Number of exponentiation operations. This metric gives a measure of the computation load of all members in the communication group.
Number of exponentiation operations this metric pro- vides a measure of the computation load for all mem- bers in the communication group. For simplicity, we assume the following in the analysis: The existing key tree is a completely balanced tree before the interval-based rekeying event. Each member has a homogeneous leave probability. The number of blinded key computations simply equals that of renewed nodes, provided that the blinded key of each renewed node is broadcast only once. For the mathematical analysis, let be the number of members originally in the system, (where ) be the number of members which wish to leave the system, and be the number of new members which wish to join the communication group. Let denote the existing tree which contains members. The level of a node is , where is the node ID, and the maximum level of is . Based on the first assumption, we know that . Also, let be the number of renewed nodes and be the number of exponentiations for the particular algorithm alg. The performance measure is composed of two parts: and , which respectively represent the number of exponentiations of calculating the For the performance measure , we find that when , . If for where , we have (number of members at level ) + (number of members at level )
