Dario Freni Sergio Mascetti Claudio Bettini Hide & Crypt: Protecting Privacy in Proximity-Based Services. 441-444 2009 SSTD http://dx.doi.org/10.1007/978-3-642-02982-0_36 conf/ssd/2009 db/conf/ssd/sstd2009.html#FreniMB09