Palash Sarkar Sanjit Chatterjee Construction of a Hybrid HIBE Protocol Secure Against Adaptive Attacks. 51-67 2007 conf/provsec/2007 ProvSec http://dx.doi.org/10.1007/978-3-540-75670-5_4 db/conf/provsec/provsec2007.html#SarkarC07