Balanced and Imbalanced GKA schemes. Balanced and Imbalanced is another classification method of GKA schemes except for the PKI-based, ID-based and certificateless-based schemes introduced above. The concept of balanced and imbalanced is come from the wireless network domain. One way to categorize different kinds of wireless networks is to classify them into balanced and imbalanced wireless network. In the balanced network, all nodes have the same level of computing power. In imbalanced wireless network, there are two classes of nodes: low power node(like smartphone in mobile network) and powerful node(like servers in mobile network), where powerful nodes have a much higher computation level. In the group key management domain, the concept of “imbalanced” is similar to the group key distribution schemes: One high-level key management server calculates the group key and distributes it to all group members. The concept of “balanced” is similar to the group key agreement schemes: all group members make the same contribution to the group key. Based on the similarity of the concept between balanced wireless network and group key agreement scheme, it seems that all group key agreements schemes should be balanced schemes. However, there could be a hybridization of group key distribution scheme and group key agreement scheme. In this hybridization scheme, all group members make contributions to the group key, but one of them might make more contribution or perform major parts of computation. This kind of hybridization scheme cannot be classified into key distribution scheme since the group key is not only generated by one powerful node, but it can be classified into key agreement scheme since the group key is generated by all members. Therefore, the concept of balanced and imbalanced can be used in the group key agreement domain. The group key agreement schemes can be classified into balanced and imbalanced GKA scheme, and the concept of imbalanced GKA scheme is the same as the hybridization scheme mentioned above. The GKA scheme from Nam et al. in 2005 [84] first shows the idea of imbalanced GKA scheme, because it considers the environment of mobile network, which is definitely a kind of imbalanced wireless network. However, Xxxxx criticized that Xxx’s scheme lacks contributory property because the group members cannot confirm their contribution to the group key in his scheme, then Xxxxx proposed his own scheme[85]. Unfortunately, Xxx et al. pointed out that Xxxxx’x scheme lacks authentication and c...
