ruby net::ssh with keys

$ ssh-keygen -t rsa    
$ ssh-copy-id -i ~/.ssh/id_dsa.pub user@machine
$ ssh user@machine

require 'net/ssh'
require 'logger'

Net::SSH.start(
  'host', 'user',
  :host_key => "ssh-rsa",
  :encryption => "blowfish-cbc",
  :keys => [ "~/.ssh/id_dsa.pub" ],
   :compression => "zlib"
 ) do |session|
   ...
end