Soon I'll make an 'Encryption' wiki page, but in the meantime, here are the basics of pgp's encryption setup, John. The whole system relies on a tweaked interpretation of the encryption philosophy called 'public-key encryption'. Let's say two users, Alice and Bob, want to exchange a message that is secret (email, in this case). Now, Alice has Thunderbird with PGP enabled, and according to the layout of her email message to Bob (the characters typed, etc.), a novel secret key is created, and, when the email is sent, that secret key, along with Alice's public key, is sent along with it. That way, when Bob receives the ciphertext (the encrypted plaintext of the email document), he can decipher it with the secret key that pgp sends along the way (granted he also has an email client with pgp somehow integrated).
For instance, take an email correspondence between Isaac and myself. We both have each other's public keys, and we can send encrypted emails to one another. Whenever I send an email to Isaac, Thunderbird prompts me for my "pass phrase" that corresponds with my email keys; that allows me to digitally "sign" the email. Whenever I receive an email from Isaac, I also type that same pass phrase, so that nobody but I can read the deciphered text; once I enter that pass phrase, Isaac's email is decrypted from cipher text back into plain text. This allows our conversations to be secure. To offer some context on what kind of security, take my Blackberry's email client. Though on my Thunderbird pgp-enabled browser on my computer can read Isaac's email perfectly fine, the email on my Blackberry is a bunch of random gibberish -- what is normally called 'cipher text'. This makes sure that only I can read this email after I've entered my secret pass phrase.
Hope that helped. Here's a tutorial on how to set up Thunderbird with pgp on a Windows machine: Install Thunderbird with pgp with Windows
--Gordonbr 03:33, 9 January 2011 (CST)