
Development of Hotspots.
Public Wireless Access Defined.
Barriers to Growth.
Security Issues in Public Hotspots.
How Hotspots Are Organized.
Different Types of Hotspots.
How to Protect Yourself When Using a Hotspot.
Personal Firewall Software.
Virtual Private Network (VPN).
Summary.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.
Problems Created by Man-in-the-Middle Attacks.
802.1x and EAP.
Layer 2 Denial-of-Service Attacks Against All Wi-Fi-Based Standards.
WPA Cryptographic Denial-of-Service Attack.
Summary.16. Actual Attack Tools.
Other Tools of Interest.
Summary.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.
Building an Open Source Access Point.
Making It All Work.
References and More Information.
APPENDIXES.Appendix A. Overview of the AES Block Cipher.
Finite Field Arithmetic.
Galois Field GF().
Steps in the AES Encryption Process.
Computing the Rounds.
Summary of AES.Appendix B. Example Message Modification.
Checking the MD5 Digest.
Checking the GPG Signature.Acronyms.
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, the reality is that most Wi-Fi wireless LANs operating in 2003, do so with no effective security at all. 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 through 2002 are completely inadequate - some would say completely broken. The reality is that 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 which just 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 re-configuration 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.
For many years Wi-Fi or IEEE802.11 wireless LANs were considered an interesting technology but not mainstream. This has all changed. It is no longer confined to technology addicts or experimenters in IT departments; it provides practical benefits, to ordinary people and everyday companies. There are really two categories of user: 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 might 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 to 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.
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 IEEE802.11 standard (IEEE802.11i) which 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 IEEE802.11i?"
"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 will answer. 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 types of questions for yourself.
In this book we look at security issues, protocols and application. An overview is provided for all the important protocols from IEEE802.11 and IEEE802.1X through to authentication protocols such as RADIUS and EAP. We cover the security protocols of WPA and IEEE802.11i 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. This book arms you with an understanding of Wi-Fi security so that you will know what you are doing - and why. It does not flood you with pages of installation and configuration instructions for specific vendor equipment, as that information changes and becomes obsolete frequently. 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 which did not hold true over time. We feel that administrators will not want to take at face value statements like "the new WPA and IEEE802.11i 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 re-established 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 IEEE802.11i 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 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 which 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 readers 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 IEEE802.11 for those who are not familiar with the protocol used to communicate over the air.
This book is organized into three sections. Roughly speaking these sections describe:
In the first section, "Wireless LAN Security Principals," we look at the issues that everybody should know about security. Some of these issues are common sense but many are things that you may not have thought about. If you are already security expert, and just looking to find out how security works for Wi-Fi, you might skim this section as many of the principals will be familiar.
The second section, "How Wi-Fi Security Works," starts with a primer on IEEE802.11 which 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. An understanding of the messages being sent between the Wi-Fi components is important to appreciate the security risks.
After the primer, the book delves into the various 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 IEEE802.11i 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 taken one layer at a time each part can be separately understood. Section two is divided into chapters, each dedicated to one piece of the solution. Section 2 ends with a technical review of the known attacks against existing wireless LANs and how these have been effective in the past. Reviewing these attacks after understanding the new security methods enables us to appreciate why the new methods are able withstand all known attacks to date.
The third section "Security in the Real World," comes back to practical issues. We start off with a review of security in "Hot spots" or public access networks. Such network access is becoming increasing popular in Internet cafes and airports; hot spots bring their own special security risks. We review the actual tools available on the Web which anyone can download for attacking wireless LANs. Our philosophy here is that it is only by sitting in the cockpit of enemy's plane that you can understand the threat it poses. Finally we 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 vendors will package the new security approaches in their 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 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 any short cuts that the vendors can provide us in simplifying or setting up the systems. However, remember that sales people 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 where you have choice and to tweak under the hood when you think necessary. Make better purchasing decisions and sleep well at night. Be informed.
That is the purpose of this book.
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