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Summary
Summary
Cryptography is at the heart of computer security: without it, secure e-commerce and Internet communications would be impossible. Decision-makers and sophisticated computer users need to understand cryptography -- but most explanations are highly mathematical and technical. Cryptography Decrypted explains cryptography in "plain English" -- and is authoritative and thorough enough to address the needs of professionals. It explains the processes step-by-step, with extensive visuals. The authors present the elements of cryptography systems; public key infrastructure (PKI); and the IPSec standard for virtual private network security; then review real-world systems and their applications. They show how real-world systems are attacked, and how to protect them; introduce essential cryptographic terms; and present the fascinating history of cryptography through sidebars highlighting its important events, people, and breakthroughs. For every decision-maker and computer user who needs to understand cryptography, this book is also ideal for security pros who need to educate management about cryptography.
Author Notes
H.X. Mel consults and develops computer systems for organizations such as Lucent, Xerox, MIT, the U.S. Government, Motorola, Goldman Sachs, and PricewaterhouseCoopers. Doris Baker is a freelance technical writer and editor.
0201616475AB04062001
Excerpts
Excerpts
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. 0201616475P04062001 Excerpted from Cryptography Decrypted by Pankaj Jalote, H. X. Mel, Doris M. Baker All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.Table of Contents
Foreword | p. xv |
Preface | p. xvii |
Introduction | p. xix |
Part I Secret Key Cryptography | p. 1 |
Chapter 1 Locks and Keys | p. 3 |
Locks and Combinations | p. 3 |
Defining Cryptographic Terms | p. 5 |
Making and Solving Puzzles | p. 6 |
Review | p. 6 |
Chapter 2 Substitution and Caesar's Cipher | p. 7 |
Cryptanalysis of Caesar's Cipher | p. 10 |
Empowering the Masses | p. 11 |
The Importance of Separating the Method and the Key | p. 12 |
Adding Keys | p. 13 |
A Weakness of Caesar's Ciphers: The Failure to Hide Linguistic Patterns | p. 14 |
More Complex Substitution: Vigenere's Cipher | p. 15 |
Review | p. 19 |
Chapter 3 Transposition Ciphers: Moving Around | p. 21 |
Patterns and Cryptanalysis | p. 22 |
Adding Complexity | p. 23 |
Computer Transposition | p. 25 |
Combining Substitution and Transposition | p. 26 |
Review | p. 28 |
Chapter 4 Diffuse and Confuse: How Cryptographers Win the End Game | p. 29 |
Diffusion | p. 29 |
The Polybius Cipher | p. 30 |
The Principle of Confusion | p. 33 |
Cryptographic Locks and Keys | p. 34 |
Review | p. 35 |
Chapter 5 DES Isn't Strong Anymore | p. 37 |
The Historical Need for an Encryption Standard | p. 37 |
Cycling Through Computer Keys | p. 40 |
Double and Triple DES | p. 41 |
DES (and Other Block Cipher) Modes | p. 42 |
The Avalanche Effect | p. 42 |
Supplement: Binary Numbers and Computer Letters | p. 43 |
Review | p. 44 |
Chapter 6 Evolution of Cryptography: Going Global | p. 45 |
Early Cryptography | p. 46 |
Commercial and Military Needs | p. 48 |
Entering the Computer Age | p. 49 |
Review | p. 51 |
Chapter 7 Secret Key Assurances | p. 53 |
Confidentiality | p. 54 |
Authentication | p. 55 |
An Authentication Attack | p. 57 |
Not Really Random Numbers | p. 57 |
Integrity | p. 59 |
Using the MAC for Message Integrity Assurance | p. 60 |
Why Bother Using a Message Authentication Code? | p. 62 |
File and MAC Compression | p. 62 |
Nonrepudiation: Secret Keys Can't Do It | p. 63 |
Review | p. 64 |
Chapter 8 Problems with Secret Key Exchange | p. 65 |
The Problem and the Traditional Solution | p. 66 |
Using a Trusted Third Party | p. 68 |
Key Distribution Center and Key Recovery | p. 70 |
Problems with Using a Trusted Third Party | p. 71 |
Growth in the Number of Secret Keys | p. 71 |
Trust and Lifetime | p. 72 |
Review | p. 72 |
Part II Public Key Cryptography | p. 75 |
