Exporting the public part of your PGP authentication subkey

Enabling gnupg-agent for SSH authentication.sh

# I took this from here: http://www.programmierecke.net/howto/gpg-ssh.html

# Deactivate the gnome-keyring. We will be replacing it with gnupg-agent
gconftool-2 --type bool --set /apps/gnome-keyring/daemon-components/ssh false

# Configure gpg to use the agent
echo "use-agent" >> ~/.gnupg/gpg.conf

# Enable ssh-agent drop in replacement support for gpg-agent
echo "enable-ssh-support" >> ~/.gnupg/gpg-agent.conf

Using gpgkey2ssh.sh

# Find the fingerprint of your authentication subkey.
gpg --list-keys 'your.email@here.com'

# You should see something like:
# pub   4096R/01A35709 2010-01-30 [expires: 2011-06-12]
# uid                  J. Alfred Prufrock <jprufrock@blahblahblah.com>
# sub   2048R/B283E368 2010-01-30   

# That sub is the authentication subkey. Convert it to the SSH format like so:

gpgkey2ssh B283E368 >> ~/my-public-key

# Now use my-public-key as your authorized_keys file on remote servers

# gpgkey2ssh is from the gnupg-agent package yet it has no manpage, no usage, no --help, and is basically undocumented. Awesome, right?

Newer versions of gpg have the --export-ssh-key option.

See this post on the mailing list: https://lists.gnupg.org/pipermail/gnupg-devel/2016-January/030682.html