Mikhail J. Atallah Marina Blanton Nelly Fazio Keith B. Frikken Dynamic and Efficient Key Management for Access Hierarchies. 2009 12 ACM Trans. Inf. Syst. Secur. 3 http://doi.acm.org/10.1145/1455526.1455531 db/journals/tissec/tissec12.html#AtallahBFF09