Sensitive information often is stored on database servers and other storage facilities for later retrieval. At this point, it is critical to have at your disposal a facility that allows you, as a developer, to secure that data at storage time and retrieve the information you are looking for when you need it.

PHP offers an extension that allows developers to use the Mcrypt Library (mcrypt.sf.net) to secure data by encrypting it and later decrypting it. The documentation of the Mcrypt extension for PHP is located at [url=http://www.php.net/mcrypt]www.php.net/mcrypt[/url], and it should be studied carefully before implementation.

The Mcrypt extension supports an impressive array of algorithms, including triple-DES, Blowfish, Twofish and Two-Way. Using the Mcrypt extension is not a very intuitive process if you are not familiar with encryption; it can become quite confusing because of the variety of block algorithms and encryption modes available.

Read the full article at Linux Journal with a sample of a typical use of Mcript Extension.