PGP (short for Pretty Good Privacy) is a public key encryption program originally written by Phil Zimmermann in 1991. Over the past few years, PGP has got thousands of adherent supporters all over the globe
and has become a de-facto standard for encryption of email on the Internet.
If you don't know whether PGP is something for you, please take some time
to read Phil Zimmermann's article on
why you should use PGP and this document on how PGP works. Adam Back has written this history of PGP.
Contrary to what many people seem to think, PGP is perfectly legal to use, provided that you choose the right version and don't download the program from a site in the USA if you're somewhere else in the world.
Other PGP products
PGP is primarily used for encrypting email. PGPfone and PGPdisk are two other products that use PGP encryption technology to secure phone calls and encrypt disk partitions, respectively. The PGP message format has now been standardized through RFC 2440, and in the future we will undoubtedly see many new PGP compatible products.