TrinityOS is a step-by-step, example-driven HOWTO on building a very functional Linux box with strong security in mind. TrinityOS is well known for its strong packet firewall ruleset, Chrooted and Split DNS (v9 and v8), secured Sendmail (8.x), Linux PPTP, Serial consoles and Reverse TELNET, DHCPd, SSHd, UPSes, system performance tuning, the automated TrinityOS-Security implementation scripts, and much more.
The Mandos system allows computers to have encrypted root file systems and at the same time be capable of remote or unattended reboots. The computers run a small client program in the initial RAM disk environment which will communicate with a server over a network. All network communication is encrypted using TLS. The clients are identified by the server using an OpenPGP key that is unique to each client. The server sends the clients an encrypted password. The encrypted password is decrypted by the clients using the same OpenPGP key, and the password is then used to unlock the root file system.
The cryptoswap package supports creating an encrypted swap partition when a system boots. This may be necessary on systems that use encrypted filesystems because plaintext secrets may be written to disk when memory is swapped to disk. The project also includes the ability to build a Linux initrd that supports booting with an encrypted root filesystem.