Agnes Hui Chan Rajmohan Rajaraman Zhifeng Sun Feng Zhu Approximation Algorithms for Key Management in Secure Multicast. 148-157 2009 COCOON http://dx.doi.org/10.1007/978-3-642-02882-3_16 conf/cocoon/2009 db/conf/cocoon/cocoon2009.html#ChanRSZ09