Securing Windows NT/2000 Servers for the Internet

Cryptography Basics

You will find references to various types of encryption methods and algorithms throughout this book. This section is a very brief summary of some of the terms and algorithms relevant to discussions in later chapters. For more detailed information on this complex topic, consult a good cryptography reference.^[21]

Public Key Cryptography

With public key cryptography, each party has a key-pair consisting of a private key and a public key. The public key is published while the private key is kept secret. Data encrypted with the public keys can only be decrypted using the private key and vice versa. Public key cryptography can also be used for authentication (through the use of digital signatures).

An important advantage of public key cryptography is that there are less complicated key distribution problems. All parties that want to be able to communicate using public key cryptography need to publish their public key in some kind of directory. When Alice wants to send an encrypted message to Bob, she uses Bob’s public key to encrypt the data. Alice can also digitally sign a message by encrypting it with her private key. Bob can then decrypt the message using his private key and verify Alice’s signature by decrypting using her public key.

The main disadvantage is that public key cryptography is slow compared to symmetric key cryptography.

Two common public key systems are:

Rivest-Shamir-Adleman (RSA)

The RSA cryptosystem is the most widely used public key cryptosystem. ...