The Zend Developer Zone has a new tutorial posted today showing how to use the open source encryption tool GnuPG from inside PHP.
While GnuPG works very well as a standalone tool, it also plays very well with PHP. This integration is possible due to PHP's ext/gnupg extension, which provides a flexible and powerful API to access GnuPG functions for encryption, decryption, message signing and verification, and key maintenance. And your mission (should you choose to accept it) will be to accompany me over the next few pages, while I give you a crash course in this API, showing you how easy it is to integrate these functions into your next PHP application.
The tutorial walks you through some of the basic concepts behind the "lock and key" GnuPG implements and how to get the extension installed so you can follow along. His examples range from a basic encryption of a string out to a full encrypt/decrypt example, how to sign information with a key and even a method for sending an encrypted message.