COMMUNICATION SYSTEM AND SECURITY ASSOCIATION DISCONNECTION/CONTINUING METHOD

摘要

PROBLEM TO BE SOLVED: To provide a communication system, capable of preventing communication disconnection from being generated due to old security association. SOLUTION: In this communication system, a ciphering device 6 changes the identifier (IP address) for identifying own device, and transmits security isolation disconnection notification (ISAKMP disconnection notification) including a 'pre-changed identifier' and 'security isolation release (ISAKMP release)', enciphered by using a key for encipherment and a key for authentication to a ciphering device 5 which is the communicating party. Then, the ciphering device 5 decodes the security isolation disconnection notification, by using the key for encipherment and the key for authentication, executes mutual authentication, and disconnects the old security association.