Encryption/Decryption using GnuPG

June 12th, 2007 | security, technology, tip

So you have decided to make the jump to using encryption to protect sensitive information on the hard disk and while sending across the Internet. Great!. One of the best freeware programs available is GnuPG.

To get started, install gpg4win. Download, double-click on the downloaded file and you are good to go. After installation, when you right-click on a file, you should see a new option, GPGee, in your menu. This means everything went well with the install.

Now to go Start -> Programs -> GnuPG For Windows -> GPA

GPA (Gnu Privacy Assistant) is the heart of this program. What we will do next is generate keys for you to use. You see, this type of encryption depends on “keys” that have your unique signature. The only personal identification in the keys are your name and email address. I would suggest putting in your real name and a real email address you use. This is so others can find your keys easily. These keys are meant to be made public.

If you already have your own keys, skip forward to the “key import” section.

0. Generate Keys

When you started GPG, the program probably came up asking if you want to generate keys.

Say “Generate Keys” at this screen. You will be asked for your name and email address and a password and the program will generate a key for you in a few seconds. This key will show up in your “keyring”. A keyring is where you store your own key and other user’s keys. Your key is protected by the password you entered, so don’t forget the password. The initial keyring will just have the key you just generated.

1. Encrypting/Decrypting Files

To encrypt a file, right-click on the file and select “GPGee -> Sign and Encrypt”.

A window will pop up that will list all the keys that can be used to encrypt. First choose the encryption key (box at top) by checking the box. Next, select the signing key.

After you click “ok”, you will see a file with a *.gpg extension in the same folder. This is the encrypted version of the file.

To decrypt a file, we need to reverse this process. First, right-click on the encrypted file and choose “GPGee -> Verify/Decrypt”. This will ask for your password to unlock your key that will be used for decryption. You should get a success message box after decryption. The decrypted file will show up in the same folder.

2. Sending encrypted emails

Unfortunately,there is no easy way to use GnuPG to send encrypted emails.

Update: You can use thunderbird with Enigmail to automate this process.

Here’s what you can do.

Write your email in notepad or another text editor. Save the file.
Encrypt this file to get a file with *.gpg extension
Open the *.gpg file in notepad or another text editor
Use Ctrl+A to select the data in the file, Ctrl+C to copy the data
Paste this into your email client (Outlook, Hotmail, GMail whatever you use)

To decrypt any encrypted emails that you get:

Copy full email from your email client
Paste this into notepad or another text editor
Save the file with a *.gpg extension
Decrypt the file using the discussion in section 1.
The decrypted file will show up in the same folder

3. Sharing your key with others

This method of encryption works only when you have the keys of the people you want to send encrypted files/emails to. Others who need to send you encrypted files or emails need to know your keys also.