SECRET KEY CRYPTOGRAPHY

In 1977, two innovations in computer cryptography forever changed 3,500
years of message disguise engineering and brought cryptography closer to be-
ing a tool everyone would need and use. Part I, “Secret Key,” explains the con-
cepts used to develop one of these innovations—Data Encryption Standard
(DES)—and leads into the second innovation, public key cryptography, dis-
cussed in Part II.

Part I describes the current state of secret key computer cryptography. The
first five chapters explain two important concepts:
• Secret key cryptography offers secure ways to store secrets.
• The attacker’s most feasible attack against these secure methods is to
try each possible key.
To prove these two concepts, Chapters 1 through 5 quickly proceed from
ancient to modern cryptographic methods. If you’re familiar with these two
concepts, you may choose to skip to Chapter 6. That said, we believe the first
five chapters offer a quick and instructive overview that will help you understand
secret key cryptographic protective devices.
Chapter 6 shows how cryptography evolved into a mathematical science.
Chapter 7 describes protections and assurances available with secret key
cryptography.
Chapter 8 explains why secret key cryptography, by itself, is not sufficient
to protect communications on the Internet. The bulk of the book and appen-
dixes explain public key cryptography and demonstrate why the Internet
needs it.