This is an archive of past FreeBSD releases; it's part of the FreeBSD Documentation Archive.
Cheswick, William R. and Steven M. Bellovin. Firewalls and Internet Security: Repelling the Wily Hacker. Reading, Mass. : Addison-Wesley, 1995. ISBN 0-201-63357-4
Garfinkel, Simson and Gene Spafford. Practical UNIX & Internet Security. 2nd Ed. O'Reilly & Associates, Inc., 1996. ISBN 1-56592-148-8
Garfinkel, Simson. PGP Pretty Good Privacy O'Reilly & Associates, Inc., 1995. ISBN 1-56592-098-8