Patent ID: 8509443

Claim:
A rekey index generation method, the method comprising: inserting join information into a first field of a rekey index when new members join a group; splitting one or more existing nodes corresponding to one or more existing members to generate new nodes corresponding to the new members and the one or more existing members; inserting new node numbers, corresponding to each of the new members, into a second field of the rekey index in an order that enables a receiver to select a necessary key from among transmitted encoded keys based on the order of the new node numbers included in the second field; and transmitting, to one or more receivers corresponding to one or more update target nodes, encoded keys for each respective update target node and the rekey index comprising leave information in the first field, the node numbers of the highest nodes of ancestor nodes in the group whose descendant leaf nodes all leave in the second field, and the node numbers of all nodes connected with only one member in the third field.