If you're using a GPG key that matches your committer identity and your verified email address associated with your account on GitHub.com, then you can begin signing commits and signing tags.

If you have multiple GPG keys, you need to tell Git which one to use.

1. Open TerminalTerminalGit Bash.

2. Use the gpg --list-secret-keys --keyid-format=long command to list the long form of the GPG keys for which you have both a public and private key. A private key is required for signing commits or tags.

   $ gpg --list-secret-keys --keyid-format=long

   Note: Some GPG installations on Linux may require you to use gpg2 --list-keys --keyid-format LONG to view a list of your existing keys instead. In this case you will also need to configure Git to use gpg2 by running git config --global gpg.program gpg2.

3. From the list of GPG keys, copy the long form of the GPG key ID you'd like to use. In this example, the GPG key ID is 3AA5C34371567BD2:

   $ gpg --list-secret-keys --keyid-format=long
   /Users/hubot/.gnupg/secring.gpg
   ------------------------------------
   sec 4096R/3AA5C34371567BD2 2016-03-10 [expires: 2017-03-10]
   uid Hubot 
   ssb 4096R/42B317FD4BA89E7A 2016-03-10

4. To set your GPG signing key in Git, paste the text below, substituting in the GPG key ID you'd like to use. In this example, the GPG key ID is 3AA5C34371567BD2:

   $ git config --global user.signingkey 3AA5C34371567BD2

5. If you aren't using the GPG suite, run the following command in the zsh shell to add the GPG key to your .zshrc file, if it exists, or your .zprofile file:

   $ if [ -r ~/.zshrc ]; then echo 'export GPG_TTY=$(tty)' >> ~/.zshrc; \
     else echo 'export GPG_TTY=$(tty)' >> ~/.zprofile; fi

   Alternatively, if you use the bash shell, run this command:

   $ if [ -r ~/.bash_profile ]; then echo 'export GPG_TTY=$(tty)' >> ~/.bash_profile; \
     else echo 'export GPG_TTY=$(tty)' >> ~/.profile; fi

6. Optionally, to prompt you to enter a PIN or passphrase when required, install pinentry-mac. For example, using Homebrew:

   $ brew install pinentry-mac
   $ echo "pinentry-program $(which pinentry-mac)" >> ~/.gnupg/gpg-agent.conf
   $ killall gpg-agent

Telling Git about your X.509 key

You can use smimesign to sign commits and tags using S/MIME instead of GPG.

1. Install smimesign.
2. Open TerminalTerminalGit Bash.
3. Configure Git to use S/MIME to sign commits and tags. In Git 2.19 or later, use the git config gpg.x509.program and git config gpg.format commands:

• To use S/MIME to sign for all repositories:

  $ git config --global gpg.x509.program smimesign
  $ git config --global gpg.format x509

• To use S/MIME to sign for a single repository:

  $ cd /path/to/my/repository
  $ git config --local gpg.x509.program smimesign
  $ git config --local gpg.format x509

  In Git 2.18 or earlier, use the git config gpg.program command:
• To use S/MIME to sign for all repositories:

  $ git config --global gpg.program smimesign

• To use S/MIME to sign for a single repository:

  $ cd /path/to/my/repository
  $ git config --local gpg.program smimesign

  If you're using an X.509 key that matches your committer identity, you can begin signing commits and tags.

1. If you're not using an X.509 key that matches your committer identity, list X.509 keys for which you have both a certificate and private key using the smimesign --list-keys command.

   $ smimesign --list-keys

2. From the list of X.509 keys, copy the certificate ID of the X.509 key you'd like to use. In this example, the certificate ID is 0ff455a2708394633e4bb2f88002e3cd80cbd76f:

   $ smimesign --list-keys
                ID: 0ff455a2708394633e4bb2f88002e3cd80cbd76f
               S/N: a2dfa7e8c9c4d1616f1009c988bb70f
         Algorithm: SHA256-RSA
          Validity: 2017-11-22 00:00:00 +0000 UTC - 2020-11-22 12:00:00 +0000 UTC
            Issuer: CN=DigiCert SHA2 Assured ID CA,OU=www.digicert.com,O=DigiCert Inc,C=US
           Subject: CN=Octocat,O=GitHub\, Inc.,L=San Francisco,ST=California,C=US
            Emails: octocat@github.com

3. To set your X.509 signing key in Git, paste the text below, substituting in the certificate ID you copied earlier.

• To use your X.509 key to sign for all repositories:

  $ git config --global user.signingkey 0ff455a2708394633e4bb2f88002e3cd80cbd76f

• To use your X.509 key to sign for a single repository:

  $ cd /path/to/my/repository
  $ git config --local user.signingkey 0ff455a2708394633e4bb2f88002e3cd80cbd76f