These functions work using » mcrypt. To use it, download libmcrypt-x.x.tar.gz from » http://mcrypt.sourceforge.net/ and follow the included installation instructions. Windows users will find all the needed compiled mcrypt binaries at » http://files.edin.dk/php/win32/mcrypt/.
As of PHP 5.0.0 you will need libmcrypt Version 2.5.6 or greater.
If you linked against libmcrypt 2.4.x or higher, the following additional block algorithms are supported: CAST, LOKI97, RIJNDAEL, SAFERPLUS, SERPENT and the following stream ciphers: ENIGMA (crypt), PANAMA, RC4 and WAKE. With libmcrypt 2.4.x or higher another cipher mode is also available; nOFB.