Patent ID: 7330968

Claim:
A communication network system having a central management device and a plurality of local area network systems, said central management device and said plurality of local area network systems being connected to each other, each of the plurality of local area network systems having a router and a terminal which are connected to each other via a local area network, said central management device comprising: a management database for storing at least one common key, each public key assigned to each router and a public key assigned to the central management device; and a central-side encryption unit for encrypting the common key by using each public key assigned to each router, and sending the encrypted common key to each router; said router comprising: a first router-side decryption unit for decrypting the encrypted common key sent from said central-side encryption unit by using a secret key of the router; a storage unit for storing the common key after decryption by said first router-side decryption unit; a router-side encryption unit for encrypting communication data to be sent from a first source terminal in a local area network system of the router to a first destination terminal in another local area network system, or communication data to be sent from the router to the central management device, by using the common key stored in said storage unit, and sending the encrypted communication data to another local area network or the central management device, wherein said central-side encryption unit encrypts the public keys and sends said encrypted public keys to each router, said first router-side decryption unit decrypts the encrypted public keys sent from the central-side encryption unit by using the secret key of the router, said storage unit stores the public keys after decryption by said first router-side decryption unit, and said router-side encryption unit selects the public key for a router of another local area network system or the central management device to be a destination from the public keys stored in the storage unit, encrypts the common key by using the selected public key, and sends the encrypted common key to another local area network or the central management device, together with the encrypted communication data.