dropbear is a SSH 2 server and client designed to be small enough to be used in small memory environments, while still being functional and secure enough for general use.
It implements most required features of the SSH 2 protocol, and other features such as X11 and authentication agent forwarding.
1. Install dropbear
apt-get install dropbear
2. Stop OpenSSH server (you won't loose your SSH connection)
2. Enable dropbear (pico /etc/default/dropbear)
3. Start dropbear
4. Remove OpenSSH server
apt-get remove openssh-server