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-O application=ssh:KEY_NAME names the key, so you can identify it more easily later, very handy if you generate a few.
-C "YOUR_EMAIL" comment the key with your email.
Adding the new keys
Now that you have generated a key which you can use, you will need to add it to your current ssh-agent session. You can do that by first starting the agent like so:
SSH_KEY="id_ed25519"
ssh-add ~/.ssh/$SSH_KEY
Authenticating with GitHub
In order to authenticate with GitHub you will have to add your new public key to your GitHub profile over at -> github.com/settings/keys. You can copy the public key to clipboard by running
pbcopy <~/.ssh/$SSH_KEY.pub
Testing authentication
Now that we've added our ssh key to GitHub we can test that the setup works correctly by running:
ssh -T git@github.com
If this worked correctly you should be greeted by a "welcoming message".
NOTE: In order to make sure that you are using the new SSH key consider moving out existing keys from the ~/.ssh directory just for this test.
Start by checking that there aren't any previous ssh keys inside the FIDO2 authenticator of your YubiKey. You can check if they exist by running the command below:
ykman fido credentials list
If the command above outputs a string mentioning "ssh" or "openssh", then you have already got a key generated and store on your YubiKey.
-t ed25519-sk is the key type, two options are possible ecdsa-sk and ed25519-sk (sk stands for security key). If you do not know which one to choose, stick with ed25519-sk.
-O application=ssh:KEY_NAME names the key, so you can identify it more easily later, very handy if you generate a few.
-O no-touch-required prevents you from having to touch the YubiKey every time you want to use the key.
-O resident tells OpenSSH to store the key on the YubiKey.
-C "YOUR_EMAIL" comment the key with your email.
Adding the new keys
Now that you have generated a key which you can use, you will need to add it to your current ssh-agent session. You can do that by first starting the agent like so:
Add the key on the YubiKey temporarily to our current session with the command below:
ssh-add -K
If you would like to have it permanently available on the system you can run the command:
This retrieves our ssh key from our YubiKey and puts the private (still protected by YubiKey) and public key in the current working directory, then rename them accordingly to id_ed25519_sk and id_ed25519_sk.pub, then place them in your ~/.ssh directory so ssh can detect them.
Authenticating with GitHub
In order to authenticate with GitHub you will have to add your new public key to your GitHub profile over at -> github.com/settings/keys. You can copy the public key to clipboard by running
pbcopy <~/.ssh/$SSH_KEY.pub
Testing authentication
Now that we've added our ssh key to GitHub we can test that the setup works correctly by running:
ssh -T git@github.com
If this worked correctly you should be greeted by a "welcoming message".
NOTE: In order to make sure that you are using the new SSH key consider moving out existing keys from the ~/.ssh directory just for this test.
To sign Git commits, you need a gpg key. GPG stands for GNU Privacy Guard and is the de facto implementation of the OpenPGP message format. PGP stands for ‘Pretty Good Privacy’ and is a standard to sign and encrypt messages.
Setting up
Install with Homebrew:
$ brew install gpg pinentry-mac
Create config files for gpg and the gpg-agent. The agent will make sure you don’t have to type in your GPG passphrase for every commit.
Note: if you’re on Intel, /opt/homebrew should be /usr/local.
Add the following lines to ~/.zshrc (the GPG_TTY environment variable is a requirement for GPG; the second line launches the gpg-agent when you open a new shell):
export GPG_TTY=$(tty)
gpgconf --launch gpg-agent
To effectuate the changes to .zshrc, type:
$ source~/.zshrc
Create GPG keypair
Now that your environment is properly set up, we need to generate a public/private GPG keypair.
$ gpg --full-gen-key
A wizard is printed to your terminal. You should configure as follows:
Kind of key: 4 (RSA, sign only)
Keysize: 4096
Expiration: 2y (your key will expire after 2 years; you should set a reminder somewhere)
Real name: <your github username>
Email address: <your email address>
Note: I heartily recommend setting your email address to your 'noreply' GitHub address: username@users.noreply.github.com. You can find your email address on the GitHub Email settings page. Note that if you created a GitHub account after July 2017, your address will also have an ID prefixed to your username; read more here.
The final step in setting up the GPG keypair is typing a passphrase. Make sure it is strong and you have it safely stored in your password vault (I recommend Bitwarden). Whoever has your passphrase can sign your commits and there is no way to prove it wasn’t you.
After creating the keypair, output similar to the following is printed to your terminal:
The string of characters is your key ID. To confirm you can sign messages with your newly created key, enter in your terminal:
$ echo'it works'| gpg --clearsign
A message similar to this should appear:
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256
it works
-----BEGIN PGP SIGNATURE-----
<many characters>
-----END PGP SIGNATURE-----
Adding to Git
We need to add your key to your git config, and to GitHub. First, you need to find the key ID. The (short) ID uses the last 8 characters of the key that was printed to the terminal before. You can retrieve it:
The 56667778 bit after rsa4096/ is your short key ID. We need it to configure Git to sign commits and tags. Replace the user.signingkey value below with your own key ID:
Git needs to know your email, and it needs to be the same as the one for your GPG key. This email address needs to be verified on GitHub as well. If you use your ‘private’ GitHub email, that’s already the case.
Finally, you need to add your public GPG key to GitHub. Again, make sure to replace the ID with your own ID:
$ gpg --armor --export 56667778
Outputs:
-----BEGIN PGP PUBLIC KEY BLOCK-----
<many characters>
-----END PGP PUBLIC KEY BLOCK-----
You need to copy the whole block and add it to GitHub. If you’re not sure what to copy, use this command:
$ gpg --armor --export 56667778 | pbcopy
The | pbcopy part will pipe the output of the first part directly to your copy-paste memory.
Go to the GitHub SSH and GPG keys section, click [New GPG key] and paste into the box. Click [Add GPG key], and you’re done!
After getting this done, and after having made your first signed commit, you can see the ‘Verified’ badge on GitHub for that commit (see an example here). Your GPG key ID will be shown when the badge is clicked.
Visual Studio Code
If you use Visual Studio Code, you can turn on signing by changing a setting.
Open VSCode, go to Preferences > Settings, and search for git.enableCommitSigning. Turn this setting on, and you’re good to go.
On older MacOS versions or certain (remote) shells, you might encounter the error inappropriate ioctl for device. (This error might also turn up if you haven’t configured the GPG_TTY environment variable correctly, see above for instructions.) More context here. You can fix this by using the so called ‘loopback’ option to enter your passphrase directly on the CLI.
Edit gpg.conf and add:
pinentry-mode loopback
Edit gpg-agent.conf and add:
allow-loopback-pinentry
Now, when the agent wants your passphrase it will simply render a basic password input on the CLI:
$ echo'it works'| gpg --clearsign
Enter passphrase:
3. Using SourceTree
If you use SourceTree, you should point it to the right binary. A solution is posted on Stack Overflow, make sure to also follow this comment.
4. X.509 Certificate
If the commit still can’t be signed, it could be that you use an X.509 certificate to sign your commits (this might be the case in a corporate environment, for example). Tell Git about it:
$ git config --global gpg.x509.program gpg
If that doesn’t cut it, install smimesign, an S/MIME signing utility for use with Git with Homebrew:
$ brew install smimesign
Then, configure git to use an X.509 certificate and smimesign as the gpg program.
The .zshrc file is a configuration file for your zsh shell (rc stands for runcom) that might not exist yet on your system. You can easily create it like this:
$ cd~
$ touch .zshrc
These kinds of 'dot files' are usually not edited with standard MacOS apps like TextEdit. You can use vi or nano from the command line instead. Find some useful instructions here.