A method of generating a dynamic group key of a group formed of a plurality of nodes, the method including: unicasting a public key that is based on respective secret keys of each of a plurality of general nodes excluding a master node, which is one of the plurality of nodes, wherein the unicasting is performed by the general nodes; broadcasting to the group an encryption value obtained by exponentially-calculating a secret key of the master node to the plurality of public keys, wherein the broadcasting is performed by the master node upon receiving the plurality of public keys; 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, wherein the obtaining is performed by the general nodes.