Chapter 9 Pioneering Public Key: Public Exchange of Secret Keys | p. 77 |
The Search for an Innovative Key Delivery Solution | p. 77 |
Developing an Innovative Secret Key Delivery Solution | p. 77 |
First Attempt: A Database of Key/Serial Number Pairs | p. 78 |
Second Attempt: An Encrypted Database of Key/Serial Number Pairs | p. 79 |
Merkle's Insight: Individually Encrypted Key/Serial Number Pairs | p. 80 |
Black Hat's Frustrating Problem | p. 81 |
The Key to Public Key Technology | p. 82 |
A New Solution: Diffie-Hellman-Merkle Key Agreement | p. 84 |
Alice and Bob Openly Agree on a Secret Key | p. 84 |
Problems with the Diffie-Hellman Method | p. 86 |
Separate Encryption and Decryption Keys | p. 86 |
Review | p. 88 |
Chapter 10 Confidentiality Using Public Keys | p. 89 |
New Twists on Old Security Issues | p. 89 |
Confidentiality Assurances | p. 92 |
Distribution of Public Keys | p. 92 |
Two-Way Confidentiality | p. 94 |
Review | p. 95 |
Chapter 11 Making Public Keys: Math Tricks | p. 97 |
Alice's Easy Problem | p. 98 |
Grade School Math Tricks | p. 100 |
More Grade School Math | p. 101 |
Division and Remainders: Modular Math | p. 103 |
Modular Inverses | p. 106 |
Using Modular Inverses to Make a Public Key | p. 109 |
Putting It All Together | p. 110 |
Giving BlackHat a Difficult, Time-Consuming Problem | p. 110 |
Trapdoor to the Easy Problem | p. 111 |
Knapsack Cryptography | p. 112 |
Modulo Calculations | p. 112 |
Exercise: Find Which Numbers Sum to 103 | p. 112 |
Review | p. 113 |
Chapter 12 Creating Digital Signatures Using the Private Key | p. 115 |
Written and Digital Signature Assurances | p. 116 |
Reviewing and Comparing Authentication | p. 117 |
Secret Key Authentication | p. 117 |
Private Key Authentication | p. 117 |
Authentication and Integrity Using Private and Secret Keys | p. 119 |
Private Key Authentication Methods | p. 120 |
RSA | p. 120 |
DSA | p. 121 |
Signing Terminology | p. 122 |
Nonrepudiation | p. 122 |
Assurances in Both Directions | p. 123 |
Summary of Public Key Assurances | p. 123 |
Public Key Means Public / Private Key | p. 124 |
Assurance Initiated | p. 124 |
Compressing before Signing | p. 124 |
Review | p. 125 |
Chapter 13 Hashes: Non-keyed Message Digests | p. 127 |
Detecting Unintentional Modifications | p. 129 |
Detecting Intentional Modifications | p. 131 |
Signing the Message Digest | p. 133 |
Detecting BlackHat's Forgery | p. 135 |
Replay Attacks | p. 136 |
Supplement: Unsuccessfully Imitating a Message Digest | p. 137 |
Review | p. 138 |
Chapter 14 Message Digest Assurances | p. 141 |
Two Message Digest Flavors | p. 141 |
Non-keyed Message Digest Assurances | p. 143 |
One-wayness | p. 143 |
Collision Resistance | p. 143 |
Weak Collision Resistance | p. 144 |
Examples of One-way and Weak Collision Resistance | p. 145 |
Strong Collision Resistance | p. 147 |
Non-keyed Digest Implementations | p. 150 |
Keyed Message Digest Assurances | p. 151 |
A MAC Made with DES | p. 151 |
DES-MAC Security | p. 152 |
Message Digest Compression | p. 154 |
Digest Speed Comparisons | p. 155 |
Hashed MAC | p. 155 |
Review | p. 156 |
Chapter 15 Comparing Secret Key, Public Key, and Message Digests | p. 157 |
Encryption Speed | p. 157 |
Key Length | p. 158 |
Ease of Key Distribution | p. 158 |
Cryptographic Assurances | p. 159 |
Symmetric (Secret) Key | p. 159 |
Asymmetric (Public) Key | p. 159 |
Review | p. 161 |
Part III Distribution of Public Keys | p. 163 |
Chapter 16 Digital Certificates | p. 165 |
Verifying a Digital Certificate | p. 167 |
Attacking Digital Certificates | p. 167 |
Attacking the Creator of the Digital Certificate | p. 168 |
Malicious Certificate Creator | p. 168 |
Attacking the Digital Certificate User | p. 168 |
The Most Devastating Attack | p. 168 |
Understanding Digital Certificates: A Familiar Comparison | p. 169 |
Issuer and Subject | p. 169 |
Issuer Authentication | p. 169 |
Transfer of Trust from the Issuer to the Subject | p. 170 |
Issuer's Limited Liability | p. 171 |
Time Limits | p. 171 |
