The tcb package contains core components of our "tcb" suite implementing the alternative password shadowing scheme on Openwall GNU/*/Linux (Owl). It is being made available separately from Owl primarily for use by other distributions. For more information, please refer to: http://www.openwall.com/tcb/ You need to have the password hashing framework introduced with crypt_blowfish patched into glibc to compile and use this. crypt_blowfish is available at: http://www.openwall.com/crypt/