As　cloud　storage　has　been　widely　adopted　in　various　applications,　how　to　protect　data　privacy　while　allowing　efficient　data　search　and　retrieval　in　a　distributed　environment　remains　a　challenging　research　problem.　Existing　searchable　encryption　schemes　are　still　inadequate　on　desired　functionality　and　security/privacy　perspectives.　Specifically,　supporting　multi-keyword　search　under　the　multi-user　setting,　hiding　search　pattern　and　access　pattern,　and　resisting　keyword　guessing　attacks　(KGA)　are　the　most　challenging　tasks.　In　this　article,　we　present　a　new　searchable　encryption　scheme　that　addresses　the　above　problems　simultaneously,　which　makes　it　practical　to　be　adopted　in　distributed　systems.　It　not　only　enables　multi-keyword　search　over　encrypted　data　under　a　multi-writer/multi-reader　setting　but　also　guarantees　the　data　and　search　pattern　privacy.　To　prevent　KGA,　our　scheme　adopts　a　multi-server　architecture,　which　accelerates　search　response,　shares　the　workload,　and　lowers　the　key　leakage　risk　by　allowing　only　authorized　servers　to　jointly　test　whether　a　search　token　matches　a　stored　ciphertext.　A　novel　subset　decision　mechanism　is　also　designed　as　the　core　technique　underlying　our　scheme　and　can　be　further　used　in　applications　other　than　keyword　search.　Finally,　we　prove　the　security　and　evaluate　the　computational　and　communication　efficiency　of　our　scheme　to　demonstrate　its　practicality.　©　1990-2012　IEEE.