Revoking Trust | p. 171 |
More than One Certificate | p. 172 |
Fees for Use | p. 172 |
The Needs of Digital Certificate Users | p. 172 |
Getting Your First Public Key | p. 173 |
Certificates Included in Your Browser | p. 174 |
Review | p. 174 |
Chapter 17 X.509 Public Key Infrastructure | p. 177 |
Why Use X.509 Certificate Management? | p. 178 |
What Is a Certificate Authority? | p. 179 |
Application, Certification, and Issuance | p. 179 |
Certificate Revocation | p. 181 |
Polling and Pushing: Two CRL Delivery Models | p. 182 |
Building X.509 Trust Networks | p. 182 |
Root Certificates | p. 183 |
More Risks and Precautions | p. 187 |
Distinguished Names | p. 188 |
Certification Practice Statement | p. 189 |
X.509 Certificate Data | p. 189 |
Challenge Response Protocol | p. 190 |
Review | p. 190 |
Chapter 18 Pretty Good Privacy and the Web of Trust | p. 193 |
The History of PGP | p. 193 |
Comparing X.509 and PGP Certificates | p. 194 |
Building Trust Networks | p. 196 |
Bob Validates Alice's Key | p. 196 |
Casey Validates Alice's Key Sent by Bob | p. 197 |
Dawn Validates Alice's Key Sent by Casey via Bob | p. 198 |
Web of Trust | p. 200 |
PGP Certificate Repositories and Revocation | p. 200 |
Compatibility of X.509 and PGP | p. 201 |
Review | p. 201 |
Part IV Real-World Systems | p. 203 |
E-mail Cryptographic Parameters | p. 204 |
Negotiation of SSL and IPsec Cryptographic Parameters | p. 204 |
User Initiation of Cryptographic E-mail, SSL, and IPsec | p. 205 |
Chapter 19 Secure E-mail | p. 207 |
Generic Cryptographic E-mail Messages | p. 207 |
Invoking Cryptographic Services | p. 209 |
Confidentiality and Authentication | p. 211 |
Choosing Services | p. 211 |
Positioning Services | p. 212 |
Deterring E-mail Viruses | p. 213 |
Review | p. 213 |
Chapter 20 Secure Socket Layer and Transport Layer Security | p. 215 |
History of SSL | p. 216 |
Overview of an SSL Session | p. 216 |
An SSL Session in Detail | p. 218 |
Hello and Negotiate Parameters | p. 219 |
Key Agreement (Exchange) | p. 221 |
Authentication | p. 222 |
Confidentiality and Integrity | p. 223 |
TLS Variations | p. 224 |
Anonymous Diffie-Hellman | p. 224 |
Fixed and Ephemeral Diffie-Hellman | p. 225 |
Comparing TLS, SSL v3, and SSL v2 | p. 225 |
A Big Problem with SSL v2 | p. 225 |
A Possible Problem with TLS and SSL | p. 225 |
Generating Shared Secrets | p. 226 |
Bob Authenticates Himself to AliceDotComStocks | p. 227 |
Review | p. 227 |
Chapter 21 IPsec Overview | p. 229 |
Enhanced Security | p. 229 |
Key Management | p. 230 |
Manual Distribution | p. 231 |
Automated Distribution | p. 231 |
IPsec Part 1: User Authentication and Key Exchange Using IKE | p. 232 |
SSL/TLS and IPsec Key Agreement | p. 232 |
Security Association | p. 232 |
Phases | p. 233 |
IKE Nomenclature | p. 235 |
Benefits of Two-Phase Key Exchange | p. 235 |
IPsec Part 2: Bulk Data Confidentiality and Integrity for Message or File Transport | p. 237 |
Protocol and Mode | p. 238 |
ESP Examples | p. 241 |
AH Examples | p. 243 |
Management Control | p. 244 |
Implementation Incompatibilities and Complications | p. 245 |
Review | p. 246 |
Chapter 22 Cryptographic Gotchas | p. 247 |
Replay Attack | p. 247 |
Man-in-the-Middle Attack | p. 247 |
Finding Your Keys in Memory | p. 249 |
Does Confidentiality Imply Integrity? | p. 249 |
Example 1 p. 250 | |
Example 2 Cut-and-Paste Attack | p. 250 |
Public Key as a Cryptanalysis Tool | p. 251 |
Example 1 The Chosen Plaintext Attack | p. 251 |
Public Key Cryptographic Standards | p. 253 |
Example 2 The Bleichenbacher Attack | p. 253 |
BlackHat Uses Bob's RSA Private Key | p. 253 |
Review | p. 257 |
Chapter 23 Protecting Your Keys | p. 259 |
Smart Cards | p. 259 |
Types of Smart Cards | p. 260 |
What's Inside a Smart Card | p. 261 |
Protections and Limitations | p. 261 |
Smart Card Attacks | p. 261 |
Review | p. 262 |
Epilogue | p. 263 |
Appendix A Public Key Mathematics (and Some Words on Random Numbers) | p. 267 |
Appendix B (A Few) IPsec Details | p. 321 |
Bibliography | p. 337 |
Index | p. 345 |