This part of the book provides a basic introduction to UNIX host security. These chapters are intended to be accessible to both users and system administrators.

• Chapter 3, Users and Passwords , is about UNIX user accounts. It discusses the purpose of passwords, explains what makes good and bad passwords, and describes how the crypt () password encryption system works.

• Chapter 4, Users, Groups, and the Superuser , describes how UNIX groups can be used to control access to files and devices. It also discusses the UNIX superuser and the role that special users play.

• Chapter 5, The UNIX Filesystem , discusses the security provisions of the UNIX filesystem and tells how to restrict access to files and directories to the file's owner, to a group of people, or to everybody on the computer system.

• Chapter 6, Cryptography , discusses the role of encryption and message digests in your security. It includes a discussion of how various popular encryption schemes, including the PGP mail package, work.