GNU Privacy Guard - OpenPGP (RFC2440) implementation from the GNU project. Encrypts/decrypts/signs/digests files using strong cryptography. FAQ, downloads, documentation. mcrypt - A replacement for the Unix crypt, using several block algorithms in several modes like cbc, and cfb. SAINT - (Security Administrator's Integrated Network Tool) Scans systems and networks and reports potential vulnerabilities. Postfix Mail Transfer Agent - Drop-in Sendmail replacement by Wietse Venema. Offers several features that make it difficult to crack. Tripwire Inc. - Offers IT security and regulatory compliance solutions through incident detection and continuous monitoring. 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. 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. 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. Pidentd - Daemon implementing IDENT protocol, it can be used to identify the user who initiated a TCP/IP connection 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. NMAP Network Scanner - Efficient stealth port scanner. Downloads, e-mail lists, news. 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! S4Software - Secure4Privilege is a tool for complete access control to commands and scripts without giving out the root password. LogSurfer - Allows improved monitoring and alerting based on the contents of system logs. 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. OpenSSH - Portable Distribution - Open source implementation of SSH1 and SSH2 protocols. Ported from OpenBSD by the OpenSSH portability team. Lynis - Unix system and security auditing tool.