MacOS comes bundled with OpenSSH without the ability to create resident keys on a yubikey. In order for yubikey to be loaded via the ssh-agent, we require nix to be installed on the base system
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Assuming nix
is installed, you can run
user@system> nix-shell -p yubikey-manager openssh
to start an interactive nix shell with yubikey-manager
and openssh
readily available. We need ssh-agent
to be loaded.
user@system-nix>eval $(ssh-agent -s)
We are going to create two types of keys
- A signing key with
ed25519
- An auth key with
ecdsa
ssh-keygen
will create token handles for the key stored inside the yubikey. Those handles can safely be deleted.
ssh-keygen -O resident -O application=ssh:github-felsweg-sign-02 -C "github-felsweg-sign-02" -t ed25519-sk -q -N '' -f /Users/thm/.ssh/id_github_felsweg_sign_02
ssh-keygen -O resident -O application=ssh:github-felsweg-auth-02 -C "github-felsweg-auth-02" -t ecdsa-sk -q -N '' -f /Users/thm/.ssh/id_github_felsweg_auth_02
Both keys are created inside the yubikey as resident
keys, and can be loaded via
user@system-nix> ssh-add -K
ssh-add
will prompt you for the PIN for the yubikey (see yubikey-manager
manual on how to properly set the PIN).
If both keys are loaded successfully, you can list the keys and display the public key via
user@system-nix> ssh-add -L
This output something similar to this list:
sk-ecdsa-sha2-nistp256@openssh.com <public key>
sk-ssh-ed25519@openssh.com <public key>
After placing both keys successfully in GitHub at your profile, we can now test the connection to GitHub via
user@system-nix> ssh -T git@github.com
A short message should indicate the success of the connection
Hi <username>! You've successfully authenticated, but GitHub does not provide shell access.
Git can use the previously generated SSH key to sign messages.
git config --global user.name "User Name"
git config --global user.email "user.name@email.com"
git config --global commit.gpgsign true
git config --global gpg.format ssh
git config --global user.signingKey "key::sk-ssh-ecdsa <PUBLIC_KEY>"
Where <PUBLIC_KEY>
is the public part of your loaded signing key (again, list via ssh-add -L
to view your public keys )
If you used the --global
flag your ~/.gitconfig
should look like this
[user]
name = User Name
email = user.name@email.com
signingKey = key::sk-ssh-ed25519@openssh.com <PUBLIC_KEY>
[commit]
gpgsign = true
[gpg]
format = ssh
[gpg "ssh"]
allowedSignersFile = /Users/thm/.ssh/allowed_signers
Create a file called ~/.ssh/allowed_signers
with the following contents
user.name@email.com sk-ssh-ed25519@openssh.com <PUBLIC_KEY>
Create an empty project, run git init
in it to create a git repo and run
user@system-nix> git commit --allow-empty -m "this empty commit should be signed"
Then after committed successfully, you can verify the signature.
user@system-nix> git log --show-signature