To learn more about general issues of public key cryptography, the following pages should prove usefull: Netscaps's DevEdge online documentation provides an introduction to public key cryptography. This site covers the basics of internet security issues, encryption/decryption, signatures and certificates. Wikipedia, the online encyclopedia, provides a basic definition of public key cryptography, and includes many links to related topics, as well as some history of the beginnings of public key cryptography. GNU Privacy Guard (GnuPG, or GPG) is a free, open source alternative to PGP. The website provides documentation and guides on GnuPG in many different languages and formats. The English html version is available here. For the more technical user, there are several sites that provide more indepth, and advanced information on the features and usage of PGP. The Experimental Reference Center for Cryptographic Data Protection provides a wealth of information on using PGP. VolumeI: Essential Topics is more fundamental, explaining the core concepts of using PGP, while VolumeII: Special Topics covers more the advanced features of PGP. The Official PGP Users Guide, is a book written by the PGP's creator, Philip Zimmermann himself. "In addition to technical details, the User's Guide contains valuable insights into the social engineering behind the software engineering and into the legal, ethical, and political issues that have surrounded PGP since its initial release." The book is available through Amazon.com Project EVA - 2004