PGP, which stands for Pretty Good Privacy, is a program that uses two different keys to encrypt (put into code) and decrypt (make readable) a message. The two different keys are mathematically linked together; but since there are literally trillions of different possibilities, no one else can read your message.
The two keys are named your Secret (or Private) Key, and your Public Key. Your Secret Key is kept by you; and only you should ever know the password (or passphrase) to access it. Your Public Key should be distributed as far as possible around the world. Then when you want to send me a message that you only want me to read, you can encrypt it with my Public Key. Since it is mathematically linked to my Secret Key, only I can then read the message.
But then how do I know that the message is really from you? You can’t get an ink pen out and put your signature across the envelope flap to prove to me that it is your letter. What you can do is use your Secret Key to encrypt the message as well. So what I would end up getting is a message that has been encrypted twice. I use your Public Key to make sure that the message is really from you; and I use my Secret Key to actually read the message.
If someone else intercepts the message, all they’ll be able to do is to prove that you sent the message to me. The actual text will be secure.
I know this sounds like a lot of hassle, but that’s the really cool thing about Pretty Good Privacy. PGP takes care of all of that hassle for you!
PGP 2.62 Documentation
The DOS version of PGP 2.62 comes with full documentation. The primary documents are PGPDOC1.TXT and PGPDOC2.TXT. I printed them out and started to play with PGP and found that it was a hassle to deal with the page numbering. So here are the same text files in Adobe Acrobat PDF files. They are a bit larger than the original text versions of the documentation, but are infinitely easier to use, either on screen or printed out.