1. A method for generating a group key applied to a plurality of nodes, comprising: sharing a first secrete key with a first adjacent node of a plurality of nodes adjacent to a first node of the plurality of nodes and a second secrete key with a second adjacent node of the plurality of adjacent nodes; obtaining first and second function values by using the first and second secrete keys and obtaining an inner result value by using the first and second function values; broadcasting the inner result value; receiving a plurality of inner result values from nodes of the plurality of nodes except for a corresponding node of the plurality of nodes; and performing an operation on a plurality of function values extracted from the first function value and the plurality of outer result values to obtain a group key.