I recently replaced my old Yubikey with one of the new Yubikey NEO’s, I wanted a simple and secure way of storing my GPG key as well 2 factor authentication.
This post is about setting up and fixing Ubuntu 14.04 and 14.10 to enable ssh-agent functionality in gpg-agent. I assume that you have already securely generated and stored a gpg key in the Yubikey and have imported the key stubs into gpg.
This post is rather complex because Seahorse the gnome-keyring manager “supports” ssh and gpg agent type functionality and takes over ssh-agent and gpg-agent. The problem with Seahorse is that it doesn’t work with OpenPGP cards and a secondary problem is that you need to disable a number of other ssh key services.
First you will need to install the following packages, gnupg-agent and pcscd the smart card management service.
sudo apt-get install gnupg-agent pcscd
You need to disable gnome-keyring’s ssh and gpg agent functionality, bug id 1387303 contains a fix allow this which has now been released as gnome-keyring – 3.10.1-1ubuntu7.1. Once this is installed you can disable the ssh and gpg agents in Unity’s startup applications found under the settings menu.
You will need to enable both gpg-agent support in gpg and then ssh-agent support in gpg-agent. In the $HOME/.gnupg directory add the line use-agent to gpg.conf and enable-ssh-support gpg-agent.conf you may need to create the files.
Next you need to install a fixed version of the gnupg-agent upstart init script so that it starts gpg-agent correctly with ssh key support. Install this script into the .init directory in your home directory this overrides the system wide one.
mkdir $HOME/.init wget -O $HOME/.init/gnupg-agent.conf http://www.programmierecke.net/howto/gpg-agent.conf
Finally you need to disable the “real” ssh-agent by commenting out the line in /etc/X11/Xsession.options, there aren’t any override options that I know of.
After restarting X or a reboot you should find that ssh-agent -L prints out a long ssh key string, you are looking for the one that ends in card:XXXXX this is the public half of your Yubikey gpg key in ssh key format.
With gnupg-agent providing ssh-agent services, you can use ssh-add to import existing SSH private keys into gpg’s key secure storage.
Hints and methods taken from: http://www.programmierecke.net/howto/gpg-ssh.html