How are docker certificates used?

I am starting to learn docker machine and have no idea what to do with the keys / certificates that are generated when the docker file is generated:

• id_rsa
• id_rsa.pub
• userdata.tar

How are these keys / certificates used by the docker machine and how do I use them? Can I push these to the repo so others in my project can control the remote docker machine?

Other behavior that confused me:

If I delete the remote machine and create a second machine, the docker machine asks me for the password:

INFO [0000] Create SSH Keypair ...
INFO [Download] Boot ISO Boot2docker ... INFO [Download] /home/username/.docker/machine/cache/boot2docker-1.5.0-GH747.iso to download2docker-iso in the Local Datastore of vCenter 123.456.789.012 ...
INFO [0006] Create virtual machine MyMachineName vCenter 123.456.789.012 ...
INFO Configure virtual machine MyMachineName ...
INFO Power on virtual machine MyMachineName vCenter 123.456.789.012 ...
docker @ 123.456.789.013 password:

But once I remove id_rsa, id_rsa.pub and userdata.tar, the docker machine can create the machine just fine without prompting for a password.

I tried reading the documentation and the only information I found was that keys / certificates can be regenerated using docker's regenerated certificates.

I'm sure I'm just missing some basic, general knowledge and why nothing is documented.

Thank!

This seems to address the same issue, but after reading it, it still wasn't crystal clear:

Controlling remote docker machines from multiple development machines