Kilho Shin Hiroshi Yasuda Provably Secure Anonymous Access Control for Heterogeneous Trusts. 24-33 2006 conf/IEEEares/2006 ARES http://doi.ieeecomputersociety.org/10.1109/ARES.2006.98 db/conf/IEEEares/ares2006.html#ShinY06