Internet　of　Things　(IoT)　devices　and　systems　are　becoming　increasingly　commonplace,　and　as　such　systems　scale　up,　so　do　the　computational　and　storage　requirements.　Hence,　one　recent　trend　is　to　outsource　data　from　IoT　devices　to　remote　systems.　To　facilitate　both　ciphertext　retrieval　and　data　confidentiality　in　the　outsourced　data,　a　number　of　searchable　encryption　(SE)　approaches　have　been　proposed　in　the　literature.　However,　due　to　limited　keyword　space,　a　number　of　SE　schemes　are　vulnerable　to　keyword　guessing　attacks　(KGAs).　In　addition,　existing　SE　approaches　generally　do　not　consider　the　hierarchical　structure　in　which　users　at　different　levels　require　varying　access　privileges.　Furthermore,　existing　SE　schemes　seldom　provide　time-controlled　access　control.　Therefore,　in　this　article,　we　propose　a　time-controlled　hierarchical　multikeyword　search　by　using　a　double-server　architecture　to　mitigate　KGA.　In　our　approach,　we　also　build　a　public　key　tree　to　support　different　access　permissions　for　hierarchical　users.　Formal　security　analysis　shows　that　our　scheme　is　secure,　and　extensive　experiments　demonstrate　that　our　scheme　is　practical.　©　2014　IEEE.