Allow admin to restrict min SSH key length and technology

Intro

The default key length produced by programs like ssh-keygen in linux, are starting to become too short for real security.

Problem

The admin does not have control over the key length or type for the ssh keys. This is something that could become a problem as the brute force cracking of keys becomes less difficult.

Proposal

Add the ability for the admin to set a minimum key length, and, if relevant, restrict broken encryption technologies.

~"feature proposal"