Method and apparatus for updating a group key

A computer-readable storage medium storing a program for implementing a method of updating a group key of a group which corresponds to a binary tree, comprising:

• a first set of instructions for updating keys of leaf nodes corresponding to new members in response to a join of at least two new members joining the group;
• a second set of instructions for determining whether both of two child nodes of a single ancestor node are updated when updating a key of the ancestor node of the leaf nodes;
• a third set of instruction for establishing one of the two child nodes as an update use node when both the two child nodes are updated;
• and
• a third set of instructions for updating a key of the ancestor node using the updating node.

An apparatus for updating a group key of a group corresponding to a binary tree, the apparatus comprising:

• an update determination unit for determining whether two child nodes of a single ancestor node are both updated when updating a key of the ancestor node of the leaf nodes, in response to at least two new members joining the group;
• an update use node determination unit for determining one of the two child nodes as the update use node when the two child nodes are both updated;
• and
• a key update unit for updating the key of the ancestor node using the update use node.