SECURITY MAINTAINING METHOD, ITS EXECUTION SYSTEM AND ITS PROCESSING PROCESS

PROBLEM TO BE SOLVED: To provide technique prohibits a tapping person from recognizing a key found by once accident to be really a right key. SOLUTION: A plurality of sets of equipments obtained by connecting a center equipment and a home equipment is set with respect to the single equipment in a network security maintaining method. The method has a step for setting a Mac address of sending destination equipment to the sending destination address of a frame to be transmitted and setting the Mac address of sending source equipment to a sending source address within set of the equipments obtained by connecting the center equipment and the home equipment to cipher the frame with the first ciphering key of the home equipment corresponding to the frame, a step for selecting the frame ciphered by a first ciphering key and ciphering it with the second ciphering key of the home equipment corresponding to the frame, a step for selecting the ciphered frame ciphered by the first ciphering key and deciphering it with the second ciphering key of the corresponding home equipment, and a step for deciphering the frame deciphered by the second ciphering key by the first ciphering key of the corresponding home equipment.