Zhi-Zhong Chen Ze Feng Minming Li F. Frances Yao Optimizing deletion cost for secure multicast key management. 52-61 2008 401 Theor. Comput. Sci. 1-3 http://dx.doi.org/10.1016/j.tcs.2008.03.016 db/journals/tcs/tcs401.html#ChenFLY08