Hyun Sook Rhee Jong Hwan Park Willy Susilo Dong Hoon Lee Improved searchable public key encryption with designated tester. 376-379 2009 ASIACCS http://doi.acm.org/10.1145/1533057.1533108 conf/ccs/2009asia db/conf/ccs/asiaccs2009.html#RheePSL09