North American Cryptography Archives - Strong cryptographic software, libraries, and information about cryptography, data security, and privacy.LBNL's Network Research Group - Tools such as tcpdump and traceroute.
SAINT - (Security Administrator's Integrated Network Tool) Scans systems and networks and reports potential vulnerabilities.
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.
GASP! -- Georgetown Automated Solaris Patchtool - Automate Sun's Patchdiag tool with a command-line or X-Windows interface.
mcrypt - mcrypt is a replacement for the unix crypt, using several block algorithms in several modes like cbc, cfb etc.
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.
Sudo - Set Userid without root password. History, downloads, documentation.
Pidentd - Daemon implementing IDENT protocol, it can be used to identify the user who initiated a TCP/IP connection
Virtual eXecuting Environment - VXE defines restrictions for filesystem and all syscalls. More convenient than chroot(); (free for non-commercial use).
LogSurfer - Allows improved monitoring and alerting based on the contents of system logs.
Logcheck - Automated scanning of unix logfiles for intrusion attempts and software failures. Search is via egrep patterns and results are emailed. Includes download, PGP signature, sample report and mailing list.
Netpassword - Changing passwords safely across the net.
