Generate the keys using the command ssh-keygen -t dsa and follow the prompts. If you're going to use the shared key to log into a system where user identities shouldn't be shared (i.e iVEC) save the key file as something like /home/observer/.ssh/id_dsa_username_galaxy, and use a non-blank passphrase

scp the file to the target computer (which you want to be able to access using the shared key) with scp .ssh/id_dsa_username_galaxy username@galaxy.org:

ssh into the target system (using your usual password) and include the shared key in the .ssh/authorized_keys file with a command like cat id_dsa_username_galaxy » .ssh/authorized_keys

You can now use the shared key to log in to the target system. If you want to avoid having to enter a password/phrase repeatedly, use ssh-agent bash and ssh-add .ssh/id_dsa_username_galaxy. You'll have to enter your passphrase once this way.