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.
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I. SECRET KEY CRYPTOGRAPHY.1. Locks and Keys.
Locks and Combinations.
Defining Cryptographic Terms.
Making and Solving Puzzles.
Review.2. Substitution and Caesar's Cipher.
Cryptanalysis of Caesar's Cipher.
Empowering the Masses.
The Importance of Separating the Method and the Key.
A Weakness of Caesar's Ciphers: The Failure to Hide Linguistic Patterns.
More Complex Substitution: Vigenere's Cipher.
Review.3. Transposition Ciphers: Moving Around.
Patterns and Cryptanalysis.
Combining Substitution and Transposition.
Review.4. Diffuse and Confuse: How Cryptographers Win the End Game.
The Polybius Cipher.
The Principle of Confusion.
Cryptographic Locks and Keys.
Review.5. DES Isn't Strong Anymore.
The Historical Need for an Encryption Standard.
Cycling Through Computer Keys.
Double and Triple DES.
DES (and Other Block Cipher) Modes.
The Avalanche Effect.
Supplement: Binary Numbers and Computer Letters.
Review.6. Evolution of Cryptography: Going Global.
Commercial and Military Needs.
Entering the Computer Age.
Review.7. Secret Key Assurances.
An Authentication Attack.
Not Really Random Numbers.
Using the MAC for Message Integrity Assurance.
Why Bother Using a Message Authentication Code?
File and MAC Compression.
Nonrepudiation: Secret Keys Can't Do It.
Review.8. Problems with Secret Key Exchange.
The Problem and the Traditional Solution.
Using a Trusted Third Party.
Key Distribution Center and Key Recovery.
Problems with Using a Trusted Third Party.
Growth in the Number of Secret Keys.
Trust and Lifetime.
II. PUBLIC KEY CRYPTOGRAPHY.9. Pioneering Public Key: Public Exchange of Secret Keys.
The Search for an Innovative Key Delivery Solution.
Developing an Innovative Secret Key Delivery Solution.
First Attempt: A Database of Key/Serial Number Pairs.
Second Attempt: An Encrypted Database of Key/Serial Number Pairs.
Merkle's Insight: Individually Encrypted Key/Serial Number Pairs.
Black Hat's Frustrating Problem.
The Key to Public Key Technology.
A New Solution: Diffie-Hellman-Merkle Key Agreement.
Alice and Bob Openly Agree on a Secret Key.
Problems with the Diffie-Hellman Method.
Separate Encryption and Decryption Keys.
Review.10. Confidentiality Using Public Keys.
New Twists on Old Security Issues.
Distribution of Public Keys.
Review.11. Making Public Keys: Math Tricks.
Alice's Easy Problem.
Grade School Math Tricks.
More Grade School Math.
Division and Remainders: Modular Math.
Using Modular Inverses to Make a Public Key.
Putting It All Together.
Giving BlackHat a Difficult, Time-Consuming Problem.
Trapdoor to the Easy Problem.
Exercise: Find Which Numbers Sum to 103.
Review.12. Creating Digital Signatures Using the Private Key.
Written and Digital Signature Assurances.
Reviewing and Comparing Authentication.
Secret Key Authentication.
Private Key Authentication 117
Authentication and Integrity Using Private and Secret Keys.
Private Key Authentication Methods.
Assurances in Both Directions.
Summary of Public Key Assurances.
Public Key Means Public / Private Key.
Compressing before Signing.
Review.13. Hashes: Non-keyed Message Digests.
Detecting Unintentional Modifications.
Detecting Intentional Modifications.
Signing the Message Digest.
Detecting BlackHat's Forgery.
Supplement: Unsuccessfully Imitating a Message Digest.
Review.14. Message Digest Assurances.
Two Message Digest Flavors.
Non-keyed Message Digest Assurances.
Weak Collision Resistance.
Examples of One-way and Weak Collision Resistance.
Strong Collision Resistance.
Non-keyed Digest Implementations.
Keyed Message Digest Assurances.
A MAC Made with DES.
Message Digest Compression.
Digest Speed Comparisons.
Review.15. Comparing Secret Key, Public Key, and Message Digests.
Ease of Key Distribution.
Symmetric (Secret) Key.
Asymmetric (Public) Key.
III. DISTRIBUTION OF PUBLIC KEYS.16. Digital Certificates.
Verifying a Digital Certificate.
Attacking Digital Certificates.
Attacking the Creator of the Digital Certificate.
Malicious Certificate Creator.
Attacking the Digital Certificate User.
The Most Devastating Attack.
Understanding Digital Certificates: A Familiar Comparison.
Issuer and Subject.
