"The Official PGP User's Guide", Philip Zimmermann
"PGP: Pretty Good Privacy", Garfinkel
"Protect Your Privacy", Stallings
"E-Mail Security", Bruce Schneier
"Computer Privacy Handbook", Andre Bacard
These and some related works are also in the security and encryption menu. In preparing this column, I was asked for a list of PGP related Web sites. If you do a search, you will find that everyone and his dog has a mention of PGP on their pages, without much information about PGP itself. Here are some pages that provide information, links, and access to the software itself.
If you want info on the *US* version, try Phil's Pretty Good Software or Pretty Good Privacy (PGP) Info Archive.
If you want the *international* version (arguably superior), try the International PGP FAQ
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