sshd - public key vs keyboard interactive authentication

[Danie Du Toit]

5.3 with OpenSSH.

Using public key authentication:

I generated/converted my keys - all set, I can ssh to the box using
the keys (no user authentication, I get logged in)

Using password authentication:

I can still ssh using interactive keyboard password authentication
(without using public/private keys).

So, my questions:

1. How do I disable password authentication - i.e. force to use the DSA keys?

2. Can I use both for added security - i.e.  using the keys and then
get prompted for password?

Any help appreciated - thanks