Transfer of Trust from the Issuer to the Subject.
Issuer's Limited Liability.
More than One Certificate.
Fees for Use.
The Needs of Digital Certificate Users.
Getting Your First Public Key.
Certificates Included in Your Browser.
Review.17. X.509 Public Key Infrastructure.
Why Use X.509 Certificate Management?
What Is a Certificate Authority?
Application, Certification, and Issuance.
Polling and Pushing: Two CRL Delivery Models.
Building X.509 Trust Networks.
More Risks and Precautions.
Certification Practice Statement.
X.509 Certificate Data.
Challenge Response Protocol.
Review.18. Pretty Good Privacy and the Web of Trust.
The History of PGP.
Comparing X.509 and PGP Certificates.
Building Trust Networks.
Bob Validates Alice's Key.
Casey Validates Alice's Key Sent by Bob.
Dawn Validates Alice's Key Sent by Casey via Bob.
Web of Trust.
PGP Certificate Repositories and Revocation.
Compatibility of X.509 and PGP
IV. REAL-WORLD SYSTEMS.
E-mail Cryptographic Parameters.
Negotiation of SSL and IPsec Cryptographic Parameters.
User Initiation of Cryptographic E-mail, SSL, and Ipsec.19. Secure E-mail.
Generic Cryptographic E-mail Messages.
Invoking Cryptographic Services.
Confidentiality and Authentication.
Deterring E-mail Viruses.
Review.20. Secure Socket Layer and Transport.
History of SSL.
Overview of an SSL Session.
An SSL Session in Detail.
Hello and Negotiate Parameters.
Key Agreement (Exchange).
Confidentiality and Integrity.
Fixed and Ephemeral Diffie-Hellman.
Comparing TLS, SSL v3, and SSL v2.
A Big Problem with SSL v2.
A Possible Problem with TLS and SSL.
Generating Shared Secrets.
Bob Authenticates Himself to AliceDotComStocks.
Review.21. IPsec Overview.
IPsec Part 1: User Authentication and Key Exchange Using IKE.
SSL/TLS and IPsec Key Agreement.
Benefits of Two-Phase Key Exchange.
IPsec Part 2: Bulk Data Confidentiality and Integrity for Message or File Transport.
Protocol and Mode.
Implementation Incompatibilities and Complications.
Review.22. Cryptographic Gotchas.
Finding Your Keys in Memory.
Does Confidentiality Imply Integrity?
Example 2: Cut-and-Paste Attack.
Public Key as a Cryptanalysis Tool.
Example 1: The Chosen Plaintext Attack.
Public Key Cryptographic Standards.
Example 2: The Bleichenbacher Attack.
BlackHat Uses Bob's RSA Private Key.
Review.23. Protecting Your Keys.
Types of Smart Cards.
What's Inside a Smart Card.
Protections and Limitations.
Smart Card Attacks.
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.
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.
|A Devastating Opponent|
|In World War II the German Observation Service--Beobachtungs-Dienst, or B-Dienst--was a small group of codebreakers who played a powerful role in the Battle of the Atlantic. B-Dienst uncovered the positions of Allied convoys that German submarines then destroyed, devastating the Allied Atlantic forces from 1941 to 1943. For example, during three days in March 1943, the Germans sank 21 Allied vessels while losing only one submarine. Better communications security and new technologies such as sonar helped the Allies turn the tide.|
Need a Quick Read?
|Section||Chapter(s)||Major Points Covered|
|Part I: Secret Key||1-4||The difference between cryptographic methods and cryptographic keys. The security of modern cryptographic methods. Best feasible attack against a modern method: trying each key|
|5||Effect of technology in weakening DES|
|6||Historical insights into cryptography|
|7||Secret key assurances: confidentiality, authentication, and integrity|
|8||Maintenance and management problems in sharing secret keys|
|Part II: Public Key||9||Foundation of public key cryptography: easy and hard problems|
|10||Public key encryption and public key assurances|
|11||Simple cryptographic mathematics|
|12||Private key encryption and private key assurances|
|13||Detecting message modification with nonkeyed message digests and hashes|
|14||Message digest assurances|
|15||Comparing secret key, public key, and message digests|
|Part III: Distribution||16||Digital certificates: digitally signed public keys of Public Keys|
|17||x.509 digital certificates, certificate authorities, and certificate revocation|
|18||Pretty Good Privacy (PGP) compared to x.509|
|Part IV: Real-World||19-21||Examples of real-world systems (secure e-mail, SSL, IPsec) Systems|
|22||Some cryptographic attacks|
|23||Protecting your keys with smartcards|
|Appendixes||A||Mathematics underlying public key technology|