Methods of Signing with GPG

Using GPG

Step 1: Install software

We use the Homebrew package manager for this step.

brew install gpg2 gnupg pinentry-mac       

Step 2: Update ~/.gnupg/gpg-agent.conf

If this file does not exist, create it.

# Insert the following text
pinentry-program /usr/local/bin/pinentry-mac

Step 3: Update or Create ~/.gnupg/gpg.conf

If this file does not exist, create it.

# Uncomment within config (or add this line)
# This tells gpg to use the gpg-agent
use-agent

Step 4: Modify your Shell

Append the following to your ~/.bash_profile or ~/.bashrc or ~/.zshrc

...
export GPG_TTY=`tty`

Step 5: Restart your Terminal or source your ~/.*rc file

# on the built-in bash on macos use
source ~/.bash_profile
# if using bash through homebrew over ssh use
source ~/.bashrc
# and if using zsh
source ~/.zshrc

Step 6: Create your GPG Key

Run the following command to generate your key, note we have to use the --expert flag so as to generate a 4096-bit key.

gpg --full-gen-key

Step 7: Update the Permissions on your ~/.gnupg Directory

You will need to modify the permissions to 700 to secure this directory.

chmod 700 ~/.gnupg

Step 8: Answer the Questions

Once you have entered your options, pinentry will prompt you for a password for the new PGP key.

Please select what kind of key you want:
   (1) RSA and RSA (default)
   (2) DSA and Elgamal
   (3) DSA (sign only)
   (4) RSA (sign only)
Your selection? 4
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048) 4096
Requested keysize is 4096 bits
Please specify how long the key should be valid.
         0 = key does not expire
      <n>  = key expires in n days
      <n>w = key expires in n weeks
      <n>m = key expires in n months
      <n>y = key expires in n years
Key is valid for? (0) 3y
Key does not expire at all
Is this correct? (y/N) y

You need a user ID to identify your key; the software constructs the user ID
from the Real Name, Comment and Email Address in this form:
    "RandallTux (rndtx) <[email protected]>"

Real name: RandallTux
Email address: [email protected]
Comment:
You selected this USER-ID:
    "RandallTux <[email protected]>"

Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? o
You need a Passphrase to protect your secret key.

Step 9: Get your key info for Git, etc.

# List your keys
gpg -k

Step 10: Get your key id

Use the next command to generate a short form of the key fingerprint.

Copy the text after the rsa4096/ and before the date generated and use the copied id in step 13:

gpg -K --keyid-format SHORT
sec rsa4096/######## YYYY-MM-DD [SC] [expires: YYYY-MM-DD]

You need to copy the output similar to the example above where the ######## is.

Step 11: Export the fingerprint

In the output from step 10, the line below the row that says ‘pub’ shows a fingerprint-this is what you use in the placeholder. The output from below is what you copy to Github:

# The export command below gives you the key you add to GitHub
gpg --armor --export <your key id>

Step 12: Configure Git to use gpg

git config --global gpg.program $(which gpg)

Step 13: Configure Git to use your signing key

The below command needs the fingerprint from step 10 above:

git config --global user.signingkey 1111111

Step 14: Configure Git to sign all commits (Optional-you can configure this per repository too)

This tells Git to sign all commits using the key you specified in step 13.

git config --global commit.gpgsign true

Step 15: Perform a Commit

git commit -S -s -m "My Signed Commit"

Step 16: Pinentry Prompt

You will now be prompted by Pinentry for the password for your signing key. You can enter it into the Dialog box-with the option of saving the password to the macOS X Keychain.

Step 17: Submit your PGP key to Github to verify your Commits

Login into Github.com and go to your settings, SSH and GPG Keys, and add your GPG key from the page.

Step 18: Submitting Your Key to a Public Keyserver (very optional)

Before you jump on submitting your key to a service such as the MIT PGP Key Server, you should consider the following:

Troubleshooting

If you have any errors when generating a key regarding gpg-agent, try the following command to see what error it generates:

gpg-agent --daemon