mcrypt library

MCrypt is a replacement for the old crypt() package and crypt(1) command, with extensions. It allows developers to use a wide range of encryption functions, without making drastic changes to their code. It allows users to encrypt files or data streams without having to be cryptographers. Above all, it allows you to have some really neat code on your machine. :)

The companion to MCrypt is Libmcrypt, which contains the actual encryption functions themselves, and provides a standardized mechanism for accessing them.