Admin Tools-Software

The Coroner's Toolkit (TCT)
The Coroner's Toolkit (TCT) provides post-break-in data collection that could be useful in determining what happened. Less polished that the authors (Dan Farmer and Wietse Venema) usual work, the toolkit offers a patch-work of tools that help exhume interesting stuff from violated systems. Should be installed and examined before a break-in happens!
http://www.porcupine.org/forensics/tct.html

GNU Privacy Guard
OpenPGP (RFC2440) implementation from the GNU project. Encrypts/decrypts/signs/digests files using strong cryptography. FAQ, downloads, documentation.
http://www.gnupg.org/

LBNL's Network Research Group
Tools such as tcpdump and traceroute.
http://www-nrg.ee.lbl.gov/nrg.html

lsof
lsof is a tool for examining I/O channels open on your Unix system. These can include files, FIFOs and network sockets. This information can be extremely useful for security and a variety of other purposes. Works on most Unix-like systems.
http://freshmeat.net/projects/lsof

mcrypt
A replacement for the unix crypt, using several block algorithms in several modes like cbc, and cfb.
http://hq.hellug.gr/~mcrypt

NMAP Network Scanner
Efficient stealth port scanner. Downloads, e-mail lists, news.
http://www.nmap.org/

North American Cryptography Archives
Strong cryptographic software, libraries, and information about cryptography, data security, and privacy.
http://cryptography.org

OpenSSH - Portable Distribution
Open source implementation of SSH1 and SSH2 protocols. Ported from OpenBSD by the OpenSSH portability team.
http://www.openssh.org/portable.html

OpenSSL
The OpenSSL Project is a collaborative effort to develop a robust, commercial-grade, fully featured, and Open Source toolkit implementing the Secure Sockets Layer and Transport Layer Security protocols with full-strength cryptography world-wide.
http://www.openssl.org/

Pidentd
Daemon implementing IDENT protocol, it can be used to identify the user who initiated a TCP/IP connection
ftp://ftp.lysator.liu.se/pub/ident/servers/

Postfix Mail Transfer Agent
Drop-in Sendmail replacement by Wietse Venema. Offers several features that make it difficult to crack.
http://www.postfix.org

SAINT
(Security Administrator's Integrated Network Tool) Scans systems and networks and reports potential vulnerabilities.
http://www.wwdsi.com/saint/

Sudo
Run selected commands as root, with the users' own password. Allows the administrator to grant limited root privileges to a subset of users, without giving out the root password.
http://www.sudo.ws/

sudoscript
A pair of Perl scripts that provide an audited root shell using sudo and script(1). Tarballs, RPM's and individual components.
http://www.egbok.com/sudoscript

The SUS Home Page
SUS is a utility to allow a user (typically a system administrator) to run a single command as the super user.
http://pdg.uow.edu.au/sus/

Symark Software
Execute root-level commands and shell scripts without having to actually login as root. Control which users can log in and under which circumstances.
http://www.symark.com/products.htm

Tripwire Inc.
Commercial version of the original Unix file integrity scanner. Calculates and stores signatures of file permissions, ownership and contents. Scans the same files later, detecting changes.
http://www.tripwire.com/

Tripwire Open Source
Open source version of the original Unix file integrity scanner. Calculates and stores signatures of file permissions, ownership and contents. Scans the same files later, detecting changes. This open source version is targeted at Linux systems.
http://www.tripwire.org