Linux Security HOWTO
- General overview of security issues that face the administrator of Linux systems. It covers general security philosophy and a number of specific examples of how to better secure your Linux system from intruders.
- http://scrye.com/~kevin/lsh/t1.html

Firewall Piercing mini-HOWTO
- Tutorial on using ppp over telnet to do network stuff transparently through an Internet firewall. (François-René Rideau)
- http://en.tldp.org/HOWTO/Firewall-Piercing/

Linux Bridge+Firewall Mini-HOWTO
- A tutorial on how to setup a bridge and a firewall with Linux, by Peter Breuer.
- http://en.tldp.org/HOWTO/Bridge+Firewall.html

Linux IPCHAINS-HOWTO
- Describes how to obtain, install and configure the enhanced IP firewalling chains software for Linux, and how they might be used, by Paul Russell.
- http://en.tldp.org/HOWTO/IPCHAINS-HOWTO.html

Secure POP via SSH mini-HOWTO
- Explains how to set up secure POP connections using ssh, by Manish Singh.
- http://en.tldp.org/HOWTO/Secure-POP+SSH.html

Firewalling and Proxy Server HOWTO
- Teaches the basics of firewall systems and give you some detail on setting up both a filtering and proxy firewall on a Linux based PC, by Mark Grennan.
- http://en.tldp.org/HOWTO/Firewall-HOWTO.html

UnOfficial SELinux FAQ
- A technical FAQ for the NSA SELinux project, which covers installation and implementation issues.
- http://www.crypt.gen.nz/selinux/faq.html

Network Security Information: UNIX
- Network Security Library has links to many UNIX (and, especially, Linux) security articles on host hardening, security admin guides, and special purpose hardening tips.
- http://secinf.net/unix_security/

Linux Security White Papers
- A small collection of Linux security white papers and other information resources. The papers cover secure shell (ssh), host security, and firewalls.
- http://www.ists.dartmouth.edu/IRIA/knowledge_base/

Setting up a secure Linux server
- Setting up a secure Linux server using RedHat and the Linux From Scratch system.
- http://www.fiveanddime.net/ss/secureserver.html

Securing NIS
- Provides a checklist on how to secure UNIX/Linux NIS (formerly YP) services in an intranet environment.
- http://www.eng.auburn.edu/users/doug/nis.html

Rusty's Remarkably Unreliable Guides
- Netfilter project provides HOWTOs for packet filtering, NAT and netfilter code hacking for Linux.
- http://www.samba.org/netfilter/unreliable-guides/

Ritter's Crypto Glossary and Dictionary of Technical Cryptography
- Hyperlinked definitions and discussions of many cryptographic, mathematics, logic, statistics, and electronics terms used in cipher construction and analysis.
- http://www.ciphersbyritter.com/GLOSSARY.HTM

Installing a firewall, Part 1
- Get the details of a secure Trustix 1.1 installation
- http://www.itworld.com/Sec/2211/LWD111010fwinstall1/

Linuxs security basics
- How to achieve the goal of every system admin: boring, predictable computers
- http://www.itworld.com/Man/3872/lw-01-security/

YoLinux: Internet Server Security HowTo and Tutorial
- This tutorial covers the installation and use of hacker protection software such as Portsentry, tripwire, ssh. It also covers configuration and administration steps to make a Linux server secure against hackers.
- http://yolinux.com/TUTORIALS/LinuxTutorialInternetSecurity.html

A Simple Scheme to Make Passwords Based on One-Way Functions Much Harder to Crack
- Discusses the possibility that crackers might generate and distribute a massive list of encrypted passwords.
- ftp://ftp.cs.arizona.edu/reports/1994/TR94-34.ps

Introduction to Linux Networking and Security
- Brief introduction to the IP networking services, how to configure them, and how to set up a relatively secure Linux workstation. Published in ACM Crossroads, the ACM student magazine.
- http://www.acm.org/crossroads/xrds6-1/linuxsec.html

Linux Firewall Howto
- Firewall HOWTO collection, ids, nids, hardening, penetration testing, auditing
- http://www.linux-sec.net/

A Short History of Cryptography
- A brief historical analysis of the management of cryptography.
- http://www.all.net/books/ip/Chap2-1.html

Linux Administrator's Security Guide
- A comprehensive security guide aimed at administrators and users, available online in Acrobat PDF format, by Kurt Seifried.
- https://www.seifried.org/lasg/