gistfile1.rb

require 'tempfile'

def check_authorized_keys(keyfile)
  @found_ssh = false
  File.foreach(keyfile) do |line|
    if line =~ /^ssh/
      @found_ssh = true
      Tempfile.open('key') do |keyfile|
        keyfile.write(line)
        keyfile.flush
        result = %x[echo #{keyfile.path} | ssh-keygen -l 2>&1]
        if result =~ /not a public key/
          keyfile.unlink
          return false
          break
        end  
        keyfile.unlink
      end
    end
  end
  return @found_ssh
end

p "CHECKING BAD"
p check_authorized_keys('/tmp/testkeyfile')
p "CHECKING GOOD"
p check_authorized_keys('/home/stephen/.ssh/authorized_keys')