Special Edition Using Linux®, Sixth Edition

Encryption and Pretty Good Privacy (PGP)

Picture sending out a private letter to someone through the U.S. Postal Service, written on a postcard. Everyone who comes across that post card can see it, right? Therefore, it does not require a major stretch of the imagination to understand why private letters are typically sent to their destinations sealed in envelopes. If the letter is delivered incorrectly, or if some other problem with delivery develops, the letter is sent back still sealed in the envelope. At no point was the privacy of that letter compromised (unless someone decided to rip the letter open and read it).

Now, picture email over the Internet, or even within a small network. At least one machine other than the sending machine receives ...