When asked for a public key authorization an SSH client will, in its default configuration, try all the keys available to it. This means it will expose all the keys you might have to any server that ask. Here is how to fix it if you value your privacy, .
If you have a server that you keep private data on, but it is always on and internet connected, you might want to encrypt that data while you are away. The basic need is to mount data as needed and unmount on timer or log-off.