# File lib/net/ntlm_http.rb, line 161
      def lm_response(arg)
        begin
          hash = arg[:lm_hash]
          chal = arg[:challenge]
        rescue
          raise ArgumentError
        end
        chal = NTL::pack_int64le(chal) if chal.is_a?(Integer)
        keys = gen_keys hash.ljust(21, "\0")
        apply_des(chal, keys).join
      end