Patent ID: 8553887

Claim:
A method of generating a dynamic group key of a group formed of a plurality of general nodes and a master node, said method comprising: each of the general nodes generating a public key that is based on respective secret keys of the general nodes and unicasting the public key of each of the general nodes to the master node; the master node generating an encryption value obtained by exponentially calculating a secret key of the master node to the plurality of each of the public keys, and broadcasting a message including the encryption values to each of the general nodes; and (each of the general nodes obtaining the encryption value of each of the general nodes from the message, and obtaining a group key by using an inverse power calculation of the respective secret keys of each of the general nodes based on the encryption value of each of the general nodes; leaving the group, wherein the leaving is performed by at least one general node from among the plurality of nodes; broadcasting to the group an encryption value obtained by exponentially calculating a new secret key of the master node to the remaining public key excluding the public key of the at least one general node that left the group, wherein the broadcasting is performed by the master node; and obtaining a new group key by using an inverse power-calculation of respective secret keys of each of the remaining general nodes in the group based on the encryption value, wherein the obtaining is performed by the all remaining general nodes in the group.