Kerberos

Kerberos: An Authentication Service for Computer Networks - A technical paper documenting the system and standard. Includes diagrams and references.
http://gost.isi.edu/publications/kerberos-neuman-tso.html

Heimdal - An international free implementation. Includes downloads, distribution information and mailing list contacts.
http://www.pdc.kth.se/heimdal/

Cybersafe Ltd - Provides products for database security, web security, and security infrastructure based on the Kerberos protocol, and also provides Kerberos consulting and support.
http://www.cybersafe.ltd.uk

MIT Kerberos Consortium - Created to establish Kerberos as a universal authentication platform for the world's computer networks. Includes news and events, details of sponsors and those involved, and membership information.
http://www.kerberos.org/

Notes on Integrating Windows, RedHat, and HPUX Using Kerberos - Brief tutorial on configuring *nix systems to authenticate off a Microsoft Active Directory server.
http://barney.gonzaga.edu/~awithers/integration/

How to Kerberize your Site - Excellent tutorial on implementation. Contains detailed steps to follow for a successful installation, as well as answers to common questions.
http://www.ornl.gov/~jar/HowToKerb.html

GNU Shishi - Freely available implementation of Kerberos 5. Includes system documentation and downloads.
http://www.gnu.org/software/shishi/

Kerberos Network Authentication Service - A resource site with documentation, papers and software distributions. Software may be subject to US export control.
http://gost.isi.edu/info/kerberos/

Kerberos Reference Page - An index of related resources. Includes software distributions and patches, as well as user documentation.
http://www.contrib.andrew.cmu.edu/~shadow/kerberos.html

RFC 1510 - An overview and specification of the official internet protocol.
http://tools.ietf.org/html/rfc1510

Kerberos FAQ - Answers to frequently asked questions.
http://www.cmf.nrl.navy.mil/CCS/people/kenh/kerberos-faq.html

CERT Advisory: Buffer Overflow in Kerberos Administration Daemon - "Multiple Kerberos distributions contain a remotely exploitable buffer overflow in the Kerberos administration daemon. A remote attacker could exploit this vulnerability to gain root privileges on a vulnerable system." <small>(October 28, 2002)</small>
http://www.cert.org/advisories/CA-2002-29.html