Introduction

Tech Decrypted

Taking the mystery out of learning cryptography

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.

	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.

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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
	B	IPsec details