Forward GnuPG agent from macOS to Linux

Run gpg once as your to create the directory structure

gpg --list-keys

Edit /etc/ssh/sshd_config to include the line:

StreamLocalBindUnlink yes

Add this line to your user's $HOME/.bashrc:

gpgconf --create-socketdir

Add this line to the file: $HOME/.gnupg/gpg-agent.conf

extra-socket $HOME/.gnupg/S.gpg-agent.extra

Reload your current gpg-agent:

gpg-connect-agent reloadagent /bye

Edit $HOME/.ssh/config to forward the gpg-agent socket. Note this doesn't support ssh config variables so you need to use the full path.

Forwarding from macOS to Linux:

host gpgtunnel
    hostname remotehost.example.com
    User yourusername
    RemoteForward /home/<user>/.gnupg/S.gpg-agent /Users/<user>/.gnupg/S.gpg-agent.extra

Forwarding from macOS to systemd based Linux, use id -u on the remote system to find your UID:

host gpgtunnel
    hostname systemd-host.example.com
    User yourusername
    RemoteForward /run/user/<remote UID>/gnupg/S.gpg-agent /Users/<user>/.gnupg/S.gpg-agent.extra

Copy the public half of your keys to the remote machine:

scp $HOME/.gnupg/pubring.gpg gpgtunnel:$HOME/.gnupg/

You only have to copy the public half of the private key you are going to use, if you have that handy you can just copy it over and then use gpg --import mypublickey.pub

Now test that the gpg-agent works on the local machine:

echo "test" | gpg --encrypt -r $MYKEYID 
echo "test" | gpg --encrypt -r $MYKEYID > output
gpg --decrypt output

Now ssh to remote machine

scp output gpgtunnel:
ssh gpgtunnel
gpg --decrypt output

The gpg-agent should be able to use your authentication on the local machine.

• https://www.grepular.com/GPG_Agent_Forwarding
• https://wiki.gnupg.org/AgentForwarding