It’s personal. It’s private. And it’s no one’s business but yours. You may be planning a political campaign, discussing your taxes, or having an illicit affair. Or you may be doing something that you feel shouldn’t be illegal, but is. Whatever it is, you don’t want your private electronic mail (E-mail) or confidential documents read by anyone else.

Philip Zimmermann, Why Do You Need PGP?.

For as long as people have needed to conduct private conversations across distances, a variety of encryption methods have been used to protect secret communications. However, the introduction of electronic communications networks raised an old encryption problem to a new level — how do two people establish secure communications when they live so far apart that they can’t meet first to exchange a secret decryption key?

The solution to this problem is an encryption method called Public Key Cryptography (PKC), an ingenious mathematical structure that doesn’t need participants to meet beforehand to conduct secure communications. PKC technology also provides a clever method of attaching an encrypted signature to a message to guarantee authenticity. PKC is now the engine for almost all high grade encryption on the Internet, including financial transactions on websites and implementation of the highest level virtual private networks. The following sections provide more information.