def sign

  def sign(gpg_passphrase="")
      rpm_cmd = "rpm --resign " + self.filename
      rpm_cmd += " 2> /dev/null"

      PTY.spawn(rpm_cmd) do |r,w,pid|
        prompt = r.read(19)

        # match the expected prompt exactly, since that's the only way we know if
        # something went wrong.
        unless prompt == "Enter pass phrase: "
          log_msg = "Unexpected output from `#{rpm_cmd}`: '#{prompt}'"
          log.fatal(log_msg)
          Process.kill(:KILL, pid)
          raise log_msg
        end

        w.write("#{gpg_passphrase}\n")

        # Keep printing output unti the command exits
        loop do
          begin
            line = r.gets
            if line =~ /failed/
              log_msg = "RPM signing failure"
              log.fatal(log_msg)
              raise log_msg
            end
          rescue Errno::EIO
            break
          end
        end
      end
      true
    end