PHP Manual

Runtime Configuration

The behaviour of these functions is affected by settings in php.ini.

**Mcrypt configuration options**
Name	Default	Changeable	Changelog
mcrypt.algorithms_dir	`NULL`	PHP_INI_ALL
mcrypt.modes_dir	`NULL`	PHP_INI_ALL

For further details and definitions of the PHP_INI_* modes, see the Where a configuration setting may be set.

Here's a short explanation of the configuration directives.

mcrypt.algorithms_dir string: The directory that contains the algorithms. Defaults to the directories compiled within libmcrypt, which is typically /usr/local/lib/libmcrypt. See mcrypt_list_algorithms() for additional details.
mcrypt.modes_dir string: The directory that contains the modes. Defaults to the directories compiled within libmcrypt, which is typically /usr/local/lib/libmcrypt. See mcrypt_list_modes() for additional details.