Ubuntu: encrypted remote desktop server?
It's already installed. Vino. Open the 'Desktop Sharing' dialogue to configure it.
In Ubuntu 14.04 some people seem to have issues with getting Vino to work with encryption, if that is the case you can disable the encryption with: gsettings set org.gnome.Vino require-encryption false
To still achieve encryption this way, you will have to run it through an SSH tunnel.
Here's a list of alternative options: https://help.ubuntu.com/community/VNC/Servers