# File lib/net/ntlm_http.rb, line 173
      def ntlm_response(arg)
        hash = arg[:ntlm_hash]
        chal = arg[:challenge]
        chal = NTL::pack_int64le(chal) if chal.is_a?(Integer)
        keys = gen_keys hash.ljust(21, "\0")
        apply_des(chal, keys).join
      end