Takao Takenouchi Takahiro Kawamura Akihiko Ohsuga Distributed Data Federation without Disclosure of User Existence. 282-297 2012 DBSec https://doi.org/10.1007/978-3-642-31540-4_22 conf/dbsec/2012 db/conf/dbsec/dbsec2012.html#TakenouchiKO12