## Please post corrections as comments or an update. ##
A WARNING: MOST EMAILS, MOST INSTANT MESSANGER MESSAGES, AND MOST IRC TRAFFIC IS *NOT* ENCRYPTED. They are sent in plain text from your connection to the server, from where they are disseminated, again in plain text, to the recipient(s). DO NOT SHARE PERSONAL OR SENSITIVE INFORMATION OVER ANY OF THESE SERVICES, EVEN IF YOU TRUST THE PERSON YOU ARE TALKING TO.
PROXIES OR ENCRYPTED TUNNELS (EVEN SECURE SHELL) ARE NOT EXEMPT. Even if the connection between your computer and the server/proxy is encrypted, all communications from that server to anywhere else (email server, IM server, IRC server) are NOT.
## How to use GnuPG and FireGPG with Gmail. ##
Install FirePGP: http://getfiregpg.org/stable/firegpg.xpi and restart Firefox.
Install GnuPG (http://www.gnupg.org/download/index.en.html):
a. On a Mac: http://macgpg.sourceforge.net/, 1.4.9: http://prdownloads.sourceforge.net/macgpg/GnuPG1.4.9.dmg?download
b. On Linux: most distros should already have GnuPG installed. Type 'which gpg' at the command line and see what you get. Sources and binary packages for other systems can be found at the above gnupg.org address. Binaries compiled for specific distributions will probably be found in their package repository (if they have one).
c. On Windows: ftp://ftp.gnupg.org/gcrypt/binary/gnupg-w32cli-1.4.9.exe
d. On other systems: binaries are available for a large variety of Unix-based systems. When all else fails, source files can be found at the above gnupg.org address.
Generate your gpg key:
a. On Linux or a Mac: Bring up a terminal and type "gpg --gen-key".
b. On Windows: Bring up a Command Prompt (Start -> Run -> cmd.exe), navigate to the folder where you installed GnuPG, and type "gpg.exe --gen-key".
c. For other systems, consult the GnuPG documentation.
Notes:
Use a DSA key.
If you publish your key to a key server, it will be identified using your Name and Email address.
Once you have generated your key (which will take a while), open up Firefox and go Tools->FirePGP->Key Manager, and ensure that the key you created exists there.
When you now enter gmail and compose a new message, you should see "FirePGP" undearneath subject, followed by links for "Encrypt", "Sign", "Inline" and "Attachments". Clicking "Encrypt" will light up the Encrypt button, and pressing "Send" will ask you to select which key you wish to encrypt against.
For a test, you can encrypt a test email to yourself against your own key. It will send without asking you for a password. When you get the email back and click on it, you will see a short block of encoded text, and will then be queried for the passphrase for your key. Upon entering it, FirePGP will decrypt the email locally and display the result. It will also decrypt any other emails that come in encrypted against your public key automatically, unless you tell it not to store your passphrase, or you tell it to forget currently stored passphrases.
To share your public key with people, in Firefox, go to Tools -> FirePGP -> Export, and select your private key. It will then give you a large block of letters and numbers, encased with "OpenPGP" and a series of ----s. People will use this to encrypt their emails before sending them to you, and only you can decrypt them (using your private key).
To send encrypted emails, you need to know the person's public key. If you have this in a file, you can enter FirePGP's key manager and import it from there. If you have it on someone's web page, you can highlight the text of it, and use the "Import" option in the FirePGP menu. You will then be able to select this key to encrypt against as described above, and send them encrypted emails.
KNOWN ISSUE: Some Ubuntu systems have incorrect permissions for the ~/.gnupg folder. Use "sudo chown -R yourname:yourgrep ~/.gnupg" to rectify this issue.
## AGAIN: Don't share private or confidential information via unsecured channels. YOU COULD GET SOMEONE KILLED. ##
## Please post corrections as comments or an update. ##