Multi-keyword　rank　searchable　encryption　(MRSE)　returns　the　top-k　results　in　response　to　a　data　user＇s　request　of　multi-keyword　search　over　encrypted　data,　and　hence　provides　an　efficient　way　for　preserving　data　privacy　in　cloud　storage　systems　while　without　loss　of　data　usability.　Many　existing　MRSE　systems　are　constructed　based　on　an　algorithm　which　we　term　as　k-nearest　neighbor　for　searchable　encryption　(KNN-SE).　Unfortunately,　KNN-SE　has　a　number　of　shortcomings,　which　limit　its　practical　applications.　In　this　paper,　we　propose　a　new　MRSE　system　which　overcomes　almost　all　the　defects　of　the　KNN-SE　based　MRSE　systems.　Specifically,　our　new　system　does　not　require　a　predefined　keyword　set　and　supports　keywords　in　arbitrary　languages,　is　a　multi-user　system　which　supports　flexible　search　authorization　and　time-controlled　revocation,　and　it　achieves　better　data　privacy　protection　since　even　the　cloud　server　is　not　able　to　tell　which　documents　are　the　top-k　results　returned　to　a　data　user.　We　also　conduct　extensive　experiments　to　demonstrate　the　efficiency　of　the　new　system.　©　2004-2012　IEEE.