Group cipher communication method and group cipher communication system

摘要

Method and system which permit, among a plurality of terminals, group cipher communication from a desired terminal to a number of desired terminals while ensuring safety of security. A plurality of secret values called master keys which are common to a predetermined subset of IC cards are stored in an IC card. A terminal initially starting communication generates a destination indicator to transmit it to other terminals, selects one of a plurality of master keys stored in an IC card on the basis of the destination indicator, generates a group key by using the selected master key, and performs encipherment and decipherment of a communication message by using the generated group key to carry out broadcast. A terminal standing for a destination receives the destination indicator, selects one of a plurality of master keys on the basis of the destination indicator, generates the group key on the basis of the selected master key and performs encipherment and decipherment of the communication message by using the generated group key.