Artak Amirbekyan Vladimir Estivill-Castro The Privacy of k-NN Retrieval for Horizontal Partitioned Data -- New Methods and Applications. 33-42 2007 ADC http://crpit.com/abstracts/CRPITV63Amirbekyan.html conf/adc/2007 db/conf/adc/adc2007.html#AmirbekyanE07