Cryptography Decrypted

Fundamental security concepts like cryptography and digital signatures are becoming as much a part of our everyday lives as megabytes and the Internet. Anyone working with computer security--security professionals, network administrators, IT managers, CEOs, and CIOs--need to have a comfortable understanding of the cryptographic concepts in this book.

Cryptography Decrypted shows you how to safeguard digital possessions. It is a clear, comprehensible, and practical guide to the essentials of computer cryptography, from Caesar's Cipher through modern-day public key. Cryptographic capabilities like detecting imposters and stopping eavesdropping are thoroughly illustrated with easy-to-understand analogies, visuals, and historical sidebars.

You need little or no background in cryptography to read Cryptography Decrypted. Nor does it require technical or mathematical expertise. But for those with some understanding of the subject, this book is comprehensive enough to solidify knowledge of computer cryptography and challenge those who wish to explore the high-level math appendix.

Divided into four parts, the book explains secret keys and secret key methods like DES, public and private keys, and public key methods like RSA; how keys are distributed through digital certificates; and three real-world systems. Numerous graphics illustrate and clarify common cryptographic terminology throughout.

• Secret key and secret key exchanges
• Public and private keys
• Digital signatures
• Digital certificates, Public Key Infrastructure (PKI), and PGP
• Hashes and message digests
• Secure e-mail, secure socket layer (SSL), and Internet Protocol Security (IPsec)
• Protecting keys
• Cryptographic attacks
• Authentication, confidentiality, integrity, and nonrepudiation

--From the Foreword by John Kinyon

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Praise For Cryptography Decrypted

"…For readers of all levels…. Explains key concepts of cryptography. Describes difficult concepts using visual guides and analogies…" -- Security Update, Windows 2000 Magazine, January 2001

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Preface

A Tool for Everyone

In the past, cryptography was used mainly to secure the communications of the powerful and influential, the military and royalty. But the widespread use of computers, and the attacks to which they are vulnerable, has expanded the need for secure communications around the globe. This book describes the protection afforded by modern computer cryptographic systems and explains how the pace of modern technology requires continuing attention to the security of those systems.

The advent of computers changed a great many things, but not the fundamentals of cryptography. Through stories and pictures, Cryptography Decrypted presents cryptography's evolution into a modern-day science, laying out patterns from the past that are applicable today. It also gives you a thorough understanding of terms that are destined to become as much a part of our language and life as megabyte and Internet. As you begin to think about controlling various aspects of your life using wired or wireless communication, on line all the time, your understanding of cryptography--its benefits and its pitfalls--will make you feel a little more in control of a rapidly changing world.

Because rapid advances in the speed of hardware will continue to threaten the security of current cryptographic methods, it's essential that you choose appropriate techniques and perform ongoing assessment if you want to maintain your digital security. You can make such choices and assessments only if you know the basic concepts of cryptography. Cryptography Decrypted offers you that knowledge through visual representation of difficult concepts, an easy-to-use reference for reviewing key cryptographic terminology, and instructive historical information.

You need little or no background in cryptography to read this book. Neither does it require technical or math genius. It's designed so that anyone from CIOs to self-taught computer enthusiasts--and everyone in between--can pick up this book without any knowledge of encryption and find it fascinating, understandable, and instructive.

If you have some understanding of computer cryptography, Cryptography Decrypted is systematic and comprehensive enough to solidify your knowledge. It provides a simple description of the component parts of secret key and public key cryptography. (Those who already understand and don't wish to cover any more material about secret key cryptography may choose to read only Parts II through IV, bypassing Part I.)

Throughout the book, we use images to clarify cryptographic terms. After explaining the basic cryptographic components, we describe real-world cryptographic systems, some possible attacks on those systems, and ways to protect your keys.

The book provides a historical framework on which to build your understanding of how and why computer cryptography works. After a discussion of how cryptography has evolved into an essential Internet tool, we analyze secret key exchange problems and then explain the evolution of public key cryptography, with its solution to the key exchange problem. Along the way we explain some simple background on the math tricks that make public key cryptography secure. Traditionally, those who have thoroughly understood cryptography have been trained as mathematicians or scientists. Our goal here is to explain computer cryptography with rather little discussion of math. If the esoteric details aren't of immediate concern to you, you can skip Chapter 11 ("Making Public Keys: Math Tricks"), Chapter 14 ("Message Digest Assurances"), and the appendixes without diminishing your understanding of the basic concepts. Appendix A describes some aspects of public key mathematics, including inverses, primes, the Fermat test, Diffie-Hellman, DSA, elliptic curve, and pseudo-random number generation. Appendix B provides details of IPsec, a security system introduced in Chapter 21.

Introduction

Welcome to the Front Line

If your computer is connected to or transmits over an electronic network, your data is on the front line. Attackers are getting more competent by the month, and their attacks more intrusive, virulent, and widespread--from Melissa to the Love Bug to the unknown virus that ate your hard drive.

Although few of us leave our valuables unlocked, few of us know how to use cryptographic locks to secure our digital possessions. By the time you finish reading this book, you will.

Most governments, including those of Canada, China, France, Saudi Arabia, and the United States, consider cryptographic tools to be munitions of war, so it's reasonable to think of potential attacks on your data as a kind of war. Your opponent is anyone who wants to read, modify, or destroy your private documents.

In large part, this is a book about the cryptographic keys and methods you use to safeguard your digital possessions. Figure I-1 shows cryptographic keys and the symbols we use to portray them. Part I of this book explains secret keys and secret key methods. Part II describes public and private keys and public key methods. Part III explains how keys are distributed, and Part IV shows how three real-world systems--secure mail, Secure Socket Layer (SSL), and Internet Protocol Security (IPsec)--use cryptographic keys and methods.

Need a Quick Read?

Table of Contents

Foreword.


Preface.


Introduction.

I. SECRET KEY CRYPTOGRAPHY.

II. PUBLIC KEY CRYPTOGRAPHY.

III. DISTRIBUTION OF PUBLIC KEYS.

IV. REAL-WORLD SYSTEMS.