This option allows for SSH access to be granted to the domain owner user using public key authentication. The options are:

No default key
  Don't setup an SSH key. Only logins with a password will be allowed.

Generate public and private keys
  Create a new SSH key pair for this virtual server, and allow logins using that key. The server owner should copy the private key after creation.

Use public key below
  SSH logins will be allowed using the private key that corresponds to the public key entered in the text